Optical imaging of motor cortical hemodynamic response to directional arm movements using near-infrared spectroscopy

This study aims at determining arm-movement directions from functional near-infrared spectroscopy (fNIRS) hemodynamic signals in order to decode intentional motor commands, originating in the motor cortices of humans, which could be implemented in neuroprosthetic assistive devices for assisting th e physically disabled. Motor cortical hemodynamic responses were recorded using 64 spatially distributed optrodes from 14 normal subjects during free arm orthogonal movements in the x- and y-directions on a horizontal plane. The time course of oxy-(HbO2) and deoxy-hemoglobin (Hb), and of their summation (HbO2 + Hb) and difference (HbO2 – Hb) signals, representing the hemodynamic profiles of total oxygen delivery and ext raction, respectively, were computed for the localized neuronal populations in the motor cort ices underlying the optrodes. Analysis of the above hemodynamic signals revealed that they could be temporally, spatially, or spatiotemporally decoupled, depending on the movement d irection. Thus, by analyzing the spatiotemporal profiles of brain activation we could identify the direction of the orthogonal movements uniquely. Our findings demonstrate that movement direction, a key feature of motor commands, can be reliably extracted in real-time from surface recorded fNIRS signals, and support their viability in future noninvasive assistive devices.