Gray Matter Volume Correlates of Sleepiness: A Voxel-Based Morphometry Study in Younger and Older Adults

Abstract

Background

Subjectively experienced sleepiness is a problem in society, possibly linked with gray matter (GM) volume. Given a different sleep pattern, aging may affect such associations, possibly due to shrinking brain volume.

Purpose

The purpose of the present study was to investigate the association between subjectively rated sleepiness and GM volume in thalamus, insula, hippocampus, and orbitofrontal cortex of young and older adults, after a normal night’s sleep.

Methods

Eighty-four healthy individuals participated (46 aged 20–30 years, and 38 aged 65–75 years). Morphological brain data were collected in a 3T magnetic resonance imaging (MRI) scanner. Sleepiness was rated multiple times during the imaging sessions.

Results

In older, relative to younger, adults, clusters within bilateral mid-anterior insular cortex and right thalamus were negatively associated with sleepiness. Adjustment for the immediately preceding total sleep time eliminated the significant associations.

Conclusion

Self-rated momentary sleepiness in a monotonous situation appears to be negatively associated with GM volume in clusters within both thalamus and insula in older individuals, and total sleep time seems to play a role in this association. Possibly, this suggests that larger GM volume in these clusters may be protective against sleepiness in older individuals. This notion needs confirmation in further studies.

Keywords:

• brain imaging
• thalamus
• insula
• sleep
• KSS

Data Sharing Statement

The project was preregistered at https://clinicaltrials.gov/ct2/show/NCT02000076 and approved by the Ethics Review board of the Stockholm region (Dnr 2012/1098–31/2). Methods, data, and technical validation have been reported in detail in a previous manuscript.²⁸ All data are available immediately and indefinitely from the openneuro.org repository, doi: 10.18112/openneuro.ds000201.v1.0.3. We share the full deidentified imaging data set. Other data or documents may be obtained on request from the first author.

Acknowledgments

This work was supported by the Tercentenary Fund of Bank of Sweden, the Swedish Brain Foundation, The Swedish Science Council, the Fredrik and Ingrid Thuring Foundation, the AFA insurance company, and Stockholm Stress Center. We are grateful to Diana Cortes, Danielle Cosme and Roberta Nagai for assistance with polysomnography recordings, to Birgitta Mannerstedt Fogelfors for assistance with screening and instructions to participants, to Rouslan Sitnikov and Jonathan Berrebi for assistance with MRI sequences and auxiliary equipment, and to Hannes Ingre for entering sleep diary data into a spreadsheet. An abstract of this paper was presented as a poster presentation with interim findings at the 2018 Conference in Baltimore of the Associated Professional Sleep Societies. The poster’s abstract was published as abstract 0149, page A58 in the journal SLEEP, April 1, 2018 (Oxford Academic Press/Sleep Research Society). https://doi-org.proxy.kib.ki.se/10.1093/sleep/zsy061.148

Author Contributions

All authors made substantial contributions to conception and design, acquisition of data, analysis and interpretation of data, drafting the manuscript, revising the manuscript critically, read and approved the final draft of the manuscript for submission, gave final approval of the manuscript version to be published, and agreed to be accountable for every step of the work published, and agreed to be accountable for all aspects of the work.

Disclosure

None of the authors have declared any conflicts of interest.