False positives and false negatives in functional near-infrared spectroscopy: issues, challenges, and the way forward

Abstract

We highlight a significant problem that needs to be considered and addressed when performing functional near-infrared spectroscopy (fNIRS) studies, namely the possibility of inadvertently measuring fNIRS hemodynamic responses that are not due to neurovascular coupling. These can be misinterpreted as brain activity, i.e., "false positives" (errors caused by wrongly assigning a detected hemodynamic response to functional brain activity), or mask brain activity, i.e., "false negatives" (errors caused by wrongly assigning a not observed hemodynamic response in the presence of functional brain activity). Here, we summarize the possible physiological origins of these issues and suggest ways to avoid and remove them.

Keywords: functional near-infrared spectroscopy; hemodynamic response.

Fig. 1

Visualization of the six components of the fNIRS signals ([O₂Hb], [HHb], [tHb]). (a) An erroneous assumption is that the fNIRS signal represents only changes associated with functional brain activity due to neurovascular coupling. (b) In reality, the fNIRS signals comprise six components so that five components are potentially confounders in every fNIRS study. The contribution of the components to the fNIRS signal is visualized by color-coding (red: 100%, white: 0%). The nonevoked/cerebral/neuronal and nonevoked/cerebral/systemic components can contribute to the fNIRS signal to a significant degree; however, the evoked changes can be generally stronger in an experimental paradigm assessing functional, task-related, brain-activity.