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Updated: May 16, 2026
10:16
Human Circadian Phenotyping and Diurnal Performance Testing in the Real World
Published on: April 7, 2020
Morning-evening variation in human brain metabolism and memory circuits
B J Shannon1, R A Dosenbach, Y Su
1Dept. of Radiology, Washington Univ, St. Louis, MO 63104, USA. bshannon@wustl.edu
Journal of Neurophysiology
|December 1, 2012
Summary
Sleep may reorganize brain function daily, particularly memory networks, without increasing brain metabolism. This study explored daily brain organization changes and metabolic costs during wakefulness.
Area of Science:
- Neuroscience
- Sleep Science
- Cognitive Neuroscience
Background:
- Sleep is hypothesized to facilitate synaptic renormalization after synaptic potentiation during wakefulness.
- Wakefulness may alter the brain's resting-state functional organization and increase its metabolic demands.
Purpose of the Study:
- To investigate daily changes in brain functional organization during wakefulness.
- To assess the metabolic cost of prolonged wakefulness.
Main Methods:
- Resting-state functional magnetic resonance imaging (fMRI) was used to measure brain functional organization at different times of day.
- Quantitative positron emission tomography (PET) was employed to measure brain glucose and oxygen consumption.
Main Results:
- Significant, selective alterations in brain functional organization were observed.
- Bilateral medial temporal regions showed distinct connectivity patterns in the morning versus the evening, correlating with memory retrieval networks.
- These organizational changes occurred independently of any increase in brain metabolism.
Conclusions:
- Daily cycles of brain organization, potentially linked to memory consolidation, may occur without a corresponding rise in metabolic cost.
- The findings challenge the assumption that increased synaptic strength during wakefulness necessitates higher brain metabolism for renormalization during sleep.
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