Cortical Correlates of Learning in Monkeys Adapting to a New Dynamical Environment

We are recording from monkeys as they execute delayed, visually instructed reaching movements. In our experiments, monkeys learn to adapt to a new dynamic perturbation, namely a force field. By comparing the activity in the movements before and after the adaptation, we can dissociate the kinematics and the dynamics of the movements. Furthermore, we can dissociate the neuronal activity leading to the movement from the effects of the adaptation. Using this paradigm, we have previously studied the movement-related activity of neurons in M1, the primary motor cortex. We found that neurons exhibit a learning-dependent plasticity. As the monkeys learn the new force field, the neurons change their activation patterns, and they keep the new activation once the perturbation is removed.

With respect to the movement-related activity, we found similar results in the supplementary motor area (SMA). Compared to M1, SMA has a much more pronounced activity during the instructed delay preceding the movement. Analyzing this activity, we find that the dynamics of the movement is already reflected during the delay (that is during motor planning). Furthermore, neurons show a progressive kinematics-to-dynamics transformation during the delay. The extent to which this transformation occurs anti-correlates with the following reaction time and correlates with how "well-adapted" is the actual movement. Future work includes a study of the effects of reversible lesions of SMA in the force field adaptation task.