The Causal Interactions Between Bilateral M1 and SMA During Verb Comprehension, Motor Imagery and Hand Motion

Abstract

Background: The role of the sensory-motor system in semantic representation has caused increasing research interest. Although previous studies have shown different activations in the motor system during action verb processing, motor imagery and action execution, whether motor system interaction is modulated by task demand is still unknown. Objectives: To address the issue, the current study used effective connectivity analysis to investigate how task demand influences causal interactions among bilateral supplementary motor areas (SMA) and primary motor cortex (M1). Materials and Methods: Nineteen participants performed a verb reading task, a motor imagery task, and a hand motion task in an fMRI experiment, and their brain activity related to task performances was examined. Granger causality analysis was used to compute causal interactions among activity in the bilateral M1 and bilateral SMA in three tasks. Results: Granger causality analysis indicated that the hand motion task elicited the most complicated network and that the passive reading task elicited the fewest connections among the four areas. Furthermore, only the passive reading task elicited left lateralized connectivity between M1 and SMA. In addition, motor imagery and hand motion execution elicited negative influences from the right SMA to other areas. Conclusions: These results together suggest that although the motor network involved in action verb processing shared some interactions with those in motor imagery and hand motion execution, semantic representation during language comprehension is different from the raw sensory-motor experiences supported by the primary cortical areas.