Brain Size Changes With Time Of Day, Finds 10,000 Brain Scans

Weird fact about how our brains change size over a single day.

Weird fact about how our brains change size over a single day.

The human brain is biggest in the morning and gets smaller as the day progresses.

By tomorrow morning, though, it will be back to its ‘full’ size.

The conclusions come from a study of thousands of brain scans carried out to investigate Alzheimer’s disease and multiple sclerosis.

Scientists found that people generally had the biggest brains in the morning and they shrank progressively into the afternoon and evening.

The total amount of shrinkage is not that great: certainly less than 1% and probably closer to 0.3%.


The study’s authors write:

“A possible mechanism may be that lying down during the night is associated with a redistribution of body fluids that had accumulated in the lower extremities during the day.

It is also possible that the effect of time-of-day is associated with hydration status.”

The study was published in the journal Neuroimage (Nakamura et al., 2015).

Brain image from Shutterstock

Author: Dr Jeremy Dean

Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology. He has been writing about scientific research on PsyBlog since 2004.

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