Brain Specialization Specialization and Integration

The brain adheres to two fundamental principles of organization, functional integration and functional specialization. The integration among specialized cortical areas depends upon cortico-(sub)cortical connections and the neuronal interactions they mediate. The characterization of functional specialization is important in many areas of neuroscience and provides an infrastructure within which normal brain function can be understood (e.g., cognitive neuroscience) and how things might go wrong (e.g., neuropsychology and clinical neuroscience). The distinction between specialization and integration relates to the distinction between localizationism and (dis)connectionism that dominated thinking about brain function in the nineteenth century. Since the early anatomic theories of Gall, the identification of a particular brain region with a specific function has become a central theme in neuroscience. However, functional localization per se was not easy to demonstrate: for example, a meeting entitled "Localization of Function in the Cortex Cerebri" in 1881 addressed the difficulties of attributing function to a cortical area, given the dependence of cerebral activity on underlying connections (Phillips, Zeki, & Barlow, 1984). Goltz (1881), although accepting the results of electrical stimulation in dog and monkey cortex, considered the excitation method inconclusive in that the movements elicited might have originated in related pathways or current could have spread to distant areas. In short, the excitation method could not be used to infer functional localization because localizationism discounted interactions among areas. It was concluded that lesion studies should supplement excitation experiments. Ironically, it was observations on patients with brain lesions (Absher & Benson, 1993) some years later that led to the concept of disconnection syndromes and the refutation of localiza-tionism as a sufficient account of cortical organization.

Functional localization implies that a function is localized in an area, whereas specialization suggests that a cortical area is specialized for some aspects of cognitive, perceptual, or sensorimotor processing. The cortical infrastructure supporting a single function may involve many specialized areas whose union is mediated by functional integration. In this view functional specialization is only meaningful in the context of functional integration and vice versa.

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