Abstract
The idea that light affects mood and behavioral state is not new. However, not much is known about the particular mechanisms and circuits involved. To fully understand these, we need to know what properties of light are important for mediating changes in mood as well as what photoreceptors and pathways are responsible. Increasing evidence from both human and animal studies imply that a specialized class of retinal ganglion cells, intrinsically photosensitive retinal ganglion cells (ipRGCs), plays an important role in the light-regulated effects on mood and behavioral state, which is in line with their well-established roles in other non-visual responses (pupillary light reflex and circadian photoentrainment). This paper reviews our current understanding on the mechanisms and paths by which the light information modulates behavioral state and mood.
Highlights
Light is a powerful multifaceted stimulus; aside from supporting vision, light affects a range of physiological and behavioral aspects
These effects are typically described as being most effectively elicited by ‘brighter’ and ‘bluer’ lights and have been described first as primarily responses to changes in ambient illumination, and second, as likely to originate with a particular class of retinal neurons so-called intrinsically photosensitive retinal ganglion cells. ipRGCs have the extraordinary capacity of responding to light directly thanks to their expression of the photopigment melanopsin
Based on our recent knowledge from mouse models on NV responses including the pupillary light reflex and circadian photoentrainment, it is possible that inputs from the rods and cones play roles in driving the light effect on mood and behavioral state
Summary
Light is a powerful multifaceted stimulus; aside from supporting vision, light affects a range of physiological and behavioral aspects. Functional imaging and psychometric assessments indicate that light can affect mood, alertness/attention and cognitive performance in humans [1]. These effects are typically described as being most effectively elicited by ‘brighter’ and ‘bluer’ lights and have been described first as primarily responses to changes in ambient illumination, and second, as likely to originate with a particular class of retinal neurons so-called intrinsically photosensitive retinal ganglion cells (ipRGCs). Recent studies in mice have started to elucidate the mechanisms and circuits for mediating these light effects driven by ipRGCs. Understanding how light affects mood has a direct practical implication on the health and well-being of people, especially more than ever given that people spend most of their time indoors exposed to artificial lighting of various qualities that can be controlled. Useful new perspectives on the control of mood by understanding the mechanisms of light input may gain deeper insights into the general control of mood and reveal new therapeutic approaches for mood disorders
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