Abstract
.Several functional near-infrared spectroscopy (fNIRS) studies report their findings based on changes of a single chromophore, usually concentration changes of oxygenated hemoglobin ([]) or deoxygenated hemoglobin (HHb). However, influence of physiological actions may differ depending on which element is considered and the assumption that the chosen measure correlates with the neural response of interest might not hold. By assessing the correlation between [] and [HHb] in task-evoked activity as well as resting-state data, we identified a spatial dependency of non-neuronal hemodynamic changes in the anterior temporal region of the human head. Our findings support the importance of reporting and discussing fNIRS outcomes obtained with both chromophores ([] and [HHb]), in particular, for studies concerning the anterior temporal region of the human head. This practice should help to achieve a physiologically correct interpretation of the results when no measurements with short-distance channels are available while employing continuous-wave fNIRS systems.
Highlights
Functional near-infrared spectroscopy is an optical neuroimaging technique enabling to quantify changes in hemodynamics and oxygenation within the intracerebral and extracerebral tissue layers of the human head based on the absorption of near-infrared light by the oxygenated (O2Hb) and deoxygenated (HHb) forms of hemoglobin.[1,2]
We report observations that identify a spatial dependency of non-neuronal hemodynamic changes to be of significance for Functional near-infrared spectroscopy (fNIRS) studies: hemodynamics on the anterior temporal region, which might be caused by “head muscles activity,” as recently reported by Volkening et al.[21]
For the dataset with task-evoked data, we evaluated the grand average of the blood volume pulse amplitude (BVPA); and for the resting-state, channel-wise correlation for each chromophore was calculated for all channels as seeds
Summary
Functional near-infrared spectroscopy (fNIRS) is an optical neuroimaging technique enabling to quantify changes in hemodynamics and oxygenation within the intracerebral and extracerebral tissue layers of the human head based on the absorption of near-infrared light by the oxygenated (O2Hb) and deoxygenated (HHb) forms of hemoglobin.[1,2] Similar to functional magnetic resonance imaging (fMRI) and its blood-oxygen-leveldependent (BOLD) signal, the inference on neural activation relies on the principle of neurovascular coupling and a close relation with changes in cerebral blood flow.[3]. Different studies have shown that for a proper measure of O2Hb and HHb, two wavelengths are general enough to yield meaningful measures when properly could be an indicator of hemodynamic changes not evoked by neural activity, happening in the intracerebral and/or extracerebral tissues.[13,14] Tachtsidis and Scholkmann[15] recently summarized different physiological sources that may lead to false positives and false negatives in fNIRS measures and the reality is that the fNIRS signal assumed to always be neuronally evoked may be present in many other physiological components These include changes in partial pressure of carbon dioxide in the arterial blood (PaCO2),[16,17] blood pressure,[18,19] and activity of the sympathetic nervous system.[19,20] As shown
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