A good night’s sleep could be more crucial than we think. It might seem like an unattainable goal to some — something we never get enough of, as we feel the unpleasant effects from a lack of it. Now those effects might run deeper than anyone previously thought possible. Recent research published by the journal Human Brain Mapping suggests that there is a growing body of evidence to suggest that routine differences in our sleep habits — the difference between whether you’re the type who sleeps a consistent seven or eight hours a night, or someone who thinks they can get by with fewer hours of sleep — can account for differences within our own brain structures. These differences are consequently responsible for how we function cognitively.
“Generally, we are interested in microstructural changes of white matter fiber connections, which are responsible for the transfer of information between different brain regions,” says the study’s main co-author Pascal Grumbach, who is a medical student and a member of the Neuroplasticity and Neuromodulation Research Group at Muenster University Hospital. Grumbach’s study demonstrates a decreased integrity of the brain’s white matter structure. Think of the brain’s white matter as the insulation for all of its nerve cell bodies, where neurons jump and send electrical signals to each other. This sheath of myelin continues to grow throughout an individual’s lifetime, peaking when they reach middle age.
Grumbach’s study sought to determine whether things like sleep duration in otherwise healthy human beings were associated with disparity in the brain’s white matter. “To address this unanswered question, we used data from the publicly available Human Connectome dataset,” says Grumbach, referring to the National Institutes of Health’s five-year research effort to build a virtual model of the human brain, while creating a national database to facilitate research on an array of common neurological diseases and disorders.
The data acquired by Grumnach included the brain scans of 1,065 young adults described as healthy. These participants were then given a series of tests to further determine their cognitive functioning and then they answered questions about the quality of their sleep and sleep duration.
“We are working with data from diffusion tensor imaging, which provides imaging and analysis of white matter integrity. Insights into the so-called connectome of the human brain is one major research field of today’s cognitive neuroscience to reveal how the brain structure is enabling higher brain function,” explains Grumbach. He and his research team are looking at how the brain’s map of neural connections can shift due to psychiatric diseases as well as the best possible future therapies.
During their experiment, the researchers discovered that it was sleep duration — and not the subjective quality of sleep — that was linked to the patient’s cognitive performance. This relationship is in part explained by the microstructure of white matter within a specific brain region.
The study made a correlation between shorter sleep duration and decreased white matter integrity in the superior longitudinal fasciculus (SLF), a path that plays a crucial role both in working memory — the memory needed to perform simple tasks in the immediate short term like committing a phone number to memory — and also in language processing.
This was further underlined by the researchers’ results when they found that white matter microstructure in the SLF was consequently associated with how well the test subjects scored on their cognitive performance. By taking a closer look, Grumbach’s team learned that poor cognitive performance was not just associated with a low number of hours spent asleep — but so were unusually long sleeping times.
“While we cannot assess the optimal sleeping duration for an individual, we saw that the strongest cognitive performance was displayed by those, who had an average of 7 to 8 hours of sleep,” Grumbach says, which is largely consistent with expert recommendations for an ideal night’s sleep.
The team’s findings are in line with data from previous research, which also realized a connection between white matter integrity in the SLF and disrupted sleep patterns. The study’s co-authors also set controls for age, sex, as well as body mass index. The new study — as with all research — is not without caveats, however.
As Grumbach emphasizes: “Our results show just an association, meaning that we observed a link between sleep and brain health. We cannot claim that hours spent sleeping has a causal effect on brain structure and function.” Grumbach plans to follow this up in the future with randomized, controlled trials, but he does see some evidence lining up in his favor — since previous studies show this link consistently happening in trials using animals, particularly when it comes to too little sleep.