Abstract
.There is not yet a comprehensive view of how the color of light affects the cerebral and systemic physiology in humans. The aim was to address this deficit through basic research. Since cerebral and systemic physiological parameters are likely to interact, it was necessary to establish an approach, which we have termed “systemic-physiology-augmented functional near-infrared spectroscopy (SPA-fNIRS) neuroimaging.” This multimodal approach measures the systemic and cerebral physiological response to exposure to light of different colors. In 14 healthy subjects (9 men, 5 women, age: years, range: 24 to 57 years) exposed to red, green, and blue light (10-min intermittent wide-field visual color stimulation; blocks of visual stimulation), brain hemodynamics and oxygenation were measured by fNIRS on the prefrontal cortex (PFC) and visual cortex (VC) simultaneously, in addition with systemic parameters. This study demonstrated that (i) all colors elicited responses in the VC, whereas only blue evoked a response in the PFC; (ii) there was a color-dependent effect on cardiorespiratory activity; (iii) there was significant change in neurosystemic functional connectivity; (iv) cerebral hemodynamic responses in the PFC and changes in the cardiovascular system were gender and age dependent; and (v) electrodermal activity and psychological state showed no stimulus-evoked changes, and there was no dependence on color of light, age, and gender. We showed that short-term light exposure caused color-dependent responses in cerebral hemodynamics/oxygenation as well as cardiorespiratory dynamics. Additionally, we showed that neurosystemic functional connectivity changes even during apparently stress-free tasks—an important consideration when using any of the hemodynamic neuroimaging methods (e.g. functional magnetic resonance imaging, positron emission tomography, and fNIRS). Our findings are important for future basic research and clinical applications as well as being relevant for everyday life.
Highlights
To understand the impact of light on human physiology, it is necessary to distinguish between visual and nonvisual effects.Visual effects relate to the processing of the incident light by photoreceptor cells in the retina.[1]
No statistically significant changes were observed for PETCO2, Q, pulse pressure (PP), LF, and Mayer wave amplitude (MWA) (LPFC)
The significant changes, e.g., in mean arterial blood pressure (MAP), respiration rate (RR), heart rate (HR), pulse-respiration quotient (PRQ), and MWA, in our study indicate that our cerebral functional near-infrared spectroscopy (fNIRS) signals may have been influenced by these factors
Summary
Visual effects relate to the processing of the incident light by photoreceptor cells in the retina.[1] The color is directly quantified by the differential responsivity of three types of cones with sensitivity maxima at ∼560 nm (red), ∼530 nm (green), and ∼420 nm (blue).[2] From the photoreceptors, the signals are transmitted to bipolar cells, onto ganglion cells, and via the optic nerve to the visual cortex (VC). One main class includes intrinsically photosensitive retinal ganglion cells (ipRGCs)[3] with a maximum sensitivity in the blue.[4] The ipRGCs transmit signals to the hypothalamus, epithalamus, limbic system, and the midbrain,[5,6,7,8,9] i.e., brain areas involved in regulating the autonomic nervous system (ANS) and oscillatory physiological processes. It is known that ipRGCs play a fundamental role in regulating chronobiological processes in humans, such as circadian based on input received from the ipRGCs about the intensity of blue light.[15,16,17] Knowledge of this mechanism recently triggered numerous studies investigating the potential for diseasepromoting effects of blue light on human physiology.[18,19]
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