Organization of the mouse motor cortex studied by retrograde tracing and intracortical microstimulation (ICMS) mapping.

The motor representation of the body musculature was studied in 11 adult mice by using ICMS. The motor responses elicited from both granular and agranular cortical fields showed that the mouse motor cortex is topographically organized; however, within the representation of individual body-parts the movements are multiply represented. In addition, several sites were encountered where more than one movement was elicited at the same stimulus threshold. The locations of pyramidal cells contributing axons to the pyramidal tract were examined by means of retrograde tracing with HRP injected into the cervical enlargement. This procedure labeled neurons only in lamina V in granular and agranular cortical fields. The similarities between the organization of motor cortex demonstrated in this study and the organization in the rat suggest that the rat and mouse share a common plan of rodent motor cortical organization.