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The evolutionary emergence of the mammalian neocortex is generally accepted as the key neural innovation underlying advanced reason. Cortical evolution, if the neural constructivists are correct, is not simply A story about the addition of new, special purpose brain structures. Rather, it is A story about the addition of A plastic resource geared to allowing the encountered environment to build dedicated, delicately fitted neural substructures “on-the-hoof.” The human neocortex and prefrontal cortex, along with the extended developmental period of human childhood, allows the contemporary environment an opportunity to partially redesign aspects of our basic neural hardware itself. The designer environments are thus matched, step-by-step, by dedicated designer brains, with each side of the co-adaptive equation growing, chaining, and evolving to better fit- and maximally exploit- the other. It is in this way that the human learner becomes “dovetailed” to the set of a reliable external problem- solving resources that she encounters during early learning.
The neural constructivist vision thus depicts neural and especially cortical growth as experience-dependent and involving the actual construction of new neural circuitry (synapses, axons, dendrites) rather than just the fine-tuning of circuitry whose basic shape and function is already determined. The learning device itself changes as A result of an organism- environmental interactions; learning does not just alter the knowledge base for the fixed computational engine, it alters the internal computational architecture itself.
A concrete example, consider the development of hearing. Congenitally deaf children, whose brains are thus never exposed to the complex and distinctly structured inputs that the auditory world provides, fail to develop the complex web of inner connectivity that supports normal hearing. If such stimulation is artificially provided, using a cochlear implant, recovery is rapid. The neural bases of this recovery are increasingly well understood and involve complex changes in the connectivity and response characteristics of the auditory cortex. Vision cortex, likewise, requires extensive, experience-dependent rewriting to support seeing. Newborn human infants have a very bad vision; it is highly restricted in scope and the resolution is forty times worse than adult vision. Depth appreciation is pretty well nonexistent. It takes about A year of “cortical training” for the visual system to become normal, A process that can be blocked by cataracts or other impairments, which deprive the visual cortex of the experience it needs. Remove cataracts and replace the affected lens with A clear artificial one, and improvement is again dramatically fast. According to one researcher, this kind of result “demonstrates the amazing plasticity of the young brain and underscores the importance of complex, balanced, early sensory input for guiding subsequent brain development.
So, great in fact is the plasticity of the immature cortex (and especially that of the prefrontal cortex, according to Quartz and Sejnowski) that O’Leary dubs it “Protocortex”. The whole sensory, linguistic, and technological environment in which the human brain grows and develops is thus poised to function as one of the anchor points around which such flexible neural resources adapt and fit. Such neural plasticity is, of course, not restricted to the human species; in factor, some of the early work on cortical transplants was performed on rats. But our brains do appear to be far and away from the most plastic of them all. Combined with this plasticity, however, we benefit from A unique kind of developmental space; the unusually protracted human childhood.
In A recent evolutionary account, Griffiths and Stotz argue that the long human childhood provides A unique of opportunity in which “cultural scaffolding [can] change the dynamics of the cognitive system in A way that opens up new cognitive possibilities. “ These authors argue against what they describe as the “dualist account of human biology and human culture” according to which biological evolution must first create the “anatomically modern human” before being followed by the long and ongoing process of Cultural Revolution. Such A picture, they suggest, invites us to believe in something like A basic biological human nature, gradually co-opted and obscured by the trappings and effects of culture and society. This vision (which is perhaps not so far removed from that found in some of the more excessive versions of evolutionary psychology) is akin, they argue to looking for true nature of the ant by “removing the distorting influence of the nest”.