Large-scale cortical reorganization in the premotor-parietal connections of a macaque model with primary motor cortical lesion and recovery

Neuromotor systems can functionally recover after local damage, but changes in the underlying cortical network remain unclear. In a nonhuman primate model of primary motor cortex (M1) lesions and motor recovery, we previously reported reorganization of subcortical output projections from the ipsilesional ventral premotor cortex (ip-PMv) to the cerebellum. In this study, we investigated the rewiring of cortico-cortical connections between the ip-PMv and parietal cortex using the same model. We injected biotinylated dextran amine (BDA) into the ip-PMv and compared the BDA labeling in the areas around the intraparietal sulcus between an M1-lesion/recovery group and an intact group. The M1-lesion/recovery group had fewer BDA-labeled boutons and cell bodies in the ipsilesional anterior intraparietal area (ip-AIP) than the intact group, suggesting a reciprocal decrease in the PMv-AIP network involved in motor programs for grasping, with an indirect impact of M1 lesions at the network level. There was also a decrease in BDA-labeled boutons in the contralesional AIP, indicating interhemispheric changes. Conversely, the M1-lesion/recovery group had more BDA-labeled boutons in the posterior part of the ventral intraparietal area in the ipsilesional hemisphere (ip-VIP), potentially indicating a compensatory increase in parietal networks. Some of the projections from the ip-PMv to the ip-VIP neurons were confirmed to be functional because the synaptic markers colocalized with BDA-labeled boutons. These findings show that the adult primate brain can reorganize large-scale cortical networks and achieve functional recovery following motor lesions, which has implications for understanding the neural mechanisms underlying motor recovery and for developing rehabilitation strategies.