The effects of explicit and implicit information on modulation of corticospinal excitability during hand-object interactions

Abstract

During skilled hand-object interactions, the human sensorimotor system generates predictive motor commands based on visual information and sensorimotor memories established from previous experience. Here we investigated whether predictive force scaling could be adapted to context-dependent information that is not always explicitly available. We probed the effect of motor prediction mechanisms on corticospinal excitability (CSE) with transcranial magnetic stimulation (TMS). In experiment 1, participants performed a continuous force tracking task by squeezing a manipulandum. We varied the type of visual information for predicting motor output by displaying either the actual target force curve participants had to match (sinusoidal curve condition) or the visual error between the required and exerted force (horizontal line condition). CSE was modulated by the rate of change of forces (speed) in both conditions. Force direction changes further modulated CSE but in the sinusoidal curve condition only. These findings indicate that the corticospinal output mainly reflects the ongoing motor command, but can also be modulated by less explicit contextual information. In experiment 2, we tested whether participants could accurately predict the required force scaling in a standard random weight object lifting task, which also included series of small weight increments. Results showed that participants were unable to generate accurate force predictions by extrapolating weight from the implicit series, which failed to modulate CSE, unsurprisingly. Altogether, these findings suggest that corticospinal output is modulated based on context-dependent information when mediated by explicit visual cues, but not when sensorimotor cues are presented in an implicit manner.HighlightsVisual cues and sensorimotor experience are key for hand-object interactionsWe investigated the underlying corticospinal excitability (CSE) changesVisual cues improved motor performance and modulated CSECSE was partly modulated by less explicit informationImplicit information did not improve motor performance and nor modulate CSE