A method for analysis of electrophysiological responses obtained from the motor fibers of the human internal capsule

Abstract

During stereotactic surgery in the ventrolateral (VL) thalamic nucleus we localized the motor fibers of the internal capsule (IC) by electrophysiological stimulation. Knowledge of the location and motor somatotopy in the IC helps predict the boundaries of the VL. Although the somatotopy of the IC in individual patients is determined during their respective surgeries, quantitative analysis of somatotopic data from multiple subjects within a common magnetic resonance imaging (MRI) reference space has not been attempted. Here we describe a method for group analysis, in a single coordinate system, of responses obtained from the IC adjacent to the thalamus. We analyzed tongue, face, arm, and leg motor responses in 25 cases of thalamotomy. We used existing software to develop a three dimensional (3D) database of motor responses. Our preliminary analysis suggests a face-anterior to leg-posterior somototopic organization, with some overlap between adjacent representations.