Zohdi, Hamoon (2021). Effects of exposure to colored light on cerebral and systemic physiology in humans. (Thesis). Universität Bern, Bern

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Abstract

Humans in industrialized societies have become independent of the natural day and night cycle due to the invention and use of artificial light. Colored light is an element of everyday life, which affects various human functions. The main aim of this PhD thesis is to comprehensively investigate the effects of exposure to colored light on cerebral and human physiology. To achieve this goal, 201 healthy right-handed adults were recruited for 20 different colored light conditions. By using systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) neuroimaging, each subject was measured 2-4 times on different days resulting in 676 single measurements. The SPA-fNIRS approach combines the measurement of brain activity and systemic physiological changes. fNIRS is a non-invasive neuroimaging technique employed to measure changes in cerebral hemodynamics and oxygenation. There is an interaction between these and changes in systemic physiology: consequently, the SPA-fNIRS generally enables us to identify and understand these interactions. We simultaneously assessed the effects of colored light exposure (CLE) in the visual cortex (VC), prefrontal cortex (PFC) and systemic physiology. Such a comprehensive study has not been carried out yet, and an integrative view of how the color of light affects the brain and systemic physiology is lacking. In general, CLE has relatively long-lasting effects on cerebral and systemic physiology in humans, and yellow light leads to higher brain activation in the PFC than the other colored lights. Yellow CLE is associated with more active and positive emotions, including happiness, joy, hope, and cheerfulness. We also show that long-term colored light exposures induce wavelength-dependent modulations of brain responses in the VC. Violet and blue lights elicit higher changes in cerebral parameters compared to the other colored lights during the CLE and recovery phase. Our results show that CLE affects individual humans differently. In particular, blue light leads to eight different hemodynamic response patterns, while the typical hemodynamic response pattern (increase in oxygenated ([O2Hb]) and decrease in deoxygenated ([HHb]) hemoglobin) is still observed and valid at the group-level analysis. The SPA-fNIRS approach is able to show that systemic and cerebral physiology interact. Experimental findings in most parts of this research display that inter-subject variability of hemodynamic responses is partially explained by systemic physiological changes. The finding of this research that blue light has an activating effect in the VC should be taken into consideration when assessing the impact of modern light sources such as screens and light-emitting diodes (LEDs) on the human body. Our findings that yellow light leads to higher PFC activation be tested as a potentially beneficial tool in chromotherapy, i.e., a complementary medicine method, to balance “energy” lacking in physical, emotional, and mental levels. Although yellow light, i.e., CLE in general term, influences humans in several positive ways, it should be noted that each individual reacts differently to the CLE, implying that colored light therapy has to be also adjusted to each individual. Therefore, further research should clarify which color in CLE benefits whom. In a civilization that is rapidly exposed to new and increasing lighting, the findings of this research are relevant for the scientific community, medical professionals, and society.

Item Type:	Thesis
Granting Institution:	Faculty of Medicine, University of Bern
Dissertation Type:	Cumulative
Date of Defense:	22 June 2021
Subjects:	600 Technology > 610 Medicine & health
Institute / Center:	04 Faculty of Medicine > Medical Education > Institute of Complementary and Integrative Medicine (IKIM)
Depositing User:	Hamoon Zohdi
Date Deposited:	10 Sep 2021 07:54
Last Modified:	10 Sep 2021 08:01
URI:	https://boristheses.unibe.ch/id/eprint/10

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