Differences of Intracranial Electrical Stimulation Thresholds in the Human Brain.

Abstract

The thresholds of current intensities required to evoke a clinical response during intracranial electrical stimulation mapping vary. We wanted to test if there is systematic variation of threshold currents between different brain areas. Electrode contacts of depth electrodes in a series of patients undergoing presurgical evaluation for epilepsy surgery were stimulated. The brain regions we studied included the insular cortex, the pericentral cortex, and the intervening white matter. Current intensities that elicited clinical responses in central subcortical white matter tracts were significantly lower than those needed to evoke a clinical response in the cortex. We found systematic differences of threshold stimulation intensities between cortical and subcortical structures in the human brain. In addition to known neurophysiologic differences between white and grey matter, the systematic difference in stimulation thresholds may be due to the direction of the white matter tracts with respect to the electrode orientation and to inherent properties of specific brain regions.