Motor Learning Selectively Strengthens Cortical and Striatal Synapses of Motor Engram Neurons

Learning and consolidation of new motor skills require adaptations of neuronal activity and connectivity in the motor cortex and striatum, two key motor regions of the brain. Yet, how neurons undergo synaptic changes and become recruited during motor learning to form a memory engram remains an open question. Here, we train mice on a single-pellet reaching motor learning task and use a genetic approach to identify and manipulate behavior-relevant neurons selectively in the primary motor cortex (M1). We find that the degree of reactivation of M1 engram neurons correlates strongly with motor performance. We further demonstrate that learning-induced dendritic spine reorganization specifically occurs in these M1 engram neurons. In addition, we find that motor learning leads to an increase in the number and strength of outputs from M1 engram neurons onto striatal spiny projection neurons (SPNs) and that these synapses form local clusters along SPN dendrites. These results identify a highly specific synaptic plasticity during the formation of long-lasting motor memory traces in the corticostriatal circuit.