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Developing children are in a critical period during which they are much better at learning certain tasks like speaking a language. After the critical period ends, children have a qualitatively more difficult time learning these tasks.

What specific changes in a child's brain are responsible for the drastic difference in learning during and after the critical period? Are these changes just to the plasticity and rate of neuorogenesis?

Notes

  • The best understood critical period is phoneme recognition and production; I am fine with answers that are specialized to this task.
  • It is important to explain how the neurobiological changes produce a change in learning that seems so qualitatively different and sudden compared to the gradual decreases in learning at other times.

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Here's an article which includes a study on cats that found some interesting brain changes in cats in the end of their critical period: asha.org/Publications/leader/2009/090414/f090414b It's under the second heading, "What happens at the end of the sensitive period, if little or no auditory stimulation is provided to the brain?" –  Ben Brocka Feb 14 '12 at 14:07
    
@BenBrocka thanks, a quick skim suggests that Klinke, R., Hartmann, R., Heid, S., Tillein, J., & Kral, A. (2001) (or any of the results by Kral and co-authors for that matter) is probably a better source for understanding the details. I don't have time to read that right now, but having a result from cats would be a good (maybe partial) answer. –  Artem Kaznatcheev Feb 14 '12 at 14:11
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I don't have journal access so I wasn't able to check those out (unless someone is hosting them for free). I know it's not exactly what you asked about but there's lots of research into cochlear implants on the critical period and what changes are caused. Lots of the results are still relevant RE brain changes even if they're trying to find something CI related. –  Ben Brocka Feb 14 '12 at 15:00
    
A related TEDx talk by Patricia Kuhl. –  Artem Kaznatcheev Oct 17 '12 at 17:41
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1 Answer 1

The truth is, we don't fully know. There are likely a number of factors. One of them seems to be the Brain Derived Neurotrophic Factor (BDNF). This molecule seems to be involved with maintaining and encouraging neuron growth. In Rats with a transgenically accelerated rise in BDNF levels, the critical period began earlier, and finished earlier as well (Huang et al., 1999). This doesn't exactly get at the heart of the question, because clearly there is some interaction between experience and expression of this gene. It's a good starting point, however.

References

Huang, Z.J., Kirkwood, A., Pizzorusso, T., Porciatti, V., Morales, B., Bear, M.F., Maffei, L., & Tonegawa, S. (1999) "BDNF Regulates the Maturation of Inhibition and the Critical Period of Plasticity in Mouse Visual Cortex", Cell 98(6): 739-755. doi:10.1016/S0092-8674(00)81509-3

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