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State-dependent motor associative plasticity relies on parietal activity during action planning

Poster Session B - Sunday, March 8, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballroom

Taylor Finkelstein¹ (taylorfi@umich.edu), Francesco Mirabelli², Taraz Lee¹, Ambra Bisio², James Brissenden¹, Stephan Taylor¹, Thad Polk¹, George Wittenberg³, Michael Vesia¹; ¹University of Michigan, ²University of Genoa, ³University of Pittsburgh

Frontal motor and parietal regions are highly interconnected and play a critical role in goal-directed motor behavior. Some suggest that parietal activity during the planning of goal-directed actions, such as object grasping, influences stimulation-induced distal motor plasticity, but it has been difficult to provide strong causal evidence for this claim in humans. Here, we examined how activity in the posterior parietal cortex (PPC) influences state-dependent associative plasticity in the parietal-motor circuit. Using a within-subject design, participants completed three stimulation conditions during right-hand object-directed grasping, a task that reliably engages PPC activity during action planning. Continuous theta-burst stimulation (cTBS) was applied to the left PPC or a left visual cortex control site to transiently disrupt neural activity, followed by a Hebbian plasticity induction protocol in the left parietal-motor circuit using cortico-cortical paired associative stimulation (cPAS). To determine whether PPC suppression alone modulates motor cortical plasticity, a third condition combined cTBS to the left PPC with a non-Hebbian plasticity cPAS protocol with altered interregional timing. Plasticity was assessed by measuring changes in motor-evoked potentials (MEPs) elicited with single-pulse transcranial magnetic stimulation before and after each protocol. cTBS to the PPC significantly reduced the task-engaged, state-dependent cPAS-induced increase in MEP amplitudes, whereas active cTBS to the visual cortex had no effect. cTBS to the PPC, followed by a non-Hebbian cPAS protocol, produced no change in MEP amplitudes from baseline. These findings provide strong causal evidence that parietal activity during action planning regulates the induction of state-dependent parietal-motor plasticity necessary for dexterous hand function.

Topic Area: PERCEPTION & ACTION: Motor control