Light-sensitive brain pathways and aging.

V Daneault,G Vandewalle,J Carrier,M Dumont,É Massé

doi:10.1186/s40101-016-0091-9

Abstract

Notwithstanding its effects on the classical visual system allowing image formation, light acts upon several non-image-forming (NIF) functions including body temperature, hormonal secretions, sleep-wake cycle, alertness, and cognitive performance. Studies have shown that NIF functions are maximally sensitive to blue wavelengths (460–480 nm), in comparison to longer light wavelengths. Higher blue light sensitivity has been reported for melatonin suppression, pupillary constriction, vigilance, and performance improvement but also for modulation of cognitive brain functions. Studies investigating acute stimulating effects of light on brain activity during the execution of cognitive tasks have suggested that brain activations progress from subcortical regions involved in alertness, such as the thalamus, the hypothalamus, and the brainstem, before reaching cortical regions associated with the ongoing task. In the course of aging, lower blue light sensitivity of some NIF functions has been reported. Here, we first describe neural pathways underlying effects of light on NIF functions and we discuss eye and cerebral mechanisms associated with aging which may affect NIF light sensitivity. Thereafter, we report results of investigations on pupillary constriction and cognitive brain sensitivity to light in the course of aging. Whereas the impact of light on cognitive brain responses appears to decrease substantially, pupillary constriction seems to remain more intact over the lifespan. Altogether, these results demonstrate that aging research should take into account the diversity of the pathways underlying the effects of light on specific NIF functions which may explain their differences in light sensitivity.

Highlights

Two functional systems detecting light: photoreceptor contribution and neural pathways From a functional point of view, there are two systems detecting light in mammals and humans
Melanopsin retinal ganglion cells In the course of the year 2000s, the discovery of melanopsin (OPN4)-photosensitive pigment expressed by intrinsically photosensitive retinal ganglion cells contributed to a better understanding of the neural bases of the NIF system [6]
These anatomical differences support the possibility of variations in the age-related changes in effects of light on various NIF functions, sustained for instance by the olivary pretectal nucleus (OPN) (PLR) or the suprachiasmatic nuclei (SCN)

Summary

Introduction

Two functional systems detecting light: photoreceptor contribution and neural pathways From a functional point of view, there are two systems detecting light in mammals and humans. These studies confirmed that in young subjects, light exposure, blue light, has greater modulating effects on cognitive brain functions than other light wavelengths most likely through melanopsin photoreception and triggers brain activation increases in regions related to alertness and to executive functions (for a review, see [5, 76]).

Results

Conclusion