Individual Differences in Hemodynamic Responses Measured on the Head Due to a Long-Term Stimulation Involving Colored Light Exposure and a Cognitive Task: A SPA-fNIRS Study.

Hamoon Zohdi,Felix Scholkmann,Ursula Wolf

doi:10.3390/brainsci11010054

Hamoon Zohdi, Felix Scholkmann + Show 1 more

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https://doi.org/10.3390/brainsci11010054

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Abstract

When brain activity is measured by neuroimaging, the canonical hemodynamic response (increase in oxygenated hemoglobin ([O2Hb]) and decrease in deoxygenated hemoglobin ([HHb]) is not always seen in every subject. The reason for this intersubject-variability of the responses is still not completely understood. This study is performed with 32 healthy subjects, using the systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) approach. We investigate the intersubject variability of hemodynamic and systemic physiological responses, due to a verbal fluency task (VFT) under colored light exposure (CLE; blue and red). Five and seven different hemodynamic response patterns were detected in the subgroup analysis of the blue and red light exposure, respectively. We also found that arterial oxygen saturation and mean arterial pressure were positively correlated with [O2Hb] at the prefrontal cortex during the CLE-VFT independent of the color of light and classification of the subjects. Our study finds that there is substantial intersubject-variability of cerebral hemodynamic responses, which is partially explained by subject-specific systemic physiological changes induced by the CLE-VFT. This means that both subgroup analyses and the additional assessment of systemic physiology are of crucial importance to achieve a comprehensive understanding of the effects of a CLE-VFT on human subjects.

Highlights

Colored light modulates a wide range of functions in human physiology, including the sleep-wake cycle via melatonin secretion, alertness, cognition, and thermoregulation [1,2]
There are three possible explanations for the observed correlation between functional near-infrared spectroscopy (fNIRS) signals, namely, [O2Hb], and systemic physiology, such as SpO2 and mean arterial pressure (MAP). (i) The fNIRS signals of the brain are caused by changes in systemic physiology. (ii) The systemic physiological changes are caused by brain activity. (iii) The fNIRS signals reflect neurovascular coupling (NVC) only, and the correlation we found between [O2Hb] and systemic physiology has no causal relation
We found that red light exposure led to better performance of subjects taking the verbal fluency task (VFT), while simultaneously showing a physiological response of higher oxygenation in the left prefrontal cortex (PFC) than the right

Summary

Introduction

Colored light modulates a wide range of functions in human physiology, including the sleep-wake cycle via melatonin secretion, alertness, cognition, and thermoregulation [1,2]. Since the discovery of the photopigment melanopsin nearly two decades ago, non-imageforming (NIF) vision has been focused on as a potential explanation for a number of effects of colored light on human physiology [3,4]. This light-sensitive protein is expressed in a subclass of intrinsically photosensitive retinal ganglion cells and is most sensitive to narrowband blue light (~460−480 nm) [5,6]. The effects of colored light on alertness and cognitive performance beyond the scope of NIF vision responses are not yet well understood. Previous studies demonstrated that improvements in cognitive performance via colors or colored light depend on the environment and certain situational variables, and on the individual subject, as well as the type of cognitive task [13,14,15,16]

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