Deconvolution of transcranial magnetic stimulation (TMS) maps

Transcranial magnetic stimulation (TMS) is a noninvasive method for local s timulation of cerebral cortex using a small coil's pulsed magnetic field. T MS response maps consist of measured responses to stimulations at points on a scalp-referenced grid and are used to study the topography of the brain' s inhibitory and excitatory response. Because the magnetic field distributi ons of stimulation coils are 1-2 centimeters wide and 2-3 centimeters long, and the induced electric fields are even broader, the resolution of TMS ma ps is limited and the actual region of cortical stimulation is poorly defin ed. To better characterize the activation pattern, a practical mathematical procedure was developed for deconvolving a spherical model approximation o f the coil's induced electric held distribution (here measured in a phantom ) from the TMS response maps. This procedure offers an integrated, internal ly consistent method for processing TMS response maps to estimate the spati al distribution of motor cortex activations and inhibitions.