title: Effects of exposure to colored light on cerebral and systemic physiology in humans
Creators: name: Zohdi, Hamoon
Publisher: name: Universität Bern
Year: 2021
Subjects: subject: 610 Medicine &amp; health

description: 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.