Distinctive electrophysiological characteristics of functionally discrete brain areas: a tenable approach to functional localization.

The direct cortical response (DCR), an electrical potential recorded in the immediate vicinity of a surface cortical stimulus, shows a configuration in the primary sensory areas of animals that is different from the one observed in association cortex. This suggested the possibility that systematic study of the DCR in the human brain might reveal a profile of configurations in which the form of the response provides functional information about the gyri being tested. Studies were carried out in subhuman primates and in patients undergoing surgery for tumors, 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-occupying pathology, the responses did not show distinguishing features. In contrast, 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 features, but more data are needed before the significance of this finding with respect to language function can be assessed. The accumulating results suggest that analysis of DCR's may prove to be a useful method for functional localization in individuals with focal space-taking pathology.