Wearable fNIRS device of higher spatial resolution realized by triangular arrangement of dual-purpose optodes

The human cerebral cortex is composed of gyri of approximately 10–15 mm in width that have independent functions. To explore their activities with functional near-infrared spectroscopy (fNIRS), hemodynamic responses at single gyri should be measured. Most fNIRS devices only offer a channel arrangement with a larger interval size than the gyrus width, which can cause false negative errors in detecting cortical activation localized within 10–15 mm, and this has been an obstacle using fNIRS to explore cortical activities. Previously, we demonstrated doubling of the channel density using a triangular arrangement of dual-purpose optodes with a minimum number of optodes that was almost equivalent to that used in conventional arrangements. To implement this method as a wearable device for human measurement, we developed a dual-purpose optode to function both as the source and detector with the base unit triangularly mounted by three optodes, and the connectors joining plural base units with three-way joints. Optodes in this triangular arrangement illuminated and detected in sequence between adjacent optodes and performed high-density 15-mm measurements in channel intervals. Measurements of 30 channels on an adult human successfully detected hemodynamic responses to unilateral finger movements at the motor-related cortical regions according to their functions.