The Roles of Primary Motor and Dorsal Premotor Cortex in Motor Adaptation

摘要

The brain has a remarkable ability to rapidly adapt behavior. On the scale of development, the brain learns to control the complex dynamics of our limbs by forming and pruning synaptic connections. However, the motor system also learns on much shorter timescales, such as when learning to hit the bullseye of a dartboard, or using a new tool. This process, referred to as motor learning, may be mediated by interactions between the cerebellum and areas of the cerebral cortex including primary motor (M1) and dorsal premotor cortex (PMd). PMd is involved in movement planning with strong connectivity with M1, the main cortical output to the spinal cord. Both are intimately interconnected with the cerebellum. Although cortical reorganization is believed to underlie the long-term learning of motor skills, it is unlikely to account for the rapid adaptation that is observed experimentally. In this project, I studied how behavioral adaptation arises from the coordinated activity of neural populations in the motor cortex. I recorded from neurons in both M1 and PMd as monkeys learned to compensate for perturbations applied to their reaching movements. I show that throughout learning neurons in M1 maintain a fixed relationship with the dynamics of movement, suggesting that adaptation may not involve cortical reorganization. Instead, behavioral changes are mediated through the altered recruitment of M1 neurons. I then study the population-level activity patterns of M1 and PMd and show that PMd plays a direct role in learning how to control the dynamics of the limb by modifying the motor plans sent to M1, potentially by interactions with the cerebellum. These modified plans are executed without changing the functional interactions between neurons in either area, or from PMd to M1. These results provide new insight into the process of motor adaptation and the neural control of movement, and highlight a population-wide mechanism that could help to explain rapid learning processes through the brain.