Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Bright Morning Light Enhances Parasympathetic Activity at Night: A Pilot Study of Older People with Dementia, without a Pacemaker

Version 1 : Received: 29 December 2022 / Approved: 3 January 2023 / Online: 3 January 2023 (02:27:06 CET)

How to cite: Liu, C.; Kuo, T.B.J.; Jou, J.; Lai, C.L.; Chang, Y.; Liou, Y.M. Bright Morning Light Enhances Parasympathetic Activity at Night: A Pilot Study of Older People with Dementia, without a Pacemaker. Preprints 2023, 2023010001. https://doi.org/10.20944/preprints202301.0001.v1 Liu, C.; Kuo, T.B.J.; Jou, J.; Lai, C.L.; Chang, Y.; Liou, Y.M. Bright Morning Light Enhances Parasympathetic Activity at Night: A Pilot Study of Older People with Dementia, without a Pacemaker. Preprints 2023, 2023010001. https://doi.org/10.20944/preprints202301.0001.v1

Abstract

Bright morning light (BML) entrains the body clock, modulates circadian rhythm, and improves sleep-wake disturbances. However, its impact on the autonomic nervous system (ANS) at night remains unclear. Hence, we investigated the effects of BML exposure on activities of the parasympathetic nervous system (PSNS) and sympathetic nervous system (SNS) at night. This non-randomized controlled pilot study included participants ≥60 years, diagnosed with a type of dementia or cognitive disorder. We excluded participants with pacemakers. The treatment group received 2500 lx BML, whereas the control group received approximately 200 lx of general lighting. We measured the heart rate variability to quantify ANS activity. The treatment group displayed significantly increased high-frequency (HF) power (Roy's largest root=2.44; P<.01) and insignificantly decreased normalized low-frequency (LF%) power. The corresponding low-frequency/high-frequency ratio (LF/HF), insignificant decrease, and cognitive function were correlated with PSNS activity (Roy's largest root=3.92; P<.01), which is effective for moderate dementia. BML exposure reduced SNS activity and enhanced PSNS activity at night, which consequently affected cognitive function. Furthermore, the light washout intervention markedly increased SNS activity at night. BML therapy may be a useful clinical tool for alleviating the deterioration of cognitive function.

Keywords

light therapy; dementia; heart rate variability; cognitive function; parasympathetic; sympathetic

Subject

Medicine and Pharmacology, Neuroscience and Neurology

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