The impact of blue light on emotion, behaviorally and neuroanatomically, in the immediate context and over the lifespan Open Access
Moon, Paul (Summer 2023)
Abstract
Mistimed light, especially blue light, has been proposed to have depressogenic effects in both human and nonhuman subjects, possibly via projections of intrinsically photosensitive retinal ganglion cells (ipRGCs). In this dissertation, I provide evidence across two experiments that blue-enriched light has subtle impacts on mood- and emotion-related behaviors under ecologically informed experimental conditions, and present a pilot study of the neuroanatomical underpinnings of these impacts. In the first experiment, in a facial expression processing paradigm, human participants were more likely to make mistakes towards negative facial expressions while under a broad-spectrum light (i.e., a light that emits substantial blue light) versus a dimmer, warmer light (i.e., a light which does not emit much blue light). In other words, when participants misidentified emotional-social cues, they tended to mistake any expression for a negative expression in an environment that contained blue light. These effects were observed after only a short 20-minute exposure to our lighting paradigms. In the second experiment, a largely diurnal (day-active) species (the Mongolian gerbil, Meriones unguiculatus) was used to model the effects of extended mistimed blue light during the critical period of adolescence. Gerbils were exposed over several weeks to blue light either after “sunset” (beginning of the dark phase, evening blue light) or before “sunrise” (end of the dark phase, morning blue light) or kept in typical colony conditions. Gerbils in the evening blue light condition demonstrated subtle but meaningful behavioral shifts, such that they demonstrated more aggressive behaviors, increased social investigation, and decreases in exploration- or escape-related behaviors in a modified open field and forced swim task. These behaviors do not fully align with our prediction that depressive-like behaviors would increase following long-term exposure to blue light in the evening, but do suggest that atypically timed blue light can impact aggressive and social behaviors and behavioral strategies associated with environmental challenges. In a third, pilot study, we predicted that evening blue light would alter dopaminergic innervation of a structure that has been implicated in depressive shifts, namely the basolateral amygdaloid complex (BLA), but this hypothesis was not supported. The observed changes in social behavior and behavioral strategies in the other tasks, coupled with preliminary evidence for a lack of anatomical effects in the BLA, implicate other structures in the effects of mistimed blue light during adolescence. Behavioral strategies to use energy more efficiently in response to novel stimuli map onto the overall pattern of behavioral effects observed and suggest possible roles for the medial amygdala, hypothalamus, habenular region, and long-term changes in the HPA axis following exposure to atypically timed blue light. Together, the data presented here indicate that mistimed blue light has subtle impacts on the processing of some social stimuli in the short term and, when experienced in extended conditions in adolescence, may induce changes in both social behaviors and behavioral profiles on other tasks associated with mood in animal models. These subtle shifts may in turn be one of many factors that increase the likelihood of the development of mood disorders.
Table of Contents
Evolved visual systems in modern lighting environments. 1
Impacts of mistimed light on mood regulation. 2
Human visual system and retinal projections. 5
Light sensitive structures relevant to mood disorders. 6
Dissertation. 10
Experiment 1: How does blue light impact the processing of emotional cues in human participants over the short term?. 12
Facial expression processing. 15
Current study and predictions. 15
Methods. 16
Demographics. 16
Experimental design. 16
Results. 19
Primary analyses. 19
Mean difference testing. 20
Pattern of errors. 24
Discussion, limitations, and future directions. 29
Lighting. 29
Chronotype. 34
Conclusion – experiment 1. 36
Experiment 2: Behavioral impacts of blue lighting on mood and emotion over critical developmental periods. 37
Issues within animal studies of light on mood and emotion. 39
The Mongolian gerbil (Meriones unguiculatus) 40
Gerbil visual pathways relevant to mood and emotion regulating regions. 41
Gerbil developmental periods. 42
Types of lighting manipulations used in studies of light’s impact on behavior. 42
Current study and predictions. 43
Methods. 44
Animals. 44
Light manipulations. 45
Behavioral tests. 50
Sucrose preference. 50
Social approach. 52
Elevated plus maze. 52
Modified open field test 53
Modified intruder test 54
Forced swim test 55
Results. 56
Strategy for behavioral analyses. 56
Discussion, limitations, and future directions. 63
Aggressive and social behaviors. 64
Depressive-like behaviors. 65
Potential HPA involvement – energy consumption. 68
Possible impacts of sleep on observed behavioral effects. 70
Limitations and future directions. 72
Conclusion – experiment 2. 74
Pilot study: Organizational impacts of blue lighting on a structure critical for mood and emotion regulation over critical developmental periods. 75
The amygdala in depression. 77
Neurotransmitter (NT) systems affected by depression. 78
Current study and predictions. 82
Methods. 83
Animals. 83
Light manipulations. 84
Histology. 84
Results. 86
BLA.. 87
BLP. 87
Ratio of average of BLA/BLP. 88
Discussions, limitations, and future directions. 89
Conclusion – pilot study. 91
General Dissertation Discussion. 93
Possible alternative pathways involved in behavior impacts of lighting. 95
General limitations and future directions. 98
Teasing apart retinal projections responsible for behavioral effects. 98
Conclusion. 100
References 102
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