Poster No:
2485
Submission Type:
Abstract Submission
Authors:
Madeline Daveney1,2,3, Elise McGlashan2,4, Sean Cain1,2, Sharna Jamadar1,2,3
Institutions:
1Monash University, Melbourne, Australia, 2Turner Institute for Brain and Mental Health, Melbourne, Australia, 3Monash Biomedical Imaging, Melbourne, Australia, 4The University of Melbourne, Melbourne, Australia
First Author:
Madeline Daveney, BPsych(Hons)
Monash University|Turner Institute for Brain and Mental Health|Monash Biomedical Imaging
Melbourne, Australia|Melbourne, Australia|Melbourne, Australia
Co-Author(s):
Sean Cain, PhD
Monash University|Turner Institute for Brain and Mental Health
Melbourne, Australia|Melbourne, Australia
Sharna Jamadar, PhD
Monash University|Turner Institute for Brain and Mental Health|Monash Biomedical Imaging
Melbourne, Australia|Melbourne, Australia|Melbourne, Australia
Introduction:
The effect of light on humans ranges from its core role in vision to a wide array of non-visual effects on mood, physiology and brain activity (Chellappa et. al., 2011; McGlashan et. al., 2018; Vandewalle & Dijk, 2013). The non-visual effects of light in humans are thought to be mediated by the intrinsically photoreceptive retinal ganglion cells (ipRGCs) in the retina (Panda et. al., 2002; Schmidt et. al., 2011). ipRGCs contain the photopigment melanopsin, which becomes activated when exposed to light and are preferentially activated by short wavelength (blue) light compared to light of other wavelengths (Do & Yau, 2010). When activated by light, ipRGCs send signals to the brain through the retinohypothalamic tract. The aim of this study was to explore the effect of blue light on brain activity in a task-free, resting state paradigm.
Methods:
Healthy individuals, free from sleep and circadian disorders (n=18, 50% female, age: M = 23.55, SD = 3.77) undertook functional MRI (fMRI) scans as part of the current study. As circadian rhythms show change with age, only participants aged 18 to 30 years were eligible for the study. Light was delivered using a custom-built fibre-optic LED light delivery system fitted to the MRI head coil. Participants were exposed to 30 second alternating blocks of blue-enriched (100 lux) and blue depleted (100 lux) light for a period of eight minutes. Half of the participants received blue-enriched light as their first exposure, and the other half received blue-depleted light as their first light exposure. Structural T1-weighted (TE = 2.07 ms; TR = 2.3 s, field of view: 256 mm; slice thickness: 1 mm) and functional T2*-weighted (TE = 30 ms; TR = 2 s, field of view: 192 mm; slice thickness: 2.2mm, interleaved acquisition) images were acquired. Participants did not engage in any task or activity during the imaging session. SPM12 was used to pre-process and analyse the results. A first-level general linear model and contrasts were computed for each participant to identify brain regions showing: (i) greater activity under blue-enriched compared to blue-depleted light and (ii) greater activity under blue-depleted compared to blue-enriched light. Voxels containing z-statistics with corresponding p-values of less than 0.001 were considered statistically significant. A second-level general linear model was then computed with the same statistical significance thresholds to view group results for both contrasts.
Results:
A cluster of significantly activated voxels (k=48) was found in the left portion of the rostral cingulate zone (z=3.75, p<0.001, MNI coordinates [-8 48 4]). However, the results were not significant at the cluster level (p=0.114). No brain areas showed significantly greater brain activity when exposed to blue-depleted light compared to blue-enriched light.
Conclusions:
The rostral cingulate zone is part of the anterior cingulate cortex. Activity in the anterior cingulate cortex, part of the limbic system, is associated with emotional regulation and various cognitive functions (Kober et. al., 2009; Rolls, 2019; Shackman et. al., 2011). It has also been implicated widely in mood disorder populations (Drevets et. al., 2008). Light exerts powerful positive effects on both mood and cognition and is associated with the activation of brain regions involved in these functions. As the non-visual effects of light - including those on mood and attention - are seen most prominently during blue light exposure, the results of the current study lend further support to this role of light in emotional and cognitive brain activity. Overall, these results provide evidence supporting the role of circadian photoreception in an area of the brain involved in mood, emotion and cognition, and cements the non-visual, non-image forming effects of light in humans at the neural level.
Modeling and Analysis Methods:
Activation (eg. BOLD task-fMRI) 2
Perception, Attention and Motor Behavior:
Perception and Attention Other 1
Keywords:
FUNCTIONAL MRI
Limbic Systems
Other - Blue light; Circadian Photoreception; Non-visual effects of light
1|2Indicates the priority used for review
Provide references using author date format
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Do, M. T. H., & Yau, K. W. (2010). ‘Intrinsically photosensitive retinal ganglion cells’, Physiological reviews, vol. 90, no. 4, pp. 1547-1581.
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