Disrupting somatosensory processing impairs motor execution but not motor imagery


While motor imagery (MI) is thought to be 'functionally equivalent' with motor execution (ME), the equivalence of feedforward/back mechanisms between the two modalities is unexplored. Here, we tested the equivalence of these mechanisms between MI and ME via two experiments designed to probe the role of somatosensory processing (Exp 1), and cognitive processing (Exp 2). All participants engaged in a force-matching task adapted for MI. A reference force was applied (1-10) to one index finger while participants matched the force with their opposite index finger via ME or MI (control conditions). Participants then rated the force (1-10). Exp 1: Participants (N = 27) additionally performed the task with tactile stimulation (ME+TAC, MI+TAC). Exp 2: Participants (N = 15) performed the task in dual-task conditions (ME+COG, MI+COG). Pearson's correlations were computed to test the association between reference forces and force ratings in each condition. Within each practice modality, effect sizes were calculated on resultant correlation coefficients between control and experimental conditions (e.g., MI minus MI+TAC). Results indicate that (Exp 1) tactile stimulation impaired performance in ME (d = 0.46) but not MI (d = -0.02). Dual-task conditions (Exp 2) impaired performance to a greater extent in MI (d = 0.70) than ME (d = -0.49). The dissociable pattern of results suggests while somatosensory processing is critical for ME, it is not for MI. In contrast, MI may rely on cognitive resources not required by ME. Overall, findings indicate a functional equivalence between feedforward mechanisms in MI and ME may not exist.

Acknowledgments: This work was supported by internal UBC funding (ASPIRE) awarded to SK.