Modulation of grip force in unimanual manipulation tasks after theta burst stimulation over the dorsal premotor cortex

Abstract

Aiming to examine the role of dorsal premotor cortex (PMd) during fine coordination of fingertip forces we applied theta burst repetitive magnetic stimulation (TBS) to disrupt neural processing in that specific area, after which subjects were performed various static and dynamic manipulation tasks (ramp-and-hold, oscillation force producing and simple lifting tasks) that recorded the grip (G) and load force (L) performed unimanual. In the two experiments nine healthy subjects (27.2 ± 4.1 yrs) used an instrumented device that recorded the grip and load force before and after we applied continous TBS (cTBS) either sham stimulation over contralateral PMd. There were no changes for static manipulation tasks in both stimulation protocols. After cTBS applied over dominant hemisphere grip force was disrupted only for simple lifting task. Our subjects have shown consistent differences of G/L ratio pre (1.10 ± 0.21) and post cTBS procedure (0.95 ± 0.23; p = 0.019). Our results suggest that inhibitory TBS protocol applied over PMd modulates the function of skillful and precise finger movements during object lifting. These findings support the role of PMd in human motor control and forces generation required to hold small objects stable in our hands.