Functional localization of the supplementary motor area

Abstract

The supplementary motor area (SMA) is a key structure involved in behavioral planning and execution. Although many reports have indicated that SMA is organized somatotopically, its exact organization remains still unclear. This study aimed to functionally map SMA using functional magnetic resonance imaging (fMRI) and validate the fMRI-SMA by electrocortical stimulation (ECS) and postsurgical symptoms. Total 32 healthy volunteers and 24 patients participated in this study. Motor tasks were right and left finger tapping and language tasks included simple reading, lexical decision for presented words, and verb generating tasks. SPM8 was used to conduct individual and group analyses. In all subjects, the lexical decision task induced the greatest number of active fMRI pixels in SMA. fMRI during the language tasks showed anterior part of SMA compared to finger tapping tasks. We found an overlap spot with all different tasks in posterior part of SMA, which we termed SMA core. Six patients underwent awake craniotomy for ECS mapping for primary regions and SMA. During awake craniotomy, ECS to posterior part of SMA, which might involve the possible SMA core consistently, evoked both speech arrest and flaccid hemiparesis. The SMA mapping suggested posterior part of SMA might play more important roles in any executions, which might involve the SMA core.