Tuesday, October 26, 2010

Did neural reuse play a role in language evolution?

There's an interesting article in the new of the Behavioral and Brain Sciences along with a number of equally interesting commentaries:

An emerging class of theories concerning the functional structure of the brain takes the reuse of neural circuitry for various cognitive purposes to be a central organizational principle. According to these theories, it is quite common for neural circuits established for one purpose to be exapted (exploited, recycled, redeployed) during evolution or normal development, and be put to different uses, often without losing their original functions. Neural reuse theories thus differ from the usual understanding of the role of neural plasticity (which is, after all, a kind of reuse) in brain organization along the following lines: According to neural reuse, circuits can continue to acquire new uses after an initial or original function is established; the acquisition of new uses need not involve unusual circumstances such as injury or loss of established function; and the acquisition of a new use need not involve (much) local change to circuit structure (e.g., it might involve only the establishment of functional connections to new neural partners). Thus, neural reuse theories offer a distinct perspective on several topics of general interest, such as: the evolution and development of the brain, including (for instance) the evolutionary-developmental pathway supporting primate tool use and human language [-my emphasis, M.P.]; the degree of modularity in brain organization; the degree of localization of cognitive function; and the cortical parcellation problem and the prospects (and proper methods to employ) for function to structure mapping. The idea also has some practical implications in the areas of rehabilitative medicine and machine interface design.
I think stressing the importance of things like neural reuse and recruitment also fits in nicely with a recent post over at Replicated Typo about the role of "Domain-General Regions and Domain-Specific Networks" in the evolution of language, where Wintz proposes a rough outline of a possible evolutionary scenario for the emergence of language:
  1. Relaxed selection allowed developmental processes to open up new levels of functional complexity;
  2. This functional complexity was achieved through allowing additional neural systems to influence a specific type of behaviour;
  3. With these new possibilities now unmasked, natural selection then operated on maintaining this functional complexity by preparing individuals for linguistic input;
  4. One suggestion for how this might be achieved is through selection for neural circuitry that aids in creating the networks that subserve language processing;
  5. So instead of having domain-specific modules, humans have domain-general modules that are networked in a domain-specific manner.
  6. Rapidly acquired, and seemingly ubiquitous, features across languages are therefore more likely to have been the product of cultural evolutionary processes that enable a language to adapt to various constraints, including: domain-general mechanisms, the transmission vector, demography, the environment etc.

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