Brain and Its Functions- Part 3

Brain and Its Functions Part 3 Dr. Prithika Chary Consultant Neurologist and Neurosurgeon Adopted by Prof.K.Prabhakar, [email_address]

Can We change Brain? Many a times we are under the mistaken notion that brain goes through an irreversible process. Once it is formed we cannot change it. In reality the latest research show that Brain is Plastic. You can change your brain physiology by constant learning. Therefore I am a sixty year old man, I cannot change my profession or learn new skills is not correct. In fact a person at any given point of a time in his life time subjected to having healthy organs can CHANGE HIS Or HER BRAIN.

Neuroplasticity Is the lifelong ability of the brain to reorganize neural pathways based on new experiences

Can the brain change ? Is it nature or nurture? Twenty years ago we thought that the structure of the brain develops during childhood and once that organization in the brain has been developed that there is very little room for changes and for plastic alterations. Now we know that there is enormous capacity. In addition to genetic factors, the brain is shaped by the characteristics of a person's environment and by the actions of that same person.

PLASTIC – Ability to adapt Brain plasticity means the ability of the nervous system to adapt to changed circumstances, to find new ways of learning, sometimes after an injury or a stroke, but more commonly when you want to acquire a skill for, say, a hobby or even a new job. The ability of the brain to change with learning is what is known as neuroplasticity .

NEUROPLASTICITY Involves many processes Involves changes occurring throughout one’s life Involves all parts of the nervous system, neurons, glia and vascular cells Is of four different types as we know it today

NEUROPLASTICITY Neuroplasticity does not consist of a single type of morphological change, but rather includes several different processes that occur throughout an individual’s lifetime. Many types of brain cells are involved in neuroplasticity, including neurons, glia, and vascular cells.

Periods of rapid change or plasticity occur in the brain under four main conditions: Developmental plasticity : when the immature brain first begins to process sensory information Activity-dependent plasticity : when changes in the body, like a problem with eyesight, alter the balance of sensory activity received by the brain Plasticity of learning and memory : when we alter our behavior based on new sensory information Injury-induced plasticity : following damage to the brain

While plasticity occurs over an individual’s lifetime, different types of plasticity dominate during certain periods of one’s life and are less prevalent during other periods . During normal brain development when the immature brain first begins to process sensory information through adulthood (developmental plasticity and plasticity of learning and memory). As an adaptive mechanism to compensate for lost function and/or to maximize remaining functions in the event of brain injury.

What are the basic processes involved in brain development? Neurogenesis is the formation of neurons in the brain Neural migration is the movement of neurons to different areas of the brain Myelination, the covering of the neuron's axon with a fatty sheath, allows neurons to conduct signals more efficiently and protects the axon Synaptogenesis is the formation of synapses, or connections between neurons Synaptic Pruning is the selective elimination of synapses

Developmental Plasticity: Synaptic Pruning Over the first few years of life, the brain grows rapidly. As each neuron matures, it sends out multiple branches (axons, which send information out, and dendrites, which take in information), increasing the number of synaptic contacts and laying the specific connections from neuron to neuron. At birth, each neuron in the cerebral cortex has approximately 2,500 synapses.

Developmental Plasticity: Synaptic Pruning By the time an infant is two or three years old, the number of synapses is approximately 15,000 synapses per neuron (Gopnick, et al., 1999). This amount is about twice that of the average adult brain. As we age, old connections are deleted through a process called synaptic pruning .

ACTIVITY DETERMINED NEUROPLASTICITY Synaptic pruning eliminates weaker synaptic contacts while stronger connections are kept and strengthened. Experience determines which connections will be strengthened and which will be pruned; Connections that have been activated most frequently are preserved. Neurons must have a purpose to survive. Without a purpose, neurons die through a process called apoptosis in which neurons that do not receive or transmit information become damaged and die.

APOPTOSIS Apoptosis is called “ programmed cell death “ It takes place to avoid redundancy in the nervous system For the right cells to die/or less cells to die nurturing the child’s brain is necessary with adequate stimulation, because neurons that have nothing to do will just literally kill themselves

APOPTOSIS The illustration shows a neuron undergoing a common form of apoptosis. (A) The healthy neuron has a defined cell membrane and the cytoplasm and nucleus, which contains DNA, are intact. (B) When apoptosis kicks in, the cell contorts and the DNA breaks up. (C) In the final stage of apoptosis, the cell is broken into membrane-bound pieces. Specialized cells called macrophages or microglia remove the debris

Cortical Maps The cortex contains maps These maps represent our skills and our knowledge of the world. And the brain's mapmakers are kept very busy, indeed. When a skill develops or changes, the cortical maps also change, and neuron populations may be annexed for specific purposes, later abandoned, and sometimes annexed again.

The adult brain is driven by behavioral experience We now know that the brain is plastic: it can and does remodel itself, sometimes within a remarkably short period of time. These biological changes in the adult brain aren't driven by developmental timelines or inherited traits. Instead, they are driven by behavioral experience Just as the migratory behavior of residents can change the map of a city, so can our learning behavior change the maps in our brain, causing neurons populations to synchronize their actions, respond to new inputs, and support new skills.

Practice makes perfect When we approach learning seriously, however, something else happens: we attend to a task, we practice it over and over again, and we become emotionally involved. Under these conditions, brain plasticity happens - the winemaker can sharpen her taste buds, the blind person can learn to read Braille, the musician can perfect his pitch, and you can become an honest-to-goodness guitar player.

Selective attention Why are attention, repetition, and intensive practice the prerequisites of brain plasticity? Do we really have to listen to our teachers, go to class every day, and do homework every night? In 1890, philosopher and psychologist William James wrote. My experience is what I agree to attend to. Only those items which I notice shape my mind - without selective interest, experience is an utter chaos."

space and time The crucial role played by the dimensions of space and time doesn't end with our behavioral experience. Brain maps change spatially by taking over neighboring neuronal populations on different parts of the cortex. But brain maps can also change in time , by synchronizing the actions of neurons more tightly so that a specific group of neurons may provide near-simultaneous responses to the same input.

Versatility These timing relationships may actually help support the plasticity of existing cortical maps and the generation of new ones, because a single neuron can participate in the representation of several different sensory or motor representations at different times.

Keeping in touch If we take a closer look at a single neuron and its synaptic connections, we see that timing is everything. Suppose a neuron sends weak, sporadic chemical messages to the another neuron. This situation is a bit like receiving postcards once every few years from a long-lost acquaintance - the messages aren't always effective enough to cause a sustained reaction in the second neuron

Weightlifting for the Mind: Enriched Environments and Cortical Plasticity In the 1960's in Berkeley's biology labs, Mark Rosenzweig and his colleagues Edward Bennett, Marian Diamond, and David Krech made a proposition -- that experience can induce concrete and observable changes in brain structure – This would profoundly influence our understanding of education and the human mind for decades afterwards.

If negative early experiences could impair brain development, could positive experiences enhance the brain? At Harvard, David Hubel and Torsten Wiesel studied cats raised blind in one eye, and by 1962 they had demonstrated that such deprivation caused profound structural changes in the cats' visual cortex. This work made it clear that severe deprivation during critical developmental periods could have catastrophic effects on a growing brain , but the question of whether the opposite was true remained.

"cerebral exercise" Rats raised in an "enriched" environment, with toys and social activities, were not only smarter than rats raised in impoverished environments, but that the improvement in performance correlated with an increase in the weight of the rats' cerebral cortex. The idea that the brain, like a muscle, might respond to "cerebral exercise" with physical growth was surprising to many , and gave strength to an increasingly powerful theory suggesting that all aspects of the mind - from memory, to dreams, to emotions - might have physical correlates.

Enriched Environments The brain expects, and perhaps even depends upon, interaction with the environment in order to develop and reach maturation. Babbling may assist in the development of language capabilities, just as playing with objects assists in development of motor skills.

Enriched Environments Children who are exposed to a rich and varied education early in life develop a great capacity for learning throughout life. Real learning, not just rote exercise, can have a dramatic influence on the physical structure of the brain.

The orange dots represent the multiple synapses on a single neuron. The extent of synaptic interconnectivity as we age determines our functional ability to use our brains In spite of losing neurons as we age, the densitiy of interconnectivity makes up for the loss This depends on continuous new learning & environmental enrichment USE IT OR LOSE IT

Developmental Plasticity – synaptic pruning Ineffective or weak connections are "pruned" in much the same way a gardener would prune a tree or bush, giving the plant the desired shape. It is plasticity that enables the process of developing and pruning connections, allowing the brain to adapt itself to its environment.

Plasticity of Learning and Memory It was once believed that as we aged, the brain’s networks became fixed. In the past two decades, however, an enormous amount of research has revealed that the brain never stops changing and adjusting. Learning, as defined by Tortora and Grabowski (1996), is “the ability to acquire new knowledge or skills through instruction or experience. Memory is the process by which that knowledge is retained over time.

LEARNING The capacity of the brain to change with learning is plasticity. So how does the brain change with learning? According to Durbach (2000), there appear to be at least two types of modifications that occur in the brain with learning: A change in the internal structure of the neurons , the most notable being in the area of synapses. An increase in the number of synapses between neurons.

Learning Windows During a child's development, there are a series of time periods, or "windows," in which a child can best learn or refine a particular ability, such as speech. After this time period is over it becomes much more difficult, sometimes impossible, for the child to learn the same thing.

Myelination There are millions of neurons, which form the electrical connections that let us think. These cells send their signals through axons, some of which can reach a length of up to a meter in humans. Wrapped around many of the axons are cells which form myelin sheaths, composed mainly of fat. These sheaths serve to insulate the axon, letting its signal travel about 100 times faster than in an unmyelinated axon.

Myelination Myelinization is the key to learning windows Myelination is the major cause of the increase in a child's brain size. At birth, the infant brain weighs 300-350 grams (2/3 to ¾ pound). In the first four years of life, the brain increases to 80% of the adult weight of 1200-1500 grams (2.6 - 3.3 pounds).

At birth… Few nerve centers are myelinated at birth. In the beginning, only reflexes needed for survival are completely myelinated However, after birth the primary visual and auditory cortex neurons rapidly receive their myelination.

In childhood… Myelination continues. During the first year-and-a-half of life, the corticospinal motor tract receives its myelination enabling gross control over arms, torso, and legs. The brain continues to change and mature during adolescence

During Adolescence… Final myelination of the frontal lobes occurs in early adolescence. An adolescent's brain reaches the weight of an adult brain by about age fourteen due to myelin accumulation and dendritic branching. At this time the potential for contribution to insight, judgment, inhibition, reasoning, and social conscience are possible.

During Adolescence… The adolescent's frontal lobes are increasingly active, and this ability enables the adolescent to consider several things in the mind while comparing or interrelating them. The density of synapses declines during adolescence due to selective pruning of redundant or unused connections. Synapse formation continues despite ongoing pruning

Into Adulthood… The brain continuously remodels itself-even into adulthood. Synapses continue to be formed in select areas of the brain but growth of new neurons is limited Lifelong enrichment experiences are important

Injury-induced Plasticity: Plasticity and Brain Repair During brain repair following injury, plastic changes are geared towards maximizing function in spite of the damaged brain. In studies involving rats in which one area of the brain was damaged, brain cells surrounding the damaged area underwent changes in their function and shape that allowed them to take on the functions of the damaged cells. Although this phenomenon has not been widely studied in humans, data indicate that similar (though less effective) changes occur in human brains following injury.

Plasticity after amputation When nerve stimulation changes, as with amputation, the brain reorganizes. In one theory, signals from a finger and thumb of an uninjured person travel independantly to separate regions in the brain's thalamus (left). After amputation, however, neurons that formerly responded to signals from the finger respond to signals from the thumb (right).

Babies start to babble around six to ten months of age, and that not long afterward they say a few words like "no" or "uh-oh.“ At around two years, already more like children and less like babies, they begin speaking grammatically correct sentences and their vocabulary undergoes a growth spurt. And by three years, most children can speak in a manner that is essentially adult-like. LANGUAGE ACQUISITION

LANGUAGE ACQUISITION Research has identified certain areas of the adult brain that are typically responsible for specific aspects of language, and these can serve as starting points for understanding children's brains. The left hemisphere appears to be critical in most right handers and many left handers Lesions to the right hemisphere are not usually associated with language loss, but there is evidence that the right hemisphere plays a role in emotion The right hemisphere has the potential to assume some language functions if the left hemisphere is damaged .

BRAIN LATERALIZATION The term brain lateralization refers to the fact that the two halves of the human brain are not exactly alike. Each hemisphere has functional specializations : some function whose neural mechanisms are localized primarily in one half of the brain.

WHAT DOES HANDEDNESS HAVE TO DO WITH BRAIN LATERALIZATION? Most humans (70% to 95%)(but not all) have left hemisphere specialization for language abilities. 5% to 30% have anomalous patterns of specialization. These might include: (a) having a right-hemisphere language specialization or (b) having little lateralized specialization.

Thank you and go to Part 4 You will understand the application of Brain and its Functions in the context of Management disciplines.

Brain and Its Functions- Part 3

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Brain and Its Functions- Part 3