PLOS bio: Time of day is associated with paradoxical reductions in global signal fluctuation and functional connectivity (2020) Orban et al.

Ravn · Feb 22, 2020

Csaba Orban , Ru Kong, Jingwei Li, Michael W. L. Chee, B. T. Thomas Yeo
Published: February 18, 2020- Open access
https://doi.org/10.1371/journal.pbio.3000602

Abstract

The brain exhibits substantial diurnal variation in physiology and function, but neuroscience studies rarely report or consider the effects of time of day.

Here, we examined variation in resting-state functional MRI (fMRI) in around 900 individuals scanned between 8 AM and 10 PM on two different days.

Multiple studies across animals and humans have demonstrated that the brain’s global signal (GS) amplitude (henceforth referred to as “fluctuation”) increases with decreased arousal.

Thus, in accord with known circadian variation in arousal, we hypothesised that GS fluctuation would be lowest in the morning, increase in the midafternoon, and dip in the early evening. Instead, we observed a cumulative decrease in GS fluctuation as the day progressed. Although respiratory variation also decreased with time of day, control analyses suggested that this did not account for the reduction in GS fluctuation.

Finally, time of day was associated with marked decreases in resting-state functional connectivity across the whole brain. The magnitude of decrease was significantly stronger than associations between functional connectivity and behaviour (e.g., fluid intelligence).

These findings reveal time of day effects on global brain activity that are not easily explained by expected arousal state or physiological artefacts.

We conclude by discussing potential mechanisms for the observed diurnal variation in resting brain activity and the importance of accounting for time of day in future studies.
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We recommend reporting time of day of fMRI scans and other experimental protocols and measurements. Even if all participants are scanned at the same time slot within a particular study, reporting time of day could potentially account for between-study variation in results and failed replications. Meta-analyses could also then be leveraged to explore how time of day affects various regions, networks, and tasks across different domains of the literature.
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Article about the study: How the time of day affects global brain fluctuations?
By Pranjal Mehar February 19, 2020
https://www.techexplorist.com/time-day-affects-global-brain-fluctuations/30170/

TheBassist · Feb 22, 2020

I’ve ling been interested in this. Age is a big factor too. We’re killing our teenagers potential with school times

TheBassist · Feb 22, 2020

This stuff goes right back to the origins of the species.

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PLOS bio: Time of day is associated with paradoxical reductions in global signal fluctuation and functional connectivity (2020) Orban et al.

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