Abstract
Light evokes robust visual and nonvisual physiological and psychological effects in humans, such as emotional and behavioral responses, as well as changes in cognitive brain activity and performance. The aim of this study was to investigate how colored light exposure (CLE) and a verbal fluency task (VFT) interact and affect cerebral hemodynamics, oxygenation, and systemic physiology as determined by systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS). 32 healthy adults (17 female, 15 male, age: 25.5 ± 4.3 years) were exposed to blue and red light for 9 min while performing a VFT. Before and after the CLE, subjects were in darkness. We found that this long-term CLE-VFT paradigm elicited distinct changes in the prefrontal cortex and in most systemic physiological parameters. The subjects’ performance depended significantly on the type of VFT and the sex of the subject. Compared to red light, blue evoked stronger responses in cerebral hemodynamics and oxygenation in the visual cortex. Color-dependent changes were evident in the recovery phase of several systemic physiological parameters. This study showed that the CLE has effects that endure at least 15 min after cessation of the CLE. This underlines the importance of considering the persistent influence of colored light on brain function, cognition, and systemic physiology in everyday life.
Highlights
Light evokes robust visual and nonvisual physiological and psychological effects in humans, such as emotional and behavioral responses, as well as changes in cognitive brain activity and performance
It is crucial to employ the systemic physiology augmented (SPA) functional near-infrared spectroscopy (fNIRS) approach, which relies on the measurement of brain activity with fNIRS along with the assessment of changes in systemic physiology—an approach our research group has been investigating for several years[38,39,41,42]
We found in the current study that colored light exposure (CLE) in combination with verbal fluency task (VFT) evoked responses in the prefrontal cortex (PFC), while only blue light leads to significant changes in the visual cortex (VC) throughout the CLE-VFT
Summary
Light evokes robust visual and nonvisual physiological and psychological effects in humans, such as emotional and behavioral responses, as well as changes in cognitive brain activity and performance. Neuroimaging studies devoted to this topic employed electroencephalography (EEG)[11,16,17], positron emission tomography (PET)[18], and functional magnetic resonance imaging (fMRI)[1,12,19,20,21,22] These human studies showed that light exposure affects cortical areas involved in the cognitive process and improves alertness and cognitive performance. The performance of the test is mainly mediated by temporal, frontal, and parietal c ortices[25,26,27] These cortices can be investigated by functional near-infrared spectroscopy (fNIRS), a neuroimaging technique, which measures changes in cerebral tissue hemodynamics and oxygenation related to alterations in neuronal activity[28,29,30]. SPA-fNIRS is an ideal approach to avoid misinterpretations of fNIRS signals[43] as well as for a complete understanding of how the whole body reacts to task/stimulus paradigms
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