Brain development - Neural proliferation

6 important questions on Brain development - Neural proliferation

Nearly all neurons are produced prenatally, except for

  • Dentate gyrus of the hippocampus
  • olfactory bulb

Passive cell displacement

  • Older cells are pushed up by recently born cells
  • outside-in pattern = more mature cells in outer layers and younger cells are inside (e.g. Thalamus, hippocampus)

Active cell migration

  • Young cells moving past previously pattern generated cells
  • inside-out pattern = more mature layers are inside whilst younger outside (e.g. Laminar structure of the cerebral cortex)
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Most adults have similar functions within approximately the same areas of the cortex, but how is it possible?
2 hypothesis

  • Protomap hypothesis
  • Protocortex hypothesis

Theory:
despite primary sensory regions being the best candidates for genetic pre-specification, these regions can have their properties significantly changed through experience.
Conclusion:

Sensory input may be vital at least for the maintenance of cortical divisions

Current reviews of the evidence converge on views that are midway between the protomap and protcortex hypotheses:

  • Graded patterns of gene expression create large-scale regions with combinations of properties that may better suit certain computations (similar to a very coarse protomap)
  • it is within these large-scale regions that smaller scale functional areas arise through the activity-dependent mechanisms associated with the protocortex view

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