Reproducibility of fNIRS within subject for visual and motor tasks

Functional Near Infrared Spectroscopy (fNIRS) is becoming a popular metric to noninvasively identify brain activity through assessing changes in oxygenated (HbO) and deoxygenated (HbR) hemoglobin concentration. Several aspects of fNIRS imaging are appealing for clinical applications but the reproducibility of fNIRS signals has yet to be determined over several sessions. To address this, four participants completed at least ten sessions on separate days where they performed Motor and Visual tasks while fNIRS signals were measured from 102 channels spanning the entire head. Reproducibility was quantified as the percentage of significant task related activity occurring across sessions at the channel and source levels (anatomically specific and default head models) via Region of Interest (ROI) and vertex-wise analyses. To improve source localization, digitized optode positions from each session were used with the anatomy specific source localization. Individual differences in reproducibility were present yet task-related changes in HbO were significantly more reproducible over sessions than changes in HbR (F(1, 66) = 5.03, p<0.05). Increased shifts in optode position correlated with less spatial overlap across sessions for each participant. Further steps can be taken to increase the reliability of capturing brain activity with fNIRS by improving upon data acquisition and analysis techniques.