DISTINCTIVE ELECTROPHYSIOLOGICAL CHARACTERISTICS OF FUNCTIONALLY DISCRETE BRAIN-AREAS - A TENABLE APPROACH TO FUNCTIONAL LOCALIZATION

The direct cortical response (DCR), an electrical potential recorded i n the immediate vicinity of a surface cortical stimulus, shows a confi guration in the primary sensory areas of animals that is different fro m the one observed in association cortex. This suggested the possibili ty that systematic study of the DCR in the human brain might reveal a profile of configurations in which the form of the response provides f unctional information about the gyri being tested. Studies were carrie d out in subhuman primates and in patients undergoing surgery for tumo rs, occult vascular malformations, and epilepsy. In the animals, DCR's from somatosensory, motor, and association cortex are distinguishable ; however, there are no differences in configuration between motor and premotor responses, or between association responses from prefrontal and parietal cortex. In patients with epilepsy due to nonspace-occupyi ng pathology, the responses did not show distinguishing features. In c ontrast, in the patients with tumors or occult vascular malformations, DCR's from somatosensory, motor, and premotor cortex could be readily distinguished from each other. Responses along the mid and posterior sylvian fissure of the dominant hemisphere also had distinctive featur es, but more data are needed before the significance of this finding w ith respect to language function can be assessed. The accumulating res ults suggest that analysis of DCR's may prove to be a useful method fo r functional localization in individuals with focal space-taking patho logy.