Abstract
Because compensatory changes in brain activity underlie functional recovery after brain damage, monitoring of these changes will help to improve rehabilitation effectiveness. Functional near-infrared spectroscopy (fNIRS) has the potential to measure brain activity in freely moving subjects. We recently established a macaque model of internal capsule infarcts and an fNIRS system for use in the monkey brain. Here, we used these systems to study motor recovery in two macaques, for which focal infarcts of different sizes were induced in the posterior limb of the internal capsule. Immediately after the injection, flaccid paralysis was observed in the hand contralateral to the injected hemisphere. Thereafter, dexterous hand movements gradually recovered over months. After movement recovery, task-evoked hemodynamic responses increased in the ventral premotor cortex (PMv). The response in the PMv of the infarcted (i.e., ipsilesional) hemisphere increased in the monkey that had received less damage. In contrast, the PMv of the non-infarcted (contralesional) hemisphere was recruited in the monkey with more damage. A pharmacological inactivation experiment with muscimol suggested the involvement of these areas in dexterous hand movements during recovery. These results indicate that fNIRS can be used to evaluate brain activity changes crucial for functional recovery after brain damage.
Highlights
Because compensatory changes in brain activity underlie functional recovery after brain damage, monitoring of these changes will help to improve rehabilitation effectiveness
Neuronal motor systems have the capacity for functional recovery following brain damage such as that induced by stroke, and functional recovery can be enhanced by postlesion rehabilitative training[1,2]
This result is consistent with our previous study using positron emission tomography (PET) scans in macaque monkeys, which showed that the PMv is involved in the recovery of hand movements after lesioning of M121
Summary
Because compensatory changes in brain activity underlie functional recovery after brain damage, monitoring of these changes will help to improve rehabilitation effectiveness. Enhanced involvement of the PMv was observed with functional magnetic resonance imaging (fMRI) of stroke patients during recovery of hand movements[12,14], indicating that this area is a candidate for assessing the effectiveness of rehabilitative training for hand motor dysfunction after brain damage. In a previous study[25], we developed an fNIRS system for monitoring macaque cerebral motor activity during voluntary movements without head fixation We recently used this system to successfully monitor functional hemodynamic responses in motor-related cortical areas reproducibly over long periods of time. We used this system to investigate whether brain activity changes during functional recovery after brain damage could be evaluated by fNIRS
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