Dissociating the causal role of left and right dorsal premotor cortices in planning and executing bimanual movements – A neuro-navigated rTMS study

BACKGROUNDThe dorsal premotor cortex (PMd) is a key region in bimanual coordination. However, causal evidence linking PMd functionality during motor planning and execution to movement quality is lacking.OBJECTIVEWe investigated how left (PMdL) and right PMd (PMdR) are causally involved in planning and executing bimanual movements, using short-train repetitive transcranial magnetic stimulation (rTMS). Additionally, we explored to what extent the observed rTMS-induced modulation of performance could be explained by rTMS-induced modulation of PMd-M1 interhemispheric interactions (IHI).METHODSTwenty healthy adults (mean age ± SD = 22.85±3.73 years) participated in two sessions, in which either PMdL or PMdR was targeted with rTMS (10Hz) in a pseudo-randomized design. PMd functionality was transiently modulated during the planning or execution of a complex bimanual task, whereby the participant was asked to track a moving dot by controlling two dials. The effect of rTMS on several performance measures was investigated. Concurrently, rTMS-induced modulation of PMd-M1 IHI was measured using a dual-coil paradigm, and associated with the rTMS-induced performance modulation.RESULTSrTMS over PMdL during planning increased bilateral hand movement speed (p=0.03), thereby improving movement accuracy (p=0.02). In contrast, rTMS over PMdR during both planning and execution induced deterioration of movement stability (p=0.04). rTMS-induced modulation of PMd-M1 IHI during planning did not predict rTMS-induced performance modulation.CONCLUSION(S)The current findings support the growing evidence on PMdL dominance during motor planning, as PMdL was crucially involved in planning the speed of each hand, subserving bimanual coordination accuracy. Moreover, the current results suggest that PMdR fulfills a role in continuous adjustment processes of movement.