HUMAN MOTOR MEMORY RETENTION REQUIRES FRONTO-PARIETAL CIRCUIT PLASTICITY

Previous work has documented the involvement in motor learning and retention of a region in the posterior postcentral gyrus, overlying brain areas 2 and 5, which we refer to here as the rostral parietal cortex. This area is neuroanatomically connected to dorsal premotor cortex and accordingly learning related changes to this region of parietal cortex may be associated with corresponding changes to the dorsal premotor zone. To test this hypothesis, adaptation to altered visual feedback was used as an experimental model. Following learning, continuous theta burst magnetic stimulation (cTBS) was applied to either primary motor cortex, to the rostral parietal cortex, or to dorsal premotor, to test for their contribution to learning. In retention tests, 24h later, disruption of rostral parietal cortex or dorsal premotor cortex each led to an impairment, whereas disruption of primary motor cortex did not. When rostral parietal cortex and dorsal premotor cortex were both disrupted together, to test for independent effects on retention, the impairment was no greater than if either area alone was disrupted. This indicates that these areas are interconnected in a motor learning circuit such that disruption of either one results in a similar impairment when the circuit is broken. In addition, this work shows there is adaptation and learning in humans which does not depend on primary motor cortex.