Skilled motor training causes the cortical representation of the trained body parts to expand into regions of the motor cortex related to other body parts. However, the effect of neuroplastic changes on the neurons originally existing within the expanded area is not well understood. In this study, the extent of the neuroplastic changes after achieving sufficient motor learning and the impact of the expansion on the neurons related to movements of other body parts were investigated. Rats were trained to perform a single-pellet retrieval reaching task, and intracortical microstimulation in the motor cortex was used to assess neuroplastic changes. After 54 to 73 days of training, the trained rats achieved sufficient motor learning. In the motor cortex, the occurrence rate of evoked wrist movements increased to approximately double that of the control group in the expanded area. This finding suggests that the extent of neuroplastic changes in the occurrence rate of evoked movements in the motor cortex achieved through sufficient motor learning is approximately double. Additionally, stimulation in the expanded area predominantly evoked vibrissae movements in the control group
however, the occurrence rate and threshold of evoked vibrissae movements were not significantly changed in the expanded areas in the trained group. This observation may suggest that the expansion of cortical areas corresponding to the trained body parts does not disrupt the original function of movements of other parts in the expanded area.