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:
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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