Spike-timing-dependent plasticity in primate corticospinal connections induced during free behavior.

Abstract

Motor learning and functional recovery from brain damage involve changes in the strength of synapticconnections between neurons. Relevant invivo evidence on the underlying cellular mechanisms remains limited and indirect. We found that the strength of neural connections between motor cortex and spinal cord in monkeys can be modified with an autonomous recurrent neural interface that delivers electrical stimuli in the spinal cord triggered by action potentials of corticospinal cells during free behavior. The activity-dependent stimulation modified the strength of the terminal connections of single corticomotoneuronal cells, consistent with a bidirectional spike-timing-dependent plasticity rule previously derived from invitro experiments. For some cells, the changes lasted for days after the end of conditioning, but most effects eventually reverted to preconditioning levels. These results provide direct evidence of corticospinal synaptic plasticity invivo at the level of single neurons induced by normal firing patterns during free behavior.