Neural Connectivity and Neuropsychological Function

Excerpt

A tradition in neuropsychology has been to devise tests that are sensitive and selective to lesions in specific brain structures. The structures supporting the functions have been implicitly understood to be gray matter—neurons, nuclei—the seat of function. One-to-one, brain-to-behavior relations between a neuronal locus and a single function were the gold standard of early neuropsychologists and founded on “pure” cases with circumscribed, single lesions. This view of brain-behavior relations proved to be essential for initial attempts to establish neural substrates of cognitive, sensory, and motor functions and for convincing the scientific and medical communities of the functional selectivity of brain sites. Despite the importance of these neuro/psychological concepts, they ultimately have proved to be unrealistically narrow to account for many, if not most, patterns of functional impairments. In the majority of individuals who sustain brain insult, the damage is commonly multi-focal, whether from dementing disorders, closed head injury, or even focal hippocampal epilepsy, a concomitant being bilateral extrahippocampal tissue volume deficits. The observations and insights of Norman Geschwind laid the groundwork for breaking set from the purists’ accounts of brain structure-function relations and for providing a brain-based framework for interpreting impairments resulting from multi-focal lesions. …