The Interactions Between Primary Somatosensory and Motor Cortex during Human Grasping Behaviors

Afferent inputs to the primary somatosensory cortex (S1) are differentially processed during precision and power grip in humans. However, it remains unclear how S1 interacts with the primary motor cortex (M1) dur -ing these two grasping behaviors. To address this question, we measured short-latency afferent inhibition (SAI), reflecting S1-M1 interactions via thalamo-cortical pathways, using paired-pulse transcranial magnetic stimulation (TMS) during precision and power grip. The TMS coil over the hand representation of M1 was oriented in the posterior-anterior (PA) and anterior-posterior (AP) direction to activate distinct sets of corticospinal neurons. We found that SAI increased during precision compared with power grip when AP, but not PA, currents were applied. Notably, SAI tested in the AP direction were similar during two-digit than five-digit precision grip. The M1 receives movement information from S1 through direct cortico-cortical pathways, so intra-hemispheric S1 -M1 interactions using dual-site TMS were also evaluated. Stimulation of S1 attenuated M1 excitability (S1-M1 inhi-bition) during precision and power grip, while the S1-M1 inhibition ratio remained similar across tasks. Taken together, our findings suggest that distinct neural mechanisms for S1-M1 interactions mediate precision and power grip, presumably by modulating neural activity along thalamo-cortical pathways. (c) 2021 IBRO. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the interactions between the primary somatosensory cortex (S1) and the primary motor cortex (M1) during precision and power grip. The results indicate that S1-M1 interactions differ between precision and power grip, with increased short-latency afferent inhibition (SAI) observed during precision grip. Additionally, the study reveals that S1-M1 interactions mediate precision and power grip by modulating neural activity along thalamo-cortical pathways.