Developmental neuroplasticity Domina Petric, MD

Cortical columns functions: AMPLIFICATION COMPUTATION COMMUNICATION https://www.coursera.org/learn/medical-neuroscience: Leonard E. White, PhD, Duke University

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

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

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

Ipsilateral eye projections Layer 6 Parvocellular layers project to layer C4β of the visual cortex and those cells and axons are concerned with shape and color of objects. Layer 5 Layer 4 Layer 3 Magnocellular layers project to layer C4 of the visual cortex and those cells and axons are concerned with motion of objects. Layer 2 Layer 1 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

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

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

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

Receptive fields in visual cortex Receptive fields in retina and thalamus Receptive fields in visual cortex And so on...

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

Pinwhell centers PINWHEEL https://www.coursera.org/learn/medical-neuroscience: Leonard E. White, PhD, Duke University

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

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

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

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

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

Neurotrophins and developmental neuroplasticity II. https://www.coursera.org/learn/medical-neuroscience: Leonard E. White, PhD, Duke University

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

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

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

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