Functional magnetic resonance imaging and transcranial magnetic stimulation

Abstract

Functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) represent different approaches to mapping the motor cortex. fMRI identifies areas of hemodynamic changes during task performance while TMS provides electrophysiologic data concerning the localization and density of cortical motoneurons. Here we define the spatial correlation between fMRI and TMS maps and compared them with direct electrical cortical stimulation (ECS). We performed fMRI at 1.5 T on 3 normal subjects and 2 patients with mass lesions near the central sulcus using a multislice, asymmetric, spin-echo, echo-planar pulse sequence during the performance of a motor task. We also performed focal TMS with surface EMG recordings from the muscles primarily involved in the fMRI task. We coregistered the stimulation sites in real time with the fMRI maps using a frameless stereotactic system. In both patients we also performed ECS of the cortex during surgery under local anesthesia. fMRI maps were validated by the electrophysiologic data both pre- and intraoperatively. Our results suggest that regions of fMRI activation correspond spatially to areas of highest motoneuron density as demonstrated by electrophysiologic techniques.