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Functional near-infrared spectroscopy (fNIRS) is suitable for measuring brain functions during neurorehabilitation
because of its portability and less motion restriction. However, it is not known whether neural reconstruction can be
observed through changes in cerebral hemodynamics. In this study, we modified an fNIRS system for measuring the
motor function of awake monkeys to study cerebral hemodynamics during neurorehabilitation. Computer simulation was
performed to determine the optimal fNIRS source–detector interval for monkey motor cortex. Accurate digital phantoms
were constructed based on anatomical magnetic resonance images. Light propagation based on the diffusion equation
was numerically calculated using the finite element method. The source–detector pair was placed on the scalp above the
primary motor cortex. Four different interval values (10, 15, 20, 25 mm) were examined. The results showed that the
detected intensity decreased and the partial optical path length in gray matter increased with an increase in the source-detector
interval. We found that 15 mm is the optimal interval for the fNIRS measurement of monkey motor cortex. The
preliminary measurement was performed on a healthy female macaque monkey using fNIRS equipment and custom-made
optodes and optode holder. The optodes were attached above bilateral primary motor cortices. Under the awaking
condition, 10 to 20 trials of alternated single-sided hand movements for several seconds with intervals of 10 to 30 s were
performed. Increases and decreases in oxy- and deoxyhemoglobin concentration were observed in a localized area in the
hemisphere contralateral to the moved forelimb.
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