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We have developed a brain-machine interface (BMI) by using a method based on near-infrared spectroscopy. We call our interface "Optical-BMI". It functions as a practical, unrestrictive, non-invasive brain-switch without the need for large equipment. During an experiment with the prototype system, an operator manipulated external electrically controlled equipment while we measured the corresponding spatiotemporal changes in the hemoglobin concentration in the blood flowing through his or her pre-frontal cortex by using a probe cap with 22 measurement points.

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Optical topography (OT) based on near infrared spectroscopy (NIRS) is useful for measuring changes in the concentrations of oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) in brain tissues non-invasively. Conventional OT systems limit subjects' ranges of movement to within the length of optical fibers these systems require for irradiating light on the scalp and detecting light transmitted through the tissues in the human head. We developed a prototype of a multi-channel, portable OT system without optical fibers. We used the portable system to measure changes in the concentrations of oxy-Hb and deoxy-Hb in the frontal cortex while the subjects performed a word fluency task. The results show typical changes in hemoglobin concentrations during the task and suggest the prototype system can be used to investigate brain functions in the frontal cortex.

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