Int. J. Prenatal and Perinatal Psychology and Medicine Vol. 21 (2009) No. 1/2, pp. 4–16
Time Table of Normal Foetal Brain Development
Otwin Linderkamp, Ludwig Janus, Rupert Linder, and Dagmar Beate Skoruppa
Abstract: The foetal brain develops within few weeks from a thin cell layer to a gigantic
and complex network with billions of neurons and trillions of connections. This process
is influenced by environmental factors (e.g. maternal stress) from the beginning. Under-
standing of the developmental processes is the basis of prenatal medicine and psychology.
Five steps can be related to fairly defined time periods: (1) From 7 to 22 weeks of gestation
20 billion neurons are produced and migrate to their final locations in the brain. (2) From
20 to 35 weeks the transient subplate structure lays the foundation of the cortex. (3) The
organization of the neural network (nerve fibre and synapse formation) starts at 24 weeks
gestation and continues throughout life. (4) Individual adjustment of the neural network
by elimination of more than 50% of the neurons and circuits also starts at 24 weeks, and
shapes the brain in three waves. (5) Myelination of axons begins during the last weeks of
gestation and continues for decades.
Keywords: cortex, gestational age, neuron, prenatal, subplate, synapse
Introduction
During the last twenty years, foetal brain development has become an essen-
tial topic of neuroscience as a result of modern non-invasive and computational
techniques and animal models. The results allow quantitative description of the
structure and development of individual nerve cells and entire networks within
specific brain areas, and to relate the structures to the functions at both the sin-
gle neuron and network levels (Berzhanskaya and Ascoli 2008). Recent results
support the hypotheses of publications on prenatal psychology emphasizing the
importance of environment and experience for the normal psychological devel-
opment of the foetus (Fedor-Freybergh and Vogel 1988; Janus 2001, 2007; Janus
and Linder 2006; Ridgeway and House 2006).
Several reviews on foetal brain development appeared during the last years
(De Graaf-Peters and Hadders-Algra 2006; Eliot 2000; Gilbert 2001; H¨uther and
Krens 2006; Lagercrantz et al. 2002; Linderkamp 2005; Ridley 2003; Rutter 2006;
Turkewitz 2007). Our present review is designed to summarize the present knowl-
edge of foetal brain development with emphasis on the time-table of the events
shaping the brain. Our paper provides the basis of understanding experience-
dependent brain development and effects of maternal anxiety and stress on the
brain and long-term outcome. Subsequent papers of our group will focus on these
topics (Linderkamp et al. 2010a, b).
Time Table of Normal Foetal Brain Development 5
Early Human Brain Development
The brain development begins at approximately three weeks after conception
(5 weeks of gestation) with the formation of the neural plate at the back of the
embryo. A few days later the plate folds to form the neural tube around a canal.
In the brain the canal later widens to the ventricles, in the spinal cord it forms the
central canal. At the time of neural tube closure the neural wall consists of one
or two layers of epithelial cells (neuroepithelium) which are the precursors of an
enormous variety of neurons and the macroglia.
The development of the cerebral cortex occurs in precisely-timed stages
(Table 1, Fig. 1). Each developmental process is also a vulnerable period which
is sensitive to environmental insults rendering the brain susceptible to structural
malformations and functional impairments.
10 15 20 25 30 35 40 6 12 24 4 8 16 32
Neurulation
Neural proliferation
Neuronal migration
Subplate neurons
Axon growth
Synapse formation
Glia proliferation
Myelination
Neuronal death
Fibre retraction
Synapse elimination
10 15 20 25 30 35 40 6 12 24 4 8 16 32
months years
Postnatal Age
weeks
Gestational Age
Fig. 1. Time table of developmental events of the human brain during foetal and postnatal
life. Black shaded areas indicate peak activities, open lined areas indicate low or medium
activity.
Neurogenesis: “Raw Material” for the Brain
Billions of nerve cells (neurons) are produced during the development of the cen-
tral nervous system. Neurogenesis mainly occurs at the inner edge of the neural
tube wall, the later ventricles (brain) and central canal (spinal cord), respectively
(Fig. 2). In preterm infants the reproduction zone is still visible on ultrasound
scans (“subependymal germinal matrix”). Cell division begins once the neural
6 Otwin Linderkamp et al.
Table 1. Major events in foetal cortical development.
Peak occurrence* Major developmental events Abnormal development
5-9 wk Primary neurulation (neural tube
formation)
Prosencephalon formation
(precursor of haemispheres)
Anencephaly
Encephalocele**
Meningomyelocele
Spina bifida**
12-18 wk
(6 wk to life long)
Neuronal proliferation (neurogenesis) Encephalocele, microbrain**
Schizophrenia**
12-20 wk
(8-30 wk)
Neuronal migration
Formation of cortical cell layers
Heterotopias (wrong place);
reduced or no gyration:
reduced attention and cognition,
depressive signs**
22-34 wk
(15-38 wk)
Subplate neurons (guidance of axons
between thalamus, cortex and
subcortical structures;
final migration of neurons)
Impaired development of thalamus
and cortex and connecting circuits:
disorders of frontal, temporal and parietal
centers**
24 wk to 15 mo
(10 wk to life-long)
Outgrowth of axons
Outgrowth of dendrites
Synaptogenesis
White matter reduction
Cortical dysplasias:
Down, fragile-X syndrome sensory,
behavioural, cognitive disorders**
24-38 wk
(20-44 wk)
24 wk to life-long
Selective death of neurons
Elimination of synapses
Excessive loss of neurons and connecting
circuits: cognitive, sensory, behavioural,
psychiatric disorders**
15 wk to 18 mo
(6 wk to life-long)
Glial cells proliferate und differentiate
(structural support, neuronal migration,
myelin, “clean up”)
Impaired neuronal migration
Loss of dendrites and synapses in frontal
cortex, hippocampus, amygdale
35 wk to 24 mo
(15 wk to adulthood)
Myelination Dysfunction of axons: psychiatric,
cognitive disorders**
Abbreviatons: IQ, intelligence quotient; p.n., mo, months postnatal; wk, weeks gestation
*Gestational (postmenstrual) age; in parentheses, occurrence prolonged at slower pace.
**Increased risk due to maternal stress has been shown in human foetuses or animal models (from Linderkamp et al. 2010b).
tube has closed at 4 to 5 weeks after conception (6 to 7 weeks of gestation). The
majority of neurons are formed at 12 to 18 weeks of gestation. Approximately
100 000 neurons are produced during each second to provide a number of at least
200 billion (2 × 1011) neurons in the human brain and 40 billion in the neocortex
alone. Approximately 50% of the neurons are eliminated during the later mat-
uration process, resulting in a final number of 100 billion neurons at 40 weeks
(full-term).
Proliferation of neurons during the first 22 weeks of gestation is mainly deter-
mined by genetic factors (Bourgois 2002). However, severe maternal stress during
the first trimester (i.e. neurulation and early neurogenesis) has been linked to an
increased risk of encephalocele (Hansen et al. 2000) and schizophrenia (Khashan
et al. 2008), suggesting that the expression of genes in early foetal life is influ-
enced by external factors. Stress-induced reduction of neurons in late foetal life
is probably the result of increased damage of neurons (Fabricius et al. 2008).
Time Table of Normal Foetal Brain Development 7
Fig. 2. Section through the cortex at approximately 24 weeks of gestation. Note that the
germinal zone adjoins to the ventricle at the inner edge of the cortex. Newly formed neu-
rons migrate along the radial glia through the subplate and previously formed neuronal
layers to the upper layer of the cortical plate.
If the brain is sufficiently used and trained, new neurons are generated through-
out life. Neural stem cells and pluripotent radial glia cells are able to differentiate
into neurons in the adult brain (Mo et al. 2007). In mice, neurogenesis increased
the efficiency of learning, but did not affect long-term memory (Zhang et al.
2008). The formation of new synapses and the prevention of neuronal damage
are far more important mechanisms for life-long learning than the formation of
new neurons (Uylings et al. 2005).
Migration of Neurons: Finding the Right Place
After several divisions neuroblasts lose their ability to divide and they begin to
move away from the inner multiplication zone to the outer edges of the growing
neural tube wall. Once a neuron has reached its final destination within the correct
cortical layer, it will stay there for life. The first neurons start migration with the
beginning of multiplication, the majority of cells move to their layer between 12
and 20 weeks of gestation (Gressens 2005).
Both passive pushing by subsequently migrating neurons and active movement
of neurons are mechanisms of migration. In the cortex, neurons move radially
outwards to the surface along specialized radial glial fibres (Fig. 2), which span
the entire thickness of the hemisphere from the ventricular surface to the external
pial surface (Rakic 2003). This “ladder” facilitates the journey through the earlier
arriving cell layers. At the brain surface, the neurons leave the ladder and move
8 Otwin Linderkamp et al.
Table 2. Maturation of nerve cells in the cortex.
Step Events
Neurogenesis Subventricular stem cells divide symmetrically. The last division results in
larger neurons before they migrate.
Radial glia Generated from same stem cells a neurons.
Form long processes through the entire cortex (fig. 2).
Migration Neurons climb on radial glia to cortical surface.
Contact to subplate
neurons
Migration through subplate neurons (fig. 2) and contact to thalamo-cortical
and cortico-cortical fibres may accelerate their maturation.
Formation of six
cortical layers
Neurons migrate through previously formed layers to the surface. Thus, the
early-migrating cells form the superficial layer, the latest the deepest until six
cortical layers have been established. Neurons assemble in columns above
the stem cells and are therefore clonally related.
Astrocyte formation Astrocytes are generated from radial glia.
Life-long neurogenesis New neurons are generated from remaining subventricular stem cells and
locally from radial glia.
laterally to give way to the subsequently arriving neurons and to form a layer at
the surface of the cortex. Then the next group of migrating cells passes through
this layer and forms a new layer at the surface. This process continues until six
layers have been formed. Thus, the earlier generated neurons form the deepest
cortical layer, and the latest cells settle in the most superficial layer (inside-out
order). The radial migration of neurons originating from the same reproduction
site results in columns of clonally related cells. This may be important for their
specialized functions in their final cortical destination.
Insufficient movement or migrations to wrong places result in heterotopias
which may be associated with serious malformations as lissencephaly (reduced
gyration, “flat brain”), epilepsy and mental retardation (Gressens 2005; Nicolic
and Reynolds 2008). Although normal migration of neurons to the right location
is probably determined by genes (Rutter 2006), abnormal migration is mostly the
result of environmental factors. Maternal stress during the gestational age of max-
imal neuronal migration has been shown to predispose the offspring to a variety of
impairments including reduced attention span, cognitive problems and depressive
symptoms (van den Bergh et al. 2008).
Organisation of the Neural Network
The first two steps, multiplication and migration of primitive nerve cells, are mostly
completed at 22 weeks of gestation. At the beginning of migration neurons are
not yet specialized, but they lose their pluripotency once they have reached their
final position in a specialized region of the central nervous system.
Organization of an individual neuron refers to the establishment of connec-
tions with other cells and the specialization to distinct functions within the neural
network. Organization of the total central nervous system refers to the formation
of the entire neuronal network and its capacity to operate as an integrated whole.
Time Table of Normal Foetal Brain Development 9
Table 3. Major steps of neural organisation of the cortex (modified from Volpe 2008).
Goal:
Establishment of a functioning neural network
Major period:
20 weeks of gestation to years after birth
Steps:
• Formation of subplate neurons with initial fibre and synapse formation.
• Formation of the cortical plate with six layers of aligned neurons.
• Outgrowth of nerve fibres (axons, dendrites) and their ramifications.
• Synptogenesis.
• Selective elimination of neurons (apoptosis), nerve fibres and synapses.
• Proliferation and differentiation of neuroglia.
The process of organization starts at approximately 22 weeks of gestation and
includes actions of subplate neurons, outgrowth of neural fibres, synaptogenesis
and myelination.
Subplate Neurons: Pioneers Paving the Wire Tracks
Subplate neurons play a major role in the development of the gigantic network
connecting billions of neurons and are probably responsible for the evolution of
the neocortex. The subplate zone is situated between the intermediate zone (pre-
cursor of white matter) and the cortical plate with the six layers of neurons (Fig. 2).
In magnetic resonance images, the subplate is visible as a continuous band in the
entire cortex at 20–27 weeks of gestation, starts to disappear in the parietal lobe
at 28 weeks, but remains prominent in the frontal lobe up to 35 weeks (Perkins et
al. 2008). At 38 weeks, 90% of the subplate neurons have disappeared.
The subplate neurons excrete neurotransmitters that attract axons ascending
from the thalamus and dendrites descending from cortical neurons for transient
connections with the subplate neurons. When the subplate neurons die, the tha-
lamic and cortical neurons become directly connected (thalamo-cortical tracts).
Moreover, subplate neurons help cortical neurons to establish connections with
other cortical neurons in both hemispheres and to guide the final migration of
cortical neurons within the six layers. They help to balance excitation and inhi-
bition in cortical layers, which is important for the “plasticity” of brain functions
(Kanold and Shatz 2006). The transient connections among various brain cen-
tres via subplate neurons are the basis for early foetal (and preterm’s) behaviour
(Kostovics and Jovanov-Milosevic 2006).
Maternal stress during the peak actions of subplate neurons from 22 to 34
weeks gestation has been linked to developmental delays, lower IQ, behavioural
problems and schizophrenia in offsprings (Bergman et al. 2007). It is likely that
the stress exposure of preterm infants during intensive care can alter subplate
neurons, thereby contributing to the high risk of preterm infants to long-term
cognitive and behavioural problems.
10 Otwin Linderkamp et al.
Wiring the Neural Network: Axons, Dendrites and Synapses
The set-up of a functioning neural network connecting all parts of the central
nervous system and other target organs requires trillions of connections among
neurons via axons, dendrites and synapses. The migrating cells have no function-
ing axons and dendrites. Having migrated to the appropriate position, axons and
dendrites begin to grow out of the young neurons.
Usually one axon only arises from each cell (Fig. 3). Axons are the long nerve
fibres connecting distant parts within the central nervous system and with pe-
ripheral organs (e.g. muscles and glands). Their final length can be more than
a meter in adults, but also just a few µm, if they connect adjacent neurons. Ax-
ons develop many branches at the tip and each final branch can form a synapse
with a final branch of a dendrite or sometimes another axon or a nerve cell body.
Dendrites emerge from many points along the cell body and appear very much
like branches on a tree. Axons and dendrites find their target cells principally
by growing in the direction of the targets. This growth is guided by molecules
bound to cells (for short-range chemoattraction) or diffused in the environment
(long-range chemoattraction, e.g. nerve growth factor). Target cells also present
and secrete chemorepellents that inhibit the growth of connecting nerve fibres
to these cells. The search of outgrowing fibres for target neurons can be highly
specific or more or less arbitrary. Specific connections are formed between neu-
rons that express specific marker molecules, thereby giving the connecting cells
no choice (cell specificity). Other neurons are attracted to send fibres to neurons
in a defined region (topographic specificity).
Synapses are formed by proteins acting as molecular switches between two
nerve fibres. Chemoattractants determine when and where synapses are formed
and their specificity and stability. Moreover, formation, specificity and stability of a
synapse depend on the quality and quantity of impulses travelling through the con-
necting fibres. Synaptic activity provides critical information about the usefulness
of synaptic connections, thereby influencing synapse stability and maintenance
(Waites et al. 2005). Synaptic activity promotes the formation of new synapses
and strengthens existing synapses in the neighbourhood. Thus, synapse formation
and stabilization are dynamic processes, requiring bi-directional communication
between connected partners. Subtle alterations in synaptic connections are the
means by which learning wires the pathways to memory (Ge et al. 2007).
Although the first synapses are produced already at 8 weeks of gestation,
synapse formation is slow until 24 weeks of gestation resulting in a total num-
ber of synapses that is not much higher than the total number of neurons. From
24 weeks gestation to 12 months of postnatal age, a myriad of connections is
formed among billions of neurons. At full-term each cortical neuron is linked
with approximately 2500 other neurons, at 12 months of postnatal age with 15 000
(Petanjek et al. 2008). Synaptogenesis begins in a relatively short time period in all
cortical regions, but the maximum synaptic density is reached at different times
after full-term, ranging from 3 months in the auditory and visual cortex to 15
months in the prefrontal cortex (Bourgeois 2002).
After the first year of postnatal life the total synapse number slowly increases
and reaches the maximum at five years when the child’s brain weighs almost as
much as in adults. Then the number of synapses plateaus until about 10 years and
Time Table of Normal Foetal Brain Development 11
Fig. 3. Neurons with one axon and several dendrites arising from the neuronal cell body.
The left neuron represents the development in the sensory cortex at approximately 24–
28 weeks, the right neuron at 32–40 weeks. Note the marked differences in ramifications
between the two neurons.
begins to decrease by approximately 40% with the onset of puberty. Thus, dur-
ing the first 5–10 years of life, the child achieves the highest number of synapses,
thereby enabling the child to acquire enormous behavioural, social, environmen-
tal, linguistic and cultural information. After the age of five years, synaptogenesis
continues as a local event (Bourgeois 2002) in dependence on the activity of
neighbouring synapses. Formation of new synapses and changes of specificity and
stability of synapses are fundamental to life-long learning, memory and cognition
in the mature brain (Waites et al. 2005).
Outgrowth of fibres and formation of synapses are largely influenced by envi-
ronmental factors, including sensory experience. Both decreased sensory input of
the foetus and maternal stress may cause a marked reduction of axons, dendrites
and synapses in the prefrontal cortex, the hippocampus and other brain centres
(Linderkamp et al. 2010b).
Glial Cells and Myelination
Glial cells (also called neuroglia) are non-neuronal cells that outnumber neu-
rons by about 10 to 1, but constitute only half of the brain volume, since they are
smaller than neurons. Glial cells surround neurons and hold them in place, play
an important role in neuronal and axonal guidance, supply nutrients and oxygen
to neurons, produce and remove chemical transmitters, insulate axons by myelin,
12 Otwin Linderkamp et al.
destroy pathogens, dead neurons and other debris, and contribute to formation
of new neurons. Glial cells are crucial in the development of the nervous system
and in processes such as synaptic plasticity and synaptogenesis. Various types of
glial cells are defined by origin, appearance and functions (Table 4).
Macroglial cells comprise radial glia, astrocytes and oligodendrocytes and de-
velop from the same stem cells in the ventricular zone of the neural tube as the
neurons. Radial glia cells are the progenitors of astrocytes, some oligodendro-
cytes and neurons. In the developing brain, radial glia functions as a “ladder”
upon which neurons migrate to the surface of the cortex. Microglia are special-
ized immune cells capable of phagocytosis. They are derived from haemopoietic
precursors as other immune cells.
Oligodendrocytes produce myelin that forms insulating sheaths around axons.
Schwann cells provide myelination to axons in the peripheral nervous system.
Myelin is a white fatty material wrapped around most neural axons. It prevents
the leakage of ions and thus of electrical current from the axon, thereby increasing
the speed of nerve conduction by ten to one hundred times. Moreover, myelin pre-
vents erratic activation of adjacent axons. Without myelin, electric activity would
be aimlessly distributed throughout the brain, and information would become
chaotic. Myelination also inhibits plasticity, since a myelinated axon has less abil-
ity to branch out and connect with other neurons. Myelin is involved in cognitive
functions and learning (Fields 2008).
Myelination starts in the spinal cord (at about 12 weeks gestation), then in
brain stem (14 weeks) and thalamic axons (20 weeks), and finally in the cortex
(35 weeks) and continues for decades in the human brain (Miller et al. 2003).
Axons connecting the frontal-limbic system (responsible for complex cognitive
functions) start to myelinate after birth. Late myelination explains that the brains
of infants and young children are slow compared with adult brains. Myelination
is modifiable by experience and severe maternal or postnatal stress may inhibit
myelination, thereby contributing to psychiatric disorders, including schizophre-
nia and depression, and cognitive impairment (Fields 2008).
Shaping the Brain by Elimination of Excess Neurons and Circuits
At least twice as many neurons as necessary are produced during the time period
of active neuronal multiplication, and most of the excess neurons are eliminated
during maturation of the neuronal network (“programmed cell death” or apop-
tosis). Three peak periods of neuronal death can be distinguished (Fig. 1): 1) at
the beginning of neurogenesis; 2) from 24 to 38 weeks gestation; and 3) between
the onset of puberty and adulthood (Lossi and Merighi 2003).
The second and third periods are linked to selective elimination of axons, den-
drites and synapses. Production of neurons and growth of axons and dendrites in
the direction of target cells are not very selective and result in overproduction of
connections. The initial wiring is diffuse, with a lot of overlap making commu-
nication inaccurate and disorganized. Elimination of fibres, synapses and entire
neurons allows quantitative adjustments of connections between neurons and to
compensate for errors of cell migration (mislocation) and projection of axons and
dendrites (misprojection). Elimination of neurons, fibres and synapses parallels
Time Table of Normal Foetal Brain Development 13
Table 4. Glial cells.
Cell type
Structure
Functions
Radial glia
Long radial processes spanning the
thickness of the cortical wall
Progenitors of neurons and astrocytes
Guidance of neurons and nerve fibers
Regulation of synaptic plasticity
Astrocytes
Support cells with short, thick processes
for neurons (“protoplasmic” astrocytes)
or long, thin processes for nerve fibers
(“fibrous” astrocytes)
Structural support of nerve fibers and cell bodies
Secretion and elimination of neurotransmitters
Chemical homeostasis
Oxygen and nutrient supply for neurons
Blood-brain barrier
Regulation of local blood flow
Oligodendrocytes
Schwann cells
Small cells with few processes
Myelin production; functions of myelin:
• increases the speed of nerve conduction by ten to
one hundred times;
• prevents loss of activation by ion diffusion and erratic
activation of adjacent axons
• Inhibition of the formation of new fibres for new
connection (reduction of plasticity);
• involved in learning and cognition.
Microglia
Resemble blood monocytes
Immune cells (phagocytosis of pathogens, cell debris)
the formation of new connections to match the number of outgrowing fibres to
the capacity of target cells (Lossi and Merighi 2003; Saxena and Caroni 2007).
The fittest neurons survive in competition for limited resources in the brain
as electrical impulses, neurotransmitters (e.g. nerve growth factor) and nutrients
within the neural network. Active cells with many connections to target cells re-
ceive more of these life-savers than less active neurons. Thus, overproduction
and subsequent elimination of excess neurons and connections are not a waste
of resources, but necessary to allow optimal locations and interconnections of
neurons.
Synapses are newly formed and eliminated throughout life. This allows contin-
uous reorganization of the neural network in accordance with the requirements
of the environment and is thus the basis of life-long neural development and
plasticity (Goda and Davis 2003). Between the onset of puberty and adult age ap-
proximately 40% of synapses and nerve fibres (Bourgeois 2002) and a substantial
portion of neurons are eliminated, particularly in the prefrontal cortex, the brain
region involved in major cognitive abilities. In accordance with the “use it or lose
it” principle, cells with apparently redundant connections for unused (not use-
less!) skills are discarded to enhance abilities that have been extensively utilized
(Lopez et al. 2008).
Adjustment of neurons and connections to the demands of the individual en-
vironment usually makes sense, but can result in severe impairments of sensory,
behavioural and cognitive functions, if the foetus or young infant is deprived
from normal sensory input or exposed to severe stress (Fabricius 2008). The hip-
pocampus (stores memory!) is particularly sensitive to the apoptotic actions of
14 Otwin Linderkamp et al.
corticosteroids transmitted to the foetus as a result of maternal stress (Fenoglio
et al. 2006).
References
Bergman K, Sarkar P, O’Connor TG, Modi N, Glover V (2007) Maternal stress during
pregnancy predicts cognitive ability and fearfulness in infancy. J Am Acad Child Ado-
lesc Psychiatry 46: 1454–1463
Berzhanskaya J, Ascoli G (2008) Computational neuroanatomy. Scholarpedia 3:1313
(www.scholarpedia.org)
Bourgeois JP (2002) Synaptogenesis in the neocortex of the newborn. in: Lagercrantz H,
Hanson M, Evrard P, Rodeck C (eds) The Newborn Brain. Cambridge University Press,
Cambridge, UK, pp 91–113
Colvert E, Rutter M, Kreppner J, Beckett C, Castle J, Groothues C, Hawkins A, Stevens
S, Sonuga-Barke EJ (2008) Do theory of mind and executive function deficits underlie
the adverse outcomes associated with profound early deprivation?: Findings from the
English and Romanian adoptees study. J Abnorm Child Psychol [Epub ahead of print]
De Graaf-Peters VB, Hadders-Algra M (2006) Ontogeny of the human central nervous
system: what is happening when? Early Hum Dev 82: 257–266
Eliot L (2000) What’s Going on in There? How the Brain and Mind Develop in the First
Five Years of Life. Bantam, New York, U.S.A.
Fabricius K, W¨ortwein G, Pakkenberg B (2008) The impact of maternal separation on adult
mouse behaviour and on the total neuron number in the mouse hippocampus. Brain
Struct Funct 212: 403–416
Fedor-Freybergh PG, Vogel LV (1988) Prenatal and Perinatal Psychology and Medicine:
Encounter With the Unborn. Parthenon, Carnforth, UK
Fenoglio KA, Brunson KL, Baram TZ (2006) Hippocampal neuroplasticity induced by
early-life stress: functional and molecular aspects. Front Neuroendocrinol 27: 180–192
Fields RD (2008) White matter in learning, cognition and psychiatric disorders. Trends
Neurosci [Epub ahead of print]
Ge S, Jang CH, Hsu KS, Ming GL, Song H (2007) A critical period for enhanced synaptic
plasticity in newly generated neurons of the adult brain. Neuron 54: 559–566
Gilbert G (2001) Individual Development and Evolution: The Genesis of Novel Behavior.
Lawrence Erlbaum Ass., Mahwah, NJ, U.S.A.
Goda Y, Davis GW (2003) Mechanisms of synapse assembly and disassembly. Neuron 40:
243–264
Gressens P (2005) Neuronal migration disorders. J Child Neurol 20: 969–971
Hansen D, Lou HC, Olsen J (2000) Serious life event and congenital malformations: a
national study with complete follow-up. Lancet 356: 975–980
H¨uther G, Krens I (2006) Das Geheimnis der ersten neun Monate. Unsere fr¨uhesten
Pr¨agungen. Walter, D¨usseldorf, Germany.
Janus L (2001) Enduring Effects of Prenatal Experiences. Mattes, Heidelberg, Germany.
Janus L (2007) Seelenraum des Ungeborenen: Pr¨anatale Psychologie und Therapie. Pat-
mos, D¨usseldorf, Germany.
Janus L, Linder R (2006) Psychologische und psychosomatische Aspekte von Schwanger-
schaft und Geburt. Prenat Perinat Psychol Med 18: 57–70
Kanold PO, Shatz CJ (2006) Subplate neurons regulate maturation of cortical inhibition
and outcome of ocular dominance plasticity. Neuron 51: 627–638
Khashan AS, Abel KM, McNamee R, Pedersen MG, Webb RT, Baker PN, Kenny LC,
Mortensen PB (2008) Higher risk of offspring schizophrenia following antenatal mater-
nal exposure to severe adverse life events. Arch Gen Psychiatry 65: 146–152
Time Table of Normal Foetal Brain Development 15
Kostovic I, Jovanov-Milosevic N (2006) The development of cerebral connections during
the first 20–45 weeks’ gestation. Semin Fetal Neonatal Med 11: 415–422
Lagercrantz H, Hanson M, Evrard P, Rodeck C (2002) The Newborn Brain. Neuroscience
and clinical applications. Cambridge University Press, Cambridge, UK
Linderkamp O (2005) Gehirnentwicklung bei Feten und Fr¨uhgeborenen, in: Fr¨uhgeborene
optimal ern¨ahren und pflegen, Frank C, Linderkamp O, Pohlandt F, pp. 126–131. Kirch-
heim, Mainz
Linderkamp O, Janus L, Linder R, Skoruppa D (2009a) Development of the foetal brain.
Genetics and experience-driven plasticity. Int J Prenat Perinat Psychol Med (in press)
Linderkamp O, Janus L, Linder R, Skoruppa D (2009b) Effects of prenatal stress on brain
development. Int J Prenat Perinat Psychol Med (in press)
Lopez B, Schwartz SJ, Prado G, Campo AE, Pantin H (2008) Adolescent neurological
development and its implications for adolescent substance use prevention. J Prim Prev
29: 5–35
Lossi L, Merighi A (2003) In vivo cellular and molecular mechanisms of neuronal apoptosis
in the mammalian CNS. Prog Neurobiol 69: 287–312
Maffei A, Nataraj K, Nelson SB, Turrigiano GG (2006) Potentiation of cortical inhibition
by visual deprivation. Nature 443: 81–84
Miller JH, McKinstry RC, Philip JV, Mukherjee P, Neil JJ (2003) Diffusion-tensor MR
imaging of normal brain maturation: a guide to structural development and myelina-
tion. Am J Roentgenol 180: 851–859
Mo Z, Moore AR, Filipovic R, Ogawa Y, Kazuhiro I, Antic SD, Zecevic N (2007) Human
cortical neurons originate from radial glia and neuron-restricted progenitors. J Neurosci
27: 4132–4145
Naves G, Cooke SF, Bliss TV (2008) Synaptic plasticity, memory and the hippocampus: a
neural network approach to causality. Nat Rev Neurosci 9: 65–75
Nicolic M, Reynolds R (2008) Mechanisms governing neuronal migration and morphology.
Dev Neurosci 30: 1–222
Perkins L, Hughes E, Srinivasan L, Allsop J, Glover A, Kumar S, Fisk N, Rutherford M
(2008) Exploring cortical subplate evolution using magnetic resonance imaging of the
fetal brain. Dev Neurosci 30: 211–220
Petanjek Z, Judas M, Kostovic I, Uylings HB (2008) Lifespan alterations of basal dendritic
trees of pyramidal neurons in the human prefrontal cortex: a layer-specific pattern.
Cereb Cortex 18: 915–929
Plomin R, Spinath FM (2004) Intelligence: Genetics, genes, and genomics. J Personal Soc
Psychol 86: 112–129
Rakic P (2003) Developmental and evolutionary adaptations of cortical radial glia. Cereb
Cortex 13: 541–549
Ridgway R, House SH (2006) The Unborn Child. Beginning a Whole Life and Overcoming
Problems of Early Origin. Karnac, London, UK
Ridley M (2003) Nature via Nurture. Genes, Experience and What Makes us Human.
Harper Collins, London
Rutter M (2006) Genes and Behavior: Nature-Nurture Interplay Explained. Blackwell,
Cambridge, MA
Saxena S, Caroni P (2007) Mechanisms of axon degeneration: from development to disease.
Prog Neurobiol 83: 174–191
Turkewitz G (2007) The relevance of the fetal and neonatal period for the development
of novelty preferences, learning, habituation and hemispheric specialization. Dev Psy-
chobiol 49: 780–787
16 Otwin Linderkamp et al.
Uylings HB, Malofeeva LI, Bogolepova IN, Jacobsen AM, Amunts K, Zilles K (2005) No
postnatal doubling of number of neurons in human Broca’s areas (Brodmann areas 44
and 45)? A stereological study. Neuroscience 136: 715–728
Van den Bergh BR, Van Calster B, Smits T, Van Huffel S, Lagae L (2008) Antenatal mater-
nal anxiety is related to HPA-axis dysregulation and self-reported depressive symptoms
in adolescence: A prospective study on the fetal origins of depressed mood. Neuropsy-
chopharmacology 33: 536–545
Volpe JJ (2008) Neurology of the Newborn, 5th ed. Saunders Co., Philadelphia
Waites CL, Craig AM, Garner CC (2005) Mechanisms of vertebrate synaptogenesis. Annu
Rev Neurosci 28: 251–274
Zhang CL, Zou Y, He W, Gage FH, Evans RM (2008) sA role for adult TLX positive
neural stem cells in learning and behaviour. Nature 451: 1004–1007
Correspondence to: Otwin Linderkamp, Prof. Dr., Kornmarkt 3, 69117 Heidelberg, Ger-
many, E-Mail olinderkamp@yahoo.de

More Related Content

PDF
Developmental reorganization of the human cerebral cortex
PDF
Akhtar and Breunig-2015-Frontiers in Cellular Neuroscience - Barriers to post...
PDF
Glial cells and astrocytes: neural networks modulators?
PDF
Neuroscience in the 21st century
PDF
Neural Differentiation
PPTX
Plasticity of the brain - VCE U4 Psychology
PDF
Case record...Cortical/cerebellar dysplasia
PPTX
Neural crest ( surgical point of view )
Developmental reorganization of the human cerebral cortex
Akhtar and Breunig-2015-Frontiers in Cellular Neuroscience - Barriers to post...
Glial cells and astrocytes: neural networks modulators?
Neuroscience in the 21st century
Neural Differentiation
Plasticity of the brain - VCE U4 Psychology
Case record...Cortical/cerebellar dysplasia
Neural crest ( surgical point of view )

What's hot (12)

PDF
Neurodesarrollo - Migración neuronal
PPT
Development
PPTX
Neural crest cells in 2 parts / dental implant courses by Indian dental academy 
PDF
Stem cells Used to Develop Mini Human Brain & Stem Cells for Spinal Cord Inju...
PPTX
Neural crest cells / dental implant courses by Indian dental academy 
PPTX
Fetal brain development and cellular functions
PDF
Umbilical Cord Blood Cells and Brain Stroke Injury - Cryoviva India
PDF
Adult Neurogenesis and it's Role in Alzheimer's
PDF
Liang_Shiochee_ArestyPoster_FINAL
PPTX
Brain development
PDF
A ‘neural’ net that can be seen with the naked eye - by Andrew Packard
PPT
Neural crest cell
Neurodesarrollo - Migración neuronal
Development
Neural crest cells in 2 parts / dental implant courses by Indian dental academy 
Stem cells Used to Develop Mini Human Brain & Stem Cells for Spinal Cord Inju...
Neural crest cells / dental implant courses by Indian dental academy 
Fetal brain development and cellular functions
Umbilical Cord Blood Cells and Brain Stroke Injury - Cryoviva India
Adult Neurogenesis and it's Role in Alzheimer's
Liang_Shiochee_ArestyPoster_FINAL
Brain development
A ‘neural’ net that can be seen with the naked eye - by Andrew Packard
Neural crest cell
Ad

Similar to Time table of normal foetal brain development (20)

PPT
Brain development
PPT
Development of Central Nervous system in Child
PPTX
chapter7.pptx
PPT
chapter7.ppt
PPT
Pinel basics ch07
PPTX
Preterm growth and development
PPTX
Basics of Embryology and short review of congenital errors of CNS in radiolog...
PPTX
Development of Central nervous system ppt
PPTX
gestational period: germinal, embryonic, and fetal.
PPT
Life span chapter 3
PDF
Lesson presentation on Infancy and Toddlerhood.pdf
PPTX
Development of central nervous system
PPT
The Brain
PPTX
Brain Development
PPT
CNS Development
PPTX
PSY 150 403 CHAPTER 4 SLIDES
PPTX
1. Introduction to Module.pptx
PPT
Development_ppt2.ppt
PPT
Healthy Beginnings
PPT
Lecture3 psych125 bunge
Brain development
Development of Central Nervous system in Child
chapter7.pptx
chapter7.ppt
Pinel basics ch07
Preterm growth and development
Basics of Embryology and short review of congenital errors of CNS in radiolog...
Development of Central nervous system ppt
gestational period: germinal, embryonic, and fetal.
Life span chapter 3
Lesson presentation on Infancy and Toddlerhood.pdf
Development of central nervous system
The Brain
Brain Development
CNS Development
PSY 150 403 CHAPTER 4 SLIDES
1. Introduction to Module.pptx
Development_ppt2.ppt
Healthy Beginnings
Lecture3 psych125 bunge
Ad

More from BARRY STANLEY 2 fasd (20)

PDF
Response to "Winter Formal"
PDF
2 the mcmechan reservoir development
PDF
Mansfield Mela.scholar.google.ca
PDF
The Nomenclature of the Consequences of Prenatal Alcohol Exposure: PAE, and t...
PDF
Aqua study updates | murdoch children's research institute
PDF
Effects of Hyperbaric Oxygen Therapy on Brain Perfusion, Cognition and Behavi...
PDF
Landmark legislation a victory for the fasd community
PDF
Four year follow-up of a randomized controlled trial of choline for neurodeve...
PDF
The Resting State and its Default Mode: in those with FASD
PDF
Australia and new zealand are showing the way to canada
PDF
Work requirements for individuals with fasd, in the time of covid 19
PDF
Covid 19 and alcohol
PDF
Association Between Prenatal Exposure to Alcohol and Tobacco and Neonatal Bra...
PDF
New insight on maternal infections and neurodevelopmental disorders: mouse st...
PDF
PDF
Clinical course and risk factors for mortality of adult inpatients with covid...
PDF
Preconceptual alcohol and the need for a diagnostic classification of alcoho...
PDF
The importance and significance of the diagnosis the personal testimony of r...
PDF
Parallel Tracks
PDF
Preconceptual alcohol
Response to "Winter Formal"
2 the mcmechan reservoir development
Mansfield Mela.scholar.google.ca
The Nomenclature of the Consequences of Prenatal Alcohol Exposure: PAE, and t...
Aqua study updates | murdoch children's research institute
Effects of Hyperbaric Oxygen Therapy on Brain Perfusion, Cognition and Behavi...
Landmark legislation a victory for the fasd community
Four year follow-up of a randomized controlled trial of choline for neurodeve...
The Resting State and its Default Mode: in those with FASD
Australia and new zealand are showing the way to canada
Work requirements for individuals with fasd, in the time of covid 19
Covid 19 and alcohol
Association Between Prenatal Exposure to Alcohol and Tobacco and Neonatal Bra...
New insight on maternal infections and neurodevelopmental disorders: mouse st...
Clinical course and risk factors for mortality of adult inpatients with covid...
Preconceptual alcohol and the need for a diagnostic classification of alcoho...
The importance and significance of the diagnosis the personal testimony of r...
Parallel Tracks
Preconceptual alcohol

Recently uploaded (20)

PDF
Lecture on Anesthesia for ENT surgery 2025pptx.pdf
PPTX
ANESTHETIC CONSIDERATION IN ALCOHOLIC ASSOCIATED LIVER DISEASE.pptx
PPTX
Vaccines and immunization including cold chain , Open vial policy.pptx
PPT
nephrology MRCP - Member of Royal College of Physicians ppt
PPT
neurology Member of Royal College of Physicians (MRCP).ppt
PPTX
Impression Materials in dental materials.pptx
PPT
Blood and blood products and their uses .ppt
PDF
SEMEN PREPARATION TECHNIGUES FOR INTRAUTERINE INSEMINATION.pdf
PPTX
Approach to chest pain, SOB, palpitation and prolonged fever
PPTX
thio and propofol mechanism and uses.pptx
PPTX
HYPERSENSITIVITY REACTIONS - Pathophysiology Notes for Second Year Pharm D St...
PDF
OSCE Series ( Questions & Answers ) - Set 6.pdf
PPTX
Neoplasia III.pptxjhghgjhfj fjfhgfgdfdfsrbvhv
PDF
Glaucoma Definition, Introduction, Etiology, Epidemiology, Clinical Presentat...
PPT
Infections Member of Royal College of Physicians.ppt
PPTX
Wheat allergies and Disease in gastroenterology
DOCX
PEADIATRICS NOTES.docx lecture notes for medical students
PPTX
NRP and care of Newborn.pptx- APPT presentation about neonatal resuscitation ...
PDF
Lecture 8- Cornea and Sclera .pdf 5tg year
PPTX
SHOCK- lectures on types of shock ,and complications w
Lecture on Anesthesia for ENT surgery 2025pptx.pdf
ANESTHETIC CONSIDERATION IN ALCOHOLIC ASSOCIATED LIVER DISEASE.pptx
Vaccines and immunization including cold chain , Open vial policy.pptx
nephrology MRCP - Member of Royal College of Physicians ppt
neurology Member of Royal College of Physicians (MRCP).ppt
Impression Materials in dental materials.pptx
Blood and blood products and their uses .ppt
SEMEN PREPARATION TECHNIGUES FOR INTRAUTERINE INSEMINATION.pdf
Approach to chest pain, SOB, palpitation and prolonged fever
thio and propofol mechanism and uses.pptx
HYPERSENSITIVITY REACTIONS - Pathophysiology Notes for Second Year Pharm D St...
OSCE Series ( Questions & Answers ) - Set 6.pdf
Neoplasia III.pptxjhghgjhfj fjfhgfgdfdfsrbvhv
Glaucoma Definition, Introduction, Etiology, Epidemiology, Clinical Presentat...
Infections Member of Royal College of Physicians.ppt
Wheat allergies and Disease in gastroenterology
PEADIATRICS NOTES.docx lecture notes for medical students
NRP and care of Newborn.pptx- APPT presentation about neonatal resuscitation ...
Lecture 8- Cornea and Sclera .pdf 5tg year
SHOCK- lectures on types of shock ,and complications w

Time table of normal foetal brain development

  • 1. Int. J. Prenatal and Perinatal Psychology and Medicine Vol. 21 (2009) No. 1/2, pp. 4–16 Time Table of Normal Foetal Brain Development Otwin Linderkamp, Ludwig Janus, Rupert Linder, and Dagmar Beate Skoruppa Abstract: The foetal brain develops within few weeks from a thin cell layer to a gigantic and complex network with billions of neurons and trillions of connections. This process is influenced by environmental factors (e.g. maternal stress) from the beginning. Under- standing of the developmental processes is the basis of prenatal medicine and psychology. Five steps can be related to fairly defined time periods: (1) From 7 to 22 weeks of gestation 20 billion neurons are produced and migrate to their final locations in the brain. (2) From 20 to 35 weeks the transient subplate structure lays the foundation of the cortex. (3) The organization of the neural network (nerve fibre and synapse formation) starts at 24 weeks gestation and continues throughout life. (4) Individual adjustment of the neural network by elimination of more than 50% of the neurons and circuits also starts at 24 weeks, and shapes the brain in three waves. (5) Myelination of axons begins during the last weeks of gestation and continues for decades. Keywords: cortex, gestational age, neuron, prenatal, subplate, synapse Introduction During the last twenty years, foetal brain development has become an essen- tial topic of neuroscience as a result of modern non-invasive and computational techniques and animal models. The results allow quantitative description of the structure and development of individual nerve cells and entire networks within specific brain areas, and to relate the structures to the functions at both the sin- gle neuron and network levels (Berzhanskaya and Ascoli 2008). Recent results support the hypotheses of publications on prenatal psychology emphasizing the importance of environment and experience for the normal psychological devel- opment of the foetus (Fedor-Freybergh and Vogel 1988; Janus 2001, 2007; Janus and Linder 2006; Ridgeway and House 2006). Several reviews on foetal brain development appeared during the last years (De Graaf-Peters and Hadders-Algra 2006; Eliot 2000; Gilbert 2001; H¨uther and Krens 2006; Lagercrantz et al. 2002; Linderkamp 2005; Ridley 2003; Rutter 2006; Turkewitz 2007). Our present review is designed to summarize the present knowl- edge of foetal brain development with emphasis on the time-table of the events shaping the brain. Our paper provides the basis of understanding experience- dependent brain development and effects of maternal anxiety and stress on the brain and long-term outcome. Subsequent papers of our group will focus on these topics (Linderkamp et al. 2010a, b).
  • 2. Time Table of Normal Foetal Brain Development 5 Early Human Brain Development The brain development begins at approximately three weeks after conception (5 weeks of gestation) with the formation of the neural plate at the back of the embryo. A few days later the plate folds to form the neural tube around a canal. In the brain the canal later widens to the ventricles, in the spinal cord it forms the central canal. At the time of neural tube closure the neural wall consists of one or two layers of epithelial cells (neuroepithelium) which are the precursors of an enormous variety of neurons and the macroglia. The development of the cerebral cortex occurs in precisely-timed stages (Table 1, Fig. 1). Each developmental process is also a vulnerable period which is sensitive to environmental insults rendering the brain susceptible to structural malformations and functional impairments. 10 15 20 25 30 35 40 6 12 24 4 8 16 32 Neurulation Neural proliferation Neuronal migration Subplate neurons Axon growth Synapse formation Glia proliferation Myelination Neuronal death Fibre retraction Synapse elimination 10 15 20 25 30 35 40 6 12 24 4 8 16 32 months years Postnatal Age weeks Gestational Age Fig. 1. Time table of developmental events of the human brain during foetal and postnatal life. Black shaded areas indicate peak activities, open lined areas indicate low or medium activity. Neurogenesis: “Raw Material” for the Brain Billions of nerve cells (neurons) are produced during the development of the cen- tral nervous system. Neurogenesis mainly occurs at the inner edge of the neural tube wall, the later ventricles (brain) and central canal (spinal cord), respectively (Fig. 2). In preterm infants the reproduction zone is still visible on ultrasound scans (“subependymal germinal matrix”). Cell division begins once the neural
  • 3. 6 Otwin Linderkamp et al. Table 1. Major events in foetal cortical development. Peak occurrence* Major developmental events Abnormal development 5-9 wk Primary neurulation (neural tube formation) Prosencephalon formation (precursor of haemispheres) Anencephaly Encephalocele** Meningomyelocele Spina bifida** 12-18 wk (6 wk to life long) Neuronal proliferation (neurogenesis) Encephalocele, microbrain** Schizophrenia** 12-20 wk (8-30 wk) Neuronal migration Formation of cortical cell layers Heterotopias (wrong place); reduced or no gyration: reduced attention and cognition, depressive signs** 22-34 wk (15-38 wk) Subplate neurons (guidance of axons between thalamus, cortex and subcortical structures; final migration of neurons) Impaired development of thalamus and cortex and connecting circuits: disorders of frontal, temporal and parietal centers** 24 wk to 15 mo (10 wk to life-long) Outgrowth of axons Outgrowth of dendrites Synaptogenesis White matter reduction Cortical dysplasias: Down, fragile-X syndrome sensory, behavioural, cognitive disorders** 24-38 wk (20-44 wk) 24 wk to life-long Selective death of neurons Elimination of synapses Excessive loss of neurons and connecting circuits: cognitive, sensory, behavioural, psychiatric disorders** 15 wk to 18 mo (6 wk to life-long) Glial cells proliferate und differentiate (structural support, neuronal migration, myelin, “clean up”) Impaired neuronal migration Loss of dendrites and synapses in frontal cortex, hippocampus, amygdale 35 wk to 24 mo (15 wk to adulthood) Myelination Dysfunction of axons: psychiatric, cognitive disorders** Abbreviatons: IQ, intelligence quotient; p.n., mo, months postnatal; wk, weeks gestation *Gestational (postmenstrual) age; in parentheses, occurrence prolonged at slower pace. **Increased risk due to maternal stress has been shown in human foetuses or animal models (from Linderkamp et al. 2010b). tube has closed at 4 to 5 weeks after conception (6 to 7 weeks of gestation). The majority of neurons are formed at 12 to 18 weeks of gestation. Approximately 100 000 neurons are produced during each second to provide a number of at least 200 billion (2 × 1011) neurons in the human brain and 40 billion in the neocortex alone. Approximately 50% of the neurons are eliminated during the later mat- uration process, resulting in a final number of 100 billion neurons at 40 weeks (full-term). Proliferation of neurons during the first 22 weeks of gestation is mainly deter- mined by genetic factors (Bourgois 2002). However, severe maternal stress during the first trimester (i.e. neurulation and early neurogenesis) has been linked to an increased risk of encephalocele (Hansen et al. 2000) and schizophrenia (Khashan et al. 2008), suggesting that the expression of genes in early foetal life is influ- enced by external factors. Stress-induced reduction of neurons in late foetal life is probably the result of increased damage of neurons (Fabricius et al. 2008).
  • 4. Time Table of Normal Foetal Brain Development 7 Fig. 2. Section through the cortex at approximately 24 weeks of gestation. Note that the germinal zone adjoins to the ventricle at the inner edge of the cortex. Newly formed neu- rons migrate along the radial glia through the subplate and previously formed neuronal layers to the upper layer of the cortical plate. If the brain is sufficiently used and trained, new neurons are generated through- out life. Neural stem cells and pluripotent radial glia cells are able to differentiate into neurons in the adult brain (Mo et al. 2007). In mice, neurogenesis increased the efficiency of learning, but did not affect long-term memory (Zhang et al. 2008). The formation of new synapses and the prevention of neuronal damage are far more important mechanisms for life-long learning than the formation of new neurons (Uylings et al. 2005). Migration of Neurons: Finding the Right Place After several divisions neuroblasts lose their ability to divide and they begin to move away from the inner multiplication zone to the outer edges of the growing neural tube wall. Once a neuron has reached its final destination within the correct cortical layer, it will stay there for life. The first neurons start migration with the beginning of multiplication, the majority of cells move to their layer between 12 and 20 weeks of gestation (Gressens 2005). Both passive pushing by subsequently migrating neurons and active movement of neurons are mechanisms of migration. In the cortex, neurons move radially outwards to the surface along specialized radial glial fibres (Fig. 2), which span the entire thickness of the hemisphere from the ventricular surface to the external pial surface (Rakic 2003). This “ladder” facilitates the journey through the earlier arriving cell layers. At the brain surface, the neurons leave the ladder and move
  • 5. 8 Otwin Linderkamp et al. Table 2. Maturation of nerve cells in the cortex. Step Events Neurogenesis Subventricular stem cells divide symmetrically. The last division results in larger neurons before they migrate. Radial glia Generated from same stem cells a neurons. Form long processes through the entire cortex (fig. 2). Migration Neurons climb on radial glia to cortical surface. Contact to subplate neurons Migration through subplate neurons (fig. 2) and contact to thalamo-cortical and cortico-cortical fibres may accelerate their maturation. Formation of six cortical layers Neurons migrate through previously formed layers to the surface. Thus, the early-migrating cells form the superficial layer, the latest the deepest until six cortical layers have been established. Neurons assemble in columns above the stem cells and are therefore clonally related. Astrocyte formation Astrocytes are generated from radial glia. Life-long neurogenesis New neurons are generated from remaining subventricular stem cells and locally from radial glia. laterally to give way to the subsequently arriving neurons and to form a layer at the surface of the cortex. Then the next group of migrating cells passes through this layer and forms a new layer at the surface. This process continues until six layers have been formed. Thus, the earlier generated neurons form the deepest cortical layer, and the latest cells settle in the most superficial layer (inside-out order). The radial migration of neurons originating from the same reproduction site results in columns of clonally related cells. This may be important for their specialized functions in their final cortical destination. Insufficient movement or migrations to wrong places result in heterotopias which may be associated with serious malformations as lissencephaly (reduced gyration, “flat brain”), epilepsy and mental retardation (Gressens 2005; Nicolic and Reynolds 2008). Although normal migration of neurons to the right location is probably determined by genes (Rutter 2006), abnormal migration is mostly the result of environmental factors. Maternal stress during the gestational age of max- imal neuronal migration has been shown to predispose the offspring to a variety of impairments including reduced attention span, cognitive problems and depressive symptoms (van den Bergh et al. 2008). Organisation of the Neural Network The first two steps, multiplication and migration of primitive nerve cells, are mostly completed at 22 weeks of gestation. At the beginning of migration neurons are not yet specialized, but they lose their pluripotency once they have reached their final position in a specialized region of the central nervous system. Organization of an individual neuron refers to the establishment of connec- tions with other cells and the specialization to distinct functions within the neural network. Organization of the total central nervous system refers to the formation of the entire neuronal network and its capacity to operate as an integrated whole.
  • 6. Time Table of Normal Foetal Brain Development 9 Table 3. Major steps of neural organisation of the cortex (modified from Volpe 2008). Goal: Establishment of a functioning neural network Major period: 20 weeks of gestation to years after birth Steps: • Formation of subplate neurons with initial fibre and synapse formation. • Formation of the cortical plate with six layers of aligned neurons. • Outgrowth of nerve fibres (axons, dendrites) and their ramifications. • Synptogenesis. • Selective elimination of neurons (apoptosis), nerve fibres and synapses. • Proliferation and differentiation of neuroglia. The process of organization starts at approximately 22 weeks of gestation and includes actions of subplate neurons, outgrowth of neural fibres, synaptogenesis and myelination. Subplate Neurons: Pioneers Paving the Wire Tracks Subplate neurons play a major role in the development of the gigantic network connecting billions of neurons and are probably responsible for the evolution of the neocortex. The subplate zone is situated between the intermediate zone (pre- cursor of white matter) and the cortical plate with the six layers of neurons (Fig. 2). In magnetic resonance images, the subplate is visible as a continuous band in the entire cortex at 20–27 weeks of gestation, starts to disappear in the parietal lobe at 28 weeks, but remains prominent in the frontal lobe up to 35 weeks (Perkins et al. 2008). At 38 weeks, 90% of the subplate neurons have disappeared. The subplate neurons excrete neurotransmitters that attract axons ascending from the thalamus and dendrites descending from cortical neurons for transient connections with the subplate neurons. When the subplate neurons die, the tha- lamic and cortical neurons become directly connected (thalamo-cortical tracts). Moreover, subplate neurons help cortical neurons to establish connections with other cortical neurons in both hemispheres and to guide the final migration of cortical neurons within the six layers. They help to balance excitation and inhi- bition in cortical layers, which is important for the “plasticity” of brain functions (Kanold and Shatz 2006). The transient connections among various brain cen- tres via subplate neurons are the basis for early foetal (and preterm’s) behaviour (Kostovics and Jovanov-Milosevic 2006). Maternal stress during the peak actions of subplate neurons from 22 to 34 weeks gestation has been linked to developmental delays, lower IQ, behavioural problems and schizophrenia in offsprings (Bergman et al. 2007). It is likely that the stress exposure of preterm infants during intensive care can alter subplate neurons, thereby contributing to the high risk of preterm infants to long-term cognitive and behavioural problems.
  • 7. 10 Otwin Linderkamp et al. Wiring the Neural Network: Axons, Dendrites and Synapses The set-up of a functioning neural network connecting all parts of the central nervous system and other target organs requires trillions of connections among neurons via axons, dendrites and synapses. The migrating cells have no function- ing axons and dendrites. Having migrated to the appropriate position, axons and dendrites begin to grow out of the young neurons. Usually one axon only arises from each cell (Fig. 3). Axons are the long nerve fibres connecting distant parts within the central nervous system and with pe- ripheral organs (e.g. muscles and glands). Their final length can be more than a meter in adults, but also just a few µm, if they connect adjacent neurons. Ax- ons develop many branches at the tip and each final branch can form a synapse with a final branch of a dendrite or sometimes another axon or a nerve cell body. Dendrites emerge from many points along the cell body and appear very much like branches on a tree. Axons and dendrites find their target cells principally by growing in the direction of the targets. This growth is guided by molecules bound to cells (for short-range chemoattraction) or diffused in the environment (long-range chemoattraction, e.g. nerve growth factor). Target cells also present and secrete chemorepellents that inhibit the growth of connecting nerve fibres to these cells. The search of outgrowing fibres for target neurons can be highly specific or more or less arbitrary. Specific connections are formed between neu- rons that express specific marker molecules, thereby giving the connecting cells no choice (cell specificity). Other neurons are attracted to send fibres to neurons in a defined region (topographic specificity). Synapses are formed by proteins acting as molecular switches between two nerve fibres. Chemoattractants determine when and where synapses are formed and their specificity and stability. Moreover, formation, specificity and stability of a synapse depend on the quality and quantity of impulses travelling through the con- necting fibres. Synaptic activity provides critical information about the usefulness of synaptic connections, thereby influencing synapse stability and maintenance (Waites et al. 2005). Synaptic activity promotes the formation of new synapses and strengthens existing synapses in the neighbourhood. Thus, synapse formation and stabilization are dynamic processes, requiring bi-directional communication between connected partners. Subtle alterations in synaptic connections are the means by which learning wires the pathways to memory (Ge et al. 2007). Although the first synapses are produced already at 8 weeks of gestation, synapse formation is slow until 24 weeks of gestation resulting in a total num- ber of synapses that is not much higher than the total number of neurons. From 24 weeks gestation to 12 months of postnatal age, a myriad of connections is formed among billions of neurons. At full-term each cortical neuron is linked with approximately 2500 other neurons, at 12 months of postnatal age with 15 000 (Petanjek et al. 2008). Synaptogenesis begins in a relatively short time period in all cortical regions, but the maximum synaptic density is reached at different times after full-term, ranging from 3 months in the auditory and visual cortex to 15 months in the prefrontal cortex (Bourgeois 2002). After the first year of postnatal life the total synapse number slowly increases and reaches the maximum at five years when the child’s brain weighs almost as much as in adults. Then the number of synapses plateaus until about 10 years and
  • 8. Time Table of Normal Foetal Brain Development 11 Fig. 3. Neurons with one axon and several dendrites arising from the neuronal cell body. The left neuron represents the development in the sensory cortex at approximately 24– 28 weeks, the right neuron at 32–40 weeks. Note the marked differences in ramifications between the two neurons. begins to decrease by approximately 40% with the onset of puberty. Thus, dur- ing the first 5–10 years of life, the child achieves the highest number of synapses, thereby enabling the child to acquire enormous behavioural, social, environmen- tal, linguistic and cultural information. After the age of five years, synaptogenesis continues as a local event (Bourgeois 2002) in dependence on the activity of neighbouring synapses. Formation of new synapses and changes of specificity and stability of synapses are fundamental to life-long learning, memory and cognition in the mature brain (Waites et al. 2005). Outgrowth of fibres and formation of synapses are largely influenced by envi- ronmental factors, including sensory experience. Both decreased sensory input of the foetus and maternal stress may cause a marked reduction of axons, dendrites and synapses in the prefrontal cortex, the hippocampus and other brain centres (Linderkamp et al. 2010b). Glial Cells and Myelination Glial cells (also called neuroglia) are non-neuronal cells that outnumber neu- rons by about 10 to 1, but constitute only half of the brain volume, since they are smaller than neurons. Glial cells surround neurons and hold them in place, play an important role in neuronal and axonal guidance, supply nutrients and oxygen to neurons, produce and remove chemical transmitters, insulate axons by myelin,
  • 9. 12 Otwin Linderkamp et al. destroy pathogens, dead neurons and other debris, and contribute to formation of new neurons. Glial cells are crucial in the development of the nervous system and in processes such as synaptic plasticity and synaptogenesis. Various types of glial cells are defined by origin, appearance and functions (Table 4). Macroglial cells comprise radial glia, astrocytes and oligodendrocytes and de- velop from the same stem cells in the ventricular zone of the neural tube as the neurons. Radial glia cells are the progenitors of astrocytes, some oligodendro- cytes and neurons. In the developing brain, radial glia functions as a “ladder” upon which neurons migrate to the surface of the cortex. Microglia are special- ized immune cells capable of phagocytosis. They are derived from haemopoietic precursors as other immune cells. Oligodendrocytes produce myelin that forms insulating sheaths around axons. Schwann cells provide myelination to axons in the peripheral nervous system. Myelin is a white fatty material wrapped around most neural axons. It prevents the leakage of ions and thus of electrical current from the axon, thereby increasing the speed of nerve conduction by ten to one hundred times. Moreover, myelin pre- vents erratic activation of adjacent axons. Without myelin, electric activity would be aimlessly distributed throughout the brain, and information would become chaotic. Myelination also inhibits plasticity, since a myelinated axon has less abil- ity to branch out and connect with other neurons. Myelin is involved in cognitive functions and learning (Fields 2008). Myelination starts in the spinal cord (at about 12 weeks gestation), then in brain stem (14 weeks) and thalamic axons (20 weeks), and finally in the cortex (35 weeks) and continues for decades in the human brain (Miller et al. 2003). Axons connecting the frontal-limbic system (responsible for complex cognitive functions) start to myelinate after birth. Late myelination explains that the brains of infants and young children are slow compared with adult brains. Myelination is modifiable by experience and severe maternal or postnatal stress may inhibit myelination, thereby contributing to psychiatric disorders, including schizophre- nia and depression, and cognitive impairment (Fields 2008). Shaping the Brain by Elimination of Excess Neurons and Circuits At least twice as many neurons as necessary are produced during the time period of active neuronal multiplication, and most of the excess neurons are eliminated during maturation of the neuronal network (“programmed cell death” or apop- tosis). Three peak periods of neuronal death can be distinguished (Fig. 1): 1) at the beginning of neurogenesis; 2) from 24 to 38 weeks gestation; and 3) between the onset of puberty and adulthood (Lossi and Merighi 2003). The second and third periods are linked to selective elimination of axons, den- drites and synapses. Production of neurons and growth of axons and dendrites in the direction of target cells are not very selective and result in overproduction of connections. The initial wiring is diffuse, with a lot of overlap making commu- nication inaccurate and disorganized. Elimination of fibres, synapses and entire neurons allows quantitative adjustments of connections between neurons and to compensate for errors of cell migration (mislocation) and projection of axons and dendrites (misprojection). Elimination of neurons, fibres and synapses parallels
  • 10. Time Table of Normal Foetal Brain Development 13 Table 4. Glial cells. Cell type Structure Functions Radial glia Long radial processes spanning the thickness of the cortical wall Progenitors of neurons and astrocytes Guidance of neurons and nerve fibers Regulation of synaptic plasticity Astrocytes Support cells with short, thick processes for neurons (“protoplasmic” astrocytes) or long, thin processes for nerve fibers (“fibrous” astrocytes) Structural support of nerve fibers and cell bodies Secretion and elimination of neurotransmitters Chemical homeostasis Oxygen and nutrient supply for neurons Blood-brain barrier Regulation of local blood flow Oligodendrocytes Schwann cells Small cells with few processes Myelin production; functions of myelin: • increases the speed of nerve conduction by ten to one hundred times; • prevents loss of activation by ion diffusion and erratic activation of adjacent axons • Inhibition of the formation of new fibres for new connection (reduction of plasticity); • involved in learning and cognition. Microglia Resemble blood monocytes Immune cells (phagocytosis of pathogens, cell debris) the formation of new connections to match the number of outgrowing fibres to the capacity of target cells (Lossi and Merighi 2003; Saxena and Caroni 2007). The fittest neurons survive in competition for limited resources in the brain as electrical impulses, neurotransmitters (e.g. nerve growth factor) and nutrients within the neural network. Active cells with many connections to target cells re- ceive more of these life-savers than less active neurons. Thus, overproduction and subsequent elimination of excess neurons and connections are not a waste of resources, but necessary to allow optimal locations and interconnections of neurons. Synapses are newly formed and eliminated throughout life. This allows contin- uous reorganization of the neural network in accordance with the requirements of the environment and is thus the basis of life-long neural development and plasticity (Goda and Davis 2003). Between the onset of puberty and adult age ap- proximately 40% of synapses and nerve fibres (Bourgeois 2002) and a substantial portion of neurons are eliminated, particularly in the prefrontal cortex, the brain region involved in major cognitive abilities. In accordance with the “use it or lose it” principle, cells with apparently redundant connections for unused (not use- less!) skills are discarded to enhance abilities that have been extensively utilized (Lopez et al. 2008). Adjustment of neurons and connections to the demands of the individual en- vironment usually makes sense, but can result in severe impairments of sensory, behavioural and cognitive functions, if the foetus or young infant is deprived from normal sensory input or exposed to severe stress (Fabricius 2008). The hip- pocampus (stores memory!) is particularly sensitive to the apoptotic actions of
  • 11. 14 Otwin Linderkamp et al. corticosteroids transmitted to the foetus as a result of maternal stress (Fenoglio et al. 2006). References Bergman K, Sarkar P, O’Connor TG, Modi N, Glover V (2007) Maternal stress during pregnancy predicts cognitive ability and fearfulness in infancy. J Am Acad Child Ado- lesc Psychiatry 46: 1454–1463 Berzhanskaya J, Ascoli G (2008) Computational neuroanatomy. Scholarpedia 3:1313 (www.scholarpedia.org) Bourgeois JP (2002) Synaptogenesis in the neocortex of the newborn. in: Lagercrantz H, Hanson M, Evrard P, Rodeck C (eds) The Newborn Brain. Cambridge University Press, Cambridge, UK, pp 91–113 Colvert E, Rutter M, Kreppner J, Beckett C, Castle J, Groothues C, Hawkins A, Stevens S, Sonuga-Barke EJ (2008) Do theory of mind and executive function deficits underlie the adverse outcomes associated with profound early deprivation?: Findings from the English and Romanian adoptees study. J Abnorm Child Psychol [Epub ahead of print] De Graaf-Peters VB, Hadders-Algra M (2006) Ontogeny of the human central nervous system: what is happening when? Early Hum Dev 82: 257–266 Eliot L (2000) What’s Going on in There? How the Brain and Mind Develop in the First Five Years of Life. Bantam, New York, U.S.A. Fabricius K, W¨ortwein G, Pakkenberg B (2008) The impact of maternal separation on adult mouse behaviour and on the total neuron number in the mouse hippocampus. Brain Struct Funct 212: 403–416 Fedor-Freybergh PG, Vogel LV (1988) Prenatal and Perinatal Psychology and Medicine: Encounter With the Unborn. Parthenon, Carnforth, UK Fenoglio KA, Brunson KL, Baram TZ (2006) Hippocampal neuroplasticity induced by early-life stress: functional and molecular aspects. Front Neuroendocrinol 27: 180–192 Fields RD (2008) White matter in learning, cognition and psychiatric disorders. Trends Neurosci [Epub ahead of print] Ge S, Jang CH, Hsu KS, Ming GL, Song H (2007) A critical period for enhanced synaptic plasticity in newly generated neurons of the adult brain. Neuron 54: 559–566 Gilbert G (2001) Individual Development and Evolution: The Genesis of Novel Behavior. Lawrence Erlbaum Ass., Mahwah, NJ, U.S.A. Goda Y, Davis GW (2003) Mechanisms of synapse assembly and disassembly. Neuron 40: 243–264 Gressens P (2005) Neuronal migration disorders. J Child Neurol 20: 969–971 Hansen D, Lou HC, Olsen J (2000) Serious life event and congenital malformations: a national study with complete follow-up. Lancet 356: 975–980 H¨uther G, Krens I (2006) Das Geheimnis der ersten neun Monate. Unsere fr¨uhesten Pr¨agungen. Walter, D¨usseldorf, Germany. Janus L (2001) Enduring Effects of Prenatal Experiences. Mattes, Heidelberg, Germany. Janus L (2007) Seelenraum des Ungeborenen: Pr¨anatale Psychologie und Therapie. Pat- mos, D¨usseldorf, Germany. Janus L, Linder R (2006) Psychologische und psychosomatische Aspekte von Schwanger- schaft und Geburt. Prenat Perinat Psychol Med 18: 57–70 Kanold PO, Shatz CJ (2006) Subplate neurons regulate maturation of cortical inhibition and outcome of ocular dominance plasticity. Neuron 51: 627–638 Khashan AS, Abel KM, McNamee R, Pedersen MG, Webb RT, Baker PN, Kenny LC, Mortensen PB (2008) Higher risk of offspring schizophrenia following antenatal mater- nal exposure to severe adverse life events. Arch Gen Psychiatry 65: 146–152
  • 12. Time Table of Normal Foetal Brain Development 15 Kostovic I, Jovanov-Milosevic N (2006) The development of cerebral connections during the first 20–45 weeks’ gestation. Semin Fetal Neonatal Med 11: 415–422 Lagercrantz H, Hanson M, Evrard P, Rodeck C (2002) The Newborn Brain. Neuroscience and clinical applications. Cambridge University Press, Cambridge, UK Linderkamp O (2005) Gehirnentwicklung bei Feten und Fr¨uhgeborenen, in: Fr¨uhgeborene optimal ern¨ahren und pflegen, Frank C, Linderkamp O, Pohlandt F, pp. 126–131. Kirch- heim, Mainz Linderkamp O, Janus L, Linder R, Skoruppa D (2009a) Development of the foetal brain. Genetics and experience-driven plasticity. Int J Prenat Perinat Psychol Med (in press) Linderkamp O, Janus L, Linder R, Skoruppa D (2009b) Effects of prenatal stress on brain development. Int J Prenat Perinat Psychol Med (in press) Lopez B, Schwartz SJ, Prado G, Campo AE, Pantin H (2008) Adolescent neurological development and its implications for adolescent substance use prevention. J Prim Prev 29: 5–35 Lossi L, Merighi A (2003) In vivo cellular and molecular mechanisms of neuronal apoptosis in the mammalian CNS. Prog Neurobiol 69: 287–312 Maffei A, Nataraj K, Nelson SB, Turrigiano GG (2006) Potentiation of cortical inhibition by visual deprivation. Nature 443: 81–84 Miller JH, McKinstry RC, Philip JV, Mukherjee P, Neil JJ (2003) Diffusion-tensor MR imaging of normal brain maturation: a guide to structural development and myelina- tion. Am J Roentgenol 180: 851–859 Mo Z, Moore AR, Filipovic R, Ogawa Y, Kazuhiro I, Antic SD, Zecevic N (2007) Human cortical neurons originate from radial glia and neuron-restricted progenitors. J Neurosci 27: 4132–4145 Naves G, Cooke SF, Bliss TV (2008) Synaptic plasticity, memory and the hippocampus: a neural network approach to causality. Nat Rev Neurosci 9: 65–75 Nicolic M, Reynolds R (2008) Mechanisms governing neuronal migration and morphology. Dev Neurosci 30: 1–222 Perkins L, Hughes E, Srinivasan L, Allsop J, Glover A, Kumar S, Fisk N, Rutherford M (2008) Exploring cortical subplate evolution using magnetic resonance imaging of the fetal brain. Dev Neurosci 30: 211–220 Petanjek Z, Judas M, Kostovic I, Uylings HB (2008) Lifespan alterations of basal dendritic trees of pyramidal neurons in the human prefrontal cortex: a layer-specific pattern. Cereb Cortex 18: 915–929 Plomin R, Spinath FM (2004) Intelligence: Genetics, genes, and genomics. J Personal Soc Psychol 86: 112–129 Rakic P (2003) Developmental and evolutionary adaptations of cortical radial glia. Cereb Cortex 13: 541–549 Ridgway R, House SH (2006) The Unborn Child. Beginning a Whole Life and Overcoming Problems of Early Origin. Karnac, London, UK Ridley M (2003) Nature via Nurture. Genes, Experience and What Makes us Human. Harper Collins, London Rutter M (2006) Genes and Behavior: Nature-Nurture Interplay Explained. Blackwell, Cambridge, MA Saxena S, Caroni P (2007) Mechanisms of axon degeneration: from development to disease. Prog Neurobiol 83: 174–191 Turkewitz G (2007) The relevance of the fetal and neonatal period for the development of novelty preferences, learning, habituation and hemispheric specialization. Dev Psy- chobiol 49: 780–787
  • 13. 16 Otwin Linderkamp et al. Uylings HB, Malofeeva LI, Bogolepova IN, Jacobsen AM, Amunts K, Zilles K (2005) No postnatal doubling of number of neurons in human Broca’s areas (Brodmann areas 44 and 45)? A stereological study. Neuroscience 136: 715–728 Van den Bergh BR, Van Calster B, Smits T, Van Huffel S, Lagae L (2008) Antenatal mater- nal anxiety is related to HPA-axis dysregulation and self-reported depressive symptoms in adolescence: A prospective study on the fetal origins of depressed mood. Neuropsy- chopharmacology 33: 536–545 Volpe JJ (2008) Neurology of the Newborn, 5th ed. Saunders Co., Philadelphia Waites CL, Craig AM, Garner CC (2005) Mechanisms of vertebrate synaptogenesis. Annu Rev Neurosci 28: 251–274 Zhang CL, Zou Y, He W, Gage FH, Evans RM (2008) sA role for adult TLX positive neural stem cells in learning and behaviour. Nature 451: 1004–1007 Correspondence to: Otwin Linderkamp, Prof. Dr., Kornmarkt 3, 69117 Heidelberg, Ger- many, E-Mail olinderkamp@yahoo.de