1. Developmental neuroplasticity
Domina Petric, MD

2. Cortical columns functions:
AMPLIFICATION
COMPUTATION
COMMUNICATION
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.
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.
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.
Leonard E. White, PhD, Duke University

6. 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

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.
Leonard E. White, PhD, Duke University

8. Orientation selectivity and preference
Visual cortex neurons are specialised to specifically oriented visual receptive field.
Leonard E. White, PhD, Duke University

9. Direction selectivity and preference
Visual cortex neurons are also specialised to specifically directed visual receptive field.
Leonard E. White, PhD, Duke University

10. Receptive fields in visual cortex
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.
Leonard E. White, PhD, Duke University

12. Pinwhell centers
PINWHEEL
Leonard E. White, PhD, Duke University

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.
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).
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.
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.
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!
Leonard E. White, PhD, Duke University

18. Neurotrophins and developmental neuroplasticity
II.
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.
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.
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.
Leonard E. White, PhD, Duke University

22. Literature
Leonard E. White, PhD, Duke University
Leonard E. White, PhD, Duke University