Developmental neuroplasticity
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The document discusses developmental neuroplasticity in the visual cortex. It describes how thalamic input first establishes basic mapping in the cortex during early development. During the critical period, visual experience can alter circuit structure and function. Neurons in the primary visual cortex develop orientation and direction selectivity. Early abnormal visual experience can lead to lasting impairment, while normal experience is important for maturation. Neurotrophins released with coordinated neural activity strengthen synapses during development and recovery.
Developmental neuroplasticity
- 2. Cortical columns functions: •AMPLIFICATION •COMPUTATION •COMMUNICATION HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 3. Visual cortex development Thalamic input is recieved first in the cortical layer 4 (stellate cells). Precritical fase of the development: establishment of basic mapping function that allows the thalamus to map into layer 4 of the cortex. Critical fase is when the visual experience can alter the structure and the function of the circuits. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 4. Primary visual cortex and topographic map Topographic map: fovea is encoded in the most posterior parts of the primary visual cortex, perhipheral parts of the retina are encoded in the more anterior parts of the visual cortex. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 5. Ocular dominance Two eyes project to separate layers of cells within the lateral geniculate nucleus. The contralateral eye projects to layers 1, 4 and 6. The ipsilateral eye projects to layers 2, 3 and 5. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 6. Layer 5 Layer 4 Layer 3 Layer 6 Layer 2 Layer 1 Parvocellular layers project to layer C4β of the visual cortex and those cells and axons are concerned with shape and color of objects. Magnocellular layers project to layer C4 of the visual cortex and those cells and axons are concerned with motion of objects. Koniocellular layers synapse in the zones rich with oxidative metabolism in the layer 3 of the visual cortex.Their function is unknown. Contralateral eye projections Ipsilateral eye projections
- 7. Critical period • In the early postnatal life neuronal circuits are sensitive to changes in activity dependent modulation of ongoing neural activity by sensory experience. • Cortical blindness will persist if the onset of eye deprivation was in the early postnatal life. • If there is correctible eye disorder, it should be treated early in life to prevent life long visual impairment. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 8. Orientation selectivity and preference Visual cortex neurons are specialised to specifically oriented visual receptive field. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 9. Direction selectivity and preference Visual cortex neurons are also specialised to specifically directed visual receptive field. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 10. Receptive fields in retina and thalamus Receptive fields in visual cortex And so on...
- 11. Pinwhell centers Pinwheel centers in the visual cortex contain the cortical columns that represent all possible orientations for a given set of overlapping receptive fields. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 12. Pinwhell centers HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY PINWHEEL
- 13. Key factors of neuronal self-organisation • Neuronal circuits are dynamical systems: activity dependent plasticity. • Neuronal circuits grow long ranging axonal connections that are able to bind together the activity of different cortical columns with similar preferences. • Visual cortex self organises into pinwheel formations with π density. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 14. Bad vs. NO experience Bad experience (abnormal vision) is worse (more detrimental to the development of visual cortical circuits) than NO experience (lack of experience). HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 15. Conclusions for orientation preference of receptive fields in visual cortex • Normally, self-organization operates synergistically with sensorimotor experience to promote full functional maturation. • When there is abnormal experience, synergy is broken and the neuronal circuits are functionally impaired. • Neuronal circuits that underlie orientation columns, self organise to adapt to the quality of the incoming sensory signals. • Neuronal circuits are harmed by abnormal experience. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 16. Conclusions for direction preference of receptive fields in visual cortex The neuronal circuits that underlie direction columns can not self-organize. They must be instructed (trained) by visual experience with moving stimuli. The window of opportunity for the motion training is very brief: early experience is critical. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 17. Final concluding marks • Normal sensorimotor experience has a profound effect on the formation and maturation of neural circuits in the cerebral cortex. • Some properties (timing-based properties like direction selectivity) may not develop without normal experience in the early critical period. • Abnormal sensorimotor experience in early critical period may lead to lasting functional impairment. • Normal experience in early life is critical! HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 18. Neurotrophins and developmental neuroplasticity II. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 19. Hebb´s postulate Coordinated activity of a presynaptic terminal and a postsynaptic cell will strengthen that synaptic connection. Uncoordinated activity of a presynaptic terminal and a postsynaptic cell will weaken that synaptic connection. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 20. Neurotrophins • The production and release of neurotrophins is activity dependent. • Interconnected and coordinated neurons will strengthen their interconnections (synapses) and will be nourished via the release and retrograde activity of neurotrophins in presynaptic neurons. • Circuits driven by abnormal experience (connected neurons, but not functionally coordinated) will weaken their interconnections (synapses): insufficient neurotrophic support. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 21. Neurotrophins In maturity the regulated secretion of trophic factors may help shape neuronal connections in response to injury or adaptation to new patterns of neural activity. In recovering brain BDNF (brain derived neurotrophic factor) activity has been linked to adaptive circuit plasticity. Variations in BDNF gene render cortical circuits more or less adaptive to challenges in motor learning and cognition. HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY
- 22. Literature https://www.coursera.org/learn/medical- neuroscience: Leonard E. White, PhD, Duke University HTTPS://WWW.COURSERA.ORG/LEARN/MEDICAL-NEUROSCIENCE: LEONARD E. WHITE, PHD, DUKE UNIVERSITY