Interareal connectivity in the human language system: a cortico-cortical evoked potential study

Abstract

Objective To investigate functional connectivity in the human language system in vivo by means of a cortico-cortical evoked potential (CCEP) study. Methods Eight epilepsy patients underwent chronic subdural electrode implantation in the language dominant hemisphere for epilepsy surgery. Single pulse electrical stimuli were delivered to the anterior language (eight patients), posterior language (four) or face motor (two) area, and CCEPs were obtained by averaging electrocorticograms recorded from the perisylvian and extrasylvian basal temporal language areas time locked to the stimulus. Results Stimulation at the anterior language area elicited CCEPs (7/8 patients at 3–21 electrodes) in the middle and posterior part of the superior temporal gyrus, the adjacent part of the middle temporal gyrus and the supramarginal gyrus. CCEPs occurred at and/or around the core language area identified by conventional electrical stimulation. Similar early and late CCEPs were obtained from the basal temporal area by stimulating the anterior language area (3/3). In contrast, stimulation of the adjacent face motor area did not elicit CCEPs in language areas but rather in the postcentral gyrus. Stimulation of the posterior language area produced CCEPs in the anterior language (3/4) as well as in the basal temporal area (1/2). Conclusion This study, for the first time, demonstrated that perisylvian and extrasylvian language areas participate in the language system as components of a network by means of feed-forward and feed-back projections. Judging from the CCEP distribution in the posterior language area, a rather broad neuronal network seems to surround the previously recognized core region of this area.