A Comprehensive Overview of the Neural Mechanisms of Light Therapy

Abstract

Light is a powerful environmental factor influencing diverse brain functions. Clinical evidence supports the beneficial effect of light therapy on several diseases, including depression, cognitive dysfunction, chronic pain, and sleep disorders. However, the precise mechanisms underlying the effects of light therapy are still not well understood. In this review, we critically evaluate current clinical evidence showing the beneficial effects of light therapy on diseases. In addition, we introduce the research progress regarding the neural circuit mechanisms underlying the modulatory effects of light on brain functions, including mood, memory, pain perception, sleep, circadian rhythm, brain development, and metabolism.

Blue light exposure-dependent improvement in robustness of circadian rest-activity rhythm in aged rats

“…The same happened with young rats, as blue light also promoted a decrease in L5 values, further improving rest for these animals. This shows, as postulated in the literature, that blue light is a possible agent in consolidating the sleep phase [63]. Furthermore, the effect after the removal of blue light in the aged rats was not immediate, as L5 values remained lower than in the baseline.…”

“…We observed that aged rats submitted to blue light treatment showed significant changes in locomotor rhythmicity parameters. The same happened with young rats exposed to blue light justifying the strength of light and its influence on the central nervous system, particularly on the CTS [ 63 ]. Here we present our new approach to aging treatment using blue light wavelength, which is effective in treating mood disorders in humans without harming the ocular structures [ 53 , 64 ].…”

“…This can happen even in cases of absence of main photoreceptors such as cones and rods [ 74 ]. The ipRGCs are key players in transmitting blue light information to multiple brain regions, such as the SCN, regulating non-visual brain functions [ 63 ]. It is worth noting that ipRGCs are conserved structures in the retina of several mammalian species, including humans [ 63 ].…”

“…The ipRGCs are key players in transmitting blue light information to multiple brain regions, such as the SCN, regulating non-visual brain functions [ 63 ]. It is worth noting that ipRGCs are conserved structures in the retina of several mammalian species, including humans [ 63 ]. The key role of melanopsin in the non-visual pathway is described, such as pupillary response to light, photoentrainment, photophobia and negative masking of locomotor activity [ 97 ].…”

Exposure to light supresses the activity of the medial and superior amygdala during emotional processing

“…Light therapy is effective in treating several mood disorders (1,2). The underlying mechanisms have not been fully resolved, however, but it is likely to involve the amygdala (38). Considering the connection between the neural pathways involved in emotional and mood regulation (39), we aimed to determine which subpart of the amygdala was affected by light during the processing of emotional stimulation.…”