Functional near-infrared spectroscopy reveals functional rewiring between macaque motor areas following post-infarction recovery of manual dexterity

Post-stroke motor recovery relies on the functional reorganization of motor-related cortical areas to compensate for damaged neural circuitry related to motor functions. Functional near-infrared spectroscopy (fNIRS) offers a promising method for monitoring cortical reorganization during rehabilitation, although its feasibility has not yet been fully established. We developed a high-density fNIRS system for measuring cortical activity in macaques and validated its effectiveness in assessing changes in directed functional connectivity among motor cortical areas in response to functional recovery from brain damage. Data were previously collected from two female Japanese macaque monkeys ( Macaca fuscata ) before focal infarcts occurred in the posterior limb of the internal capsule and following the confirmed recovery of hand movements through rehabilitation training. In the present study, time-varying conditional Granger causality during either unaffected- or affected-hand movement was evaluated among several motor areas, and the changes resulting from functional impairment and subsequent recovery were analyzed. Changes in channel-level directed functional connectivity around the ventral premotor areas were examined in detail for their relevance to motor recovery. The analysis revealed network changes involving multiple motor-related cortical regions. In the monkey with a small infarct, connectivity changes primarily occurred within the ipsilesional hemisphere, whereas in the monkey with a larger infarct, both contralesional and interhemispheric connectivity change was observed. These results align with the findings obtained from high spatial resolution brain measurements in patients and animal models following brain damage. They suggest that functional connectivity analysis using fNIRS is effective for monitoring the brain’s functional changes underlying motor recovery. Significance Statement We analyzed brain activity in macaque monkeys both before the induction of focal infarcts in the internal capsule and after the recovery of hand movements, using functional near-infrared spectroscopy (fNIRS). Directed functional connectivity among motor-related cortical areas during hand movement tasks was assessed using time-varying conditional Granger causality. The results revealed task-dependent directed functional connectivity among several motor areas, indicating network changes (functional rewiring) involving multiple regions. Notably, a small infarct primarily affected connectivity within the ipsilesional hemisphere, whereas a larger infarct involved both contralesional and interhemispheric connections. The results of the present study suggest that task-dependent functional connectivity changes measured by fNIRS can be used to assess cortical reorganization associated with post-stroke motor recovery.