Adaptive modifications of cortical activity patterns during motor learning

As part of the ongoing effort to design a close-loop robust neuroprosthesis, this study investigated adaptive changes in the spike activity of cerebral cortical neurons during motor adaptation. Chronic multielectrode recordings was performed from small populations of neurons in the primary motor (M1), dorsal premotor (PMd) and part of parietal (area 5) cortical areas of rhesus monkeys during the animals' performance of a 3D reaching task and adaptation to predictable external force perturbation. The obtained data allowed us to analyze the adaptation-related day-to-day modifications in the spike activity of the neuronal ensemble. A significant portion of sampled neurons became more task-related during the adaptation process. The main feature of the adaptation observed in M1 was the buildup of spike activity preceding the perturbation onset. The resulting pattern was retained for at least two days after the perturbations had been discontinued, but the buildup significantly decreased after the perturbations became randomly scattered across trials. Neurons in PMd increased activity intensity in response to the "go" signal as anticipation for impending perturbation as adaptation progressed. A gradual attenuation of the response to the perturbation onset was observed in area 5. The response quickly reappeared after the perturbations became random, suggesting that the attenuation was related to the anticipation of a perturbation. The results are consistent with viewing the cerebral cortex as a pool of functionally flexible processing units that can be dynamically incorporated into a system controlling the performance of a given motor task and adjusted as required for motor learning.