A wearable multi-channel fNIRS system for brain imaging in freely moving subjects

Abstract

Functional near infrared spectroscopy (fNIRS) is a versatile neuroimaging tool with an increasing acceptance in the neuroimaging community. While often lauded for its portability, most of the fNIRS setups employed in neuroscientific research still impose usage in a laboratory environment. We present a wearable, multi-channel fNIRS imaging system for functional brain imaging in unrestrained settings. The system operates without optical fiber bundles, using eight dual wavelength light emitting diodes and eight electro-optical sensors, which can be placed freely on the subject's head for direct illumination and detection. Its performance is tested on N = 8 subjects in a motor execution paradigm performed under three different exercising conditions: (i) during outdoor bicycle riding, (ii) while pedaling on a stationary training bicycle, and (iii) sitting still on the training bicycle. Following left hand gripping, we observe a significant decrease in the deoxyhemoglobin concentration over the contralateral motor cortex in all three conditions. A significant task-related ΔHbO2 increase was seen for the non-pedaling condition. Although the gross movements involved in pedaling and steering a bike induced more motion artifacts than carrying out the same task while sitting still, we found no significant differences in the shape or amplitude of the HbR time courses for outdoor or indoor cycling and sitting still. We demonstrate the general feasibility of using wearable multi-channel NIRS during strenuous exercise in natural, unrestrained settings and discuss the origins and effects of data artifacts. We provide quantitative guidelines for taking condition-dependent signal quality into account to allow the comparison of data across various levels of physical exercise. To the best of our knowledge, this is the first demonstration of functional NIRS brain imaging during an outdoor activity in a real life situation in humans.

Using Fiberless, Wearable fNIRS to Monitor Brain Activity in Real-world Cognitive Tasks

“…Given the need to bring functional imaging instruments outside the lab and given recent technological improvements, portable and wearable electroencephalography (EEG) and functional near infrared spectroscopy (fNIRS) systems have been developed [6][7][8][9][10][11] . One of the major advantages of fNIRS over EEG is its higher spatial resolution.…”

“…The first fiberless systems were equipped only with a small number of channels (e.g., single channel 15 and 2 channels 16 ) limiting the investigation to small areas. More recently, multichannel wireless and wearable fNIRS devices have been developed 6,7,[17][18][19][20] giving the possibility to monitor larger portions of the head on freely moving participants.…”

Hemispheric differences in electrical and hemodynamic responses during hemifield visual stimulation with graded contrasts

“…Finally, the block-averaged hemodynamic responses were calculated. A typical cerebral activation is characterized by a significant increase in HbO concentration or a significant decrease in HbR concentration with respect to the baseline after the activation onset [38]. The spatial distribution maps of the groupaveraged hemodynamic responses were calculated based on the maximum values of the group-averaged hemodynamic responses from 5 seconds after the stimulation onset until the end of the stimulation.…”

“…Moreover, the rate of increase in the HbO concentration was greater than the rate of decrease in the HbR concentration. This may be due to a relatively higher signal-to-noise ratio for HbO, which can improve its robustness to cross-talk [38]. For a given stimulus, the changes in the hemodynamic response are produced by a series of complex processes, including the neuronal activity responding to the stimulus, the neurovascular coupling between the neuronal and the hemodynamic responses, and the characteristics of the hemodynamic response itself [49].…”

Using the Placebo Effect to Isolate Control Mechanisms of Athletic Performance: A Research Protocol

“…Several studies have shown that these wireless NIRS devices produce nearly artifact free and reproducible data. 70 fNIRS can measure changes in O 2 saturation both centrally on the level of the cortex and peripherally at the level of muscles. Further, it is portable and not easily susceptible to movement artifacts.…”