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Review
. 2016 Mar 15:35:9.
doi: 10.1186/s40101-016-0091-9.

Light-sensitive brain pathways and aging

V Daneault  1   2   3 , M Dumont  4 , É Massé  5   4 , G Vandewalle  6   7 , J Carrier  5   4   6
Affiliations
Review

Light-sensitive brain pathways and aging

V Daneault et al. J Physiol Anthropol. .

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.

Keywords: Aging; Brain; Light; Non-image-forming (NIF) functions.

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Figures

Fig. 1
Fig. 1
Light-sensitive brain pathways. Simplified brain networks (not exhaustive representation) of the classical visual system and the non-image-forming system. Abbreviations: PFC prefrontal cortex, SCN suprachiasmatic nucleus, SPVZ subparaventricular zone, VLPO ventrolateral preoptic nucleus, PVN paraventricular nucleus of the hypothalamus, LH lateral hypothalamus, DMH dorsomedial nucleus of the hypothalamus, LGN lateral geniculate nucleus, IGL intergeniculate leaflet, EWN Edinger-Westphal nucleus, OPN olivary pretectal nucleus, SC superior colliculus, V1 primary visual area, LC locus coeruleus, VTA ventral tegmental area, ipRGC intrinsically photosensitive retinal ganglion cell, RHT retino-hypothalamic tract. Eye illustration components modified from: http://2012books.lardbucket.org/books/beginning-psychology/s08-02-seeing.html —reproduction/modifications in accordance with: http://creativecommons.org/licenses/by-nc-sa/3.0/ Brain template: reproduced with permission from McGraw-Hill Education Material (source: Saladin, Kenneth S., Human Anatomy, Edition: 2, ISBN: 9780072943689, Figure 15.2-b, p. 425)
Fig. 2
Fig. 2
Steady-state pupil constriction in young and older individuals. Mean pupillary constriction relative to baseline ± SEM in each age group. Blue bars: blue light at low (L), medium (M), and high (H) irradiances. Green bars: green light at low (L), medium (M), and high (H) irradiances. Effects of wavelength and irradiance levels were significant (*p < 0.05), but there was no difference between age groups and no interaction with age (n.s. not significant). Reproduced with permission from [116]
Fig. 3
Fig. 3
Effect of the presence of light on brain responses of younger and older individuals performing an auditory two-back task. Statistical results (p < 0.001 uncorrected) overlaid over the mean structural image of all participants. Significant responses to light are displayed in yellow for younger individuals (Y), in red for older individuals (O), whereas group differences (Y > O) are in blue. Right panels a-l show activity estimates (arbitrary unit (a.u.) ± standard error of the mean) in each brain region. *Significantly activated, p < 0.05 corrected for multiple comparisons over small volumes of interest; # significant group differences, p < 0.05 corrected for multiple comparisons over small volumes of interest. Abbreviations: a LGN lateral geniculate nucleus, b LING lingual gyrus, c CALC calcarine sulcus, d MOG/SOG middle and superior occipital gyrus, e FPC frontopolar cortex, f THAL dorsomedian thalamus, g PULV thalamus pulvinar, h INSULA insula, i AMYG amygdala, j TEGM tegmentum, k CEREB cerebellum, l OPERC frontal operculum. Please refer to Table 2 of [113] for brain clusters coordinates. Reproduced with permission from [117]
Fig. 4
Fig. 4
Effect of irradiance level of light on brain responses of younger and older individuals performing an auditory two-back task. Statistical results (p < 0.001 uncorrected) overlaid over the mean structural image of all participants. Significant changes in responses as a function of irradiance level are displayed in yellow for younger individuals (Y) and in red for older individuals (O), whereas group differences (Y > O) are in blue. Panels a–e represent estimates [a.u. ± standard error of the mean (SEM)] of the brain responses while exposed to blue light independent of the irradiance change. Panels f–j represent estimates (a.u. ± SEM) of the linear change in brain responses with change in irradiance level. Panels k–o consist of a schematic representation of the composite of both components (responses to light and irradiance change) showing the evolution of the responses with change in irradiance level. Panels m–o only includes younger  individuals because responses were not significantly affected by irradiance change in older individuals in the brain regions considered. *Significantly activated, p < 0.05 corrected for multiple comparisons over small volumes of interest; #significant group differences, p < 0.05 corrected for multiple comparisons over small volumes of interest; n.s. non significant group difference. Abbreviations: a & f CALC calcarine sulcus, b, e, g, & j IOG/MOG/SOG inferior/middle/superior occipital gyrus, c & h FPC frontopolar cortex, d & i CEREB cerebellum. Please refer to Table 3 of [113] for brain clusters coordinates. Reproduced with permission from [117]
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