A quantitative comparison of fMRI and fNIRS activity to a median nerve stimulation task
Functional Magnetic Resonance Imaging (fMRI) and functional Near Infrared Spectroscopy (fNIRS) are neuroimaging techniques that can measure changes in blood flow in response to external stimuli. fNIRS is a portable imaging device and considered to be the optical equivalent of fMRI. The objective of this preliminary work is to investigate the ability of fNIRS to detect brain activity during a median nerve stimulation task in healthy controls and to compare the results to fMRI findings. To date, 25 healthy controls have been recruited to the fMRI task, of which 10 have also participated in the fNIRS task. Median nerve stimulation was conducted while brain activity was recorded with fMRI and fNIRS (tests done sequentially). Both the left and right hand were stimulated, successively, at a current that sustained thumb abduction (8-35 mA). A block design with eight cycles of stimulation 'on' and seven cycles of 'rest' was used. At the group level, for both fMRI and fNIRS, significant brain activity was observed in the contralateral primary and bilateral secondary somatosensory areas for each hand being stimulated. At the single subject level, the results demonstrate an 80% agreement between fMRI and fNIRS results where fMRI is considered ground truth. The overall good agreement between the two techniques is promising, and future work will focus on recruiting additional participants to better assess the sensitivity between modalities. Ultimately, this work adds to the growing body of research highlighting fNIRS as a suitable alternative to fMRI, as it affords the advantage of being portable and low-cost to maintain.