New research has found evidence that natural differences in sleep habits are associated with differences in brain structure, which in turn are related to cognitive performance. The study, published in Human Brain Mapping, abnormal sleeping patterns are associated with decreased white matter integrity in a particular area of the brain.
“Generally, we are interested in microstructural changes of white matter fiber connections, which are responsible for the transfer of information between different brain regions,” said study author Pascal Grumbach, a medical student and member of the Neuroplasticity and Neuromodulation Research Group at Muenster University Hospital.
“In this study we were interested whether interindividual behavioral differences (e.g. sleep duration) in healthy people are associated with such white matter alterations. To address this unanswered question, we used data from the publicly available Human Connectome dataset.”
The data included brain scans from 1,065 healthy, young adults. The participants also completed a battery of tests to assess their cognitive functioning and answered questions about their sleep quality and 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. We are focused on how the connectome is altered in psychiatric diseases and how future therapies might address these alterations,” Grumbach explained.
The researchers found that sleep duration — but not subjective sleep quality — was linked to cognitive performance, and this relationship was partially explained by the white matter microstructure in a particular brain region.
“Our study showed that shorter sleep duration is associated with decreased white matter integrity in one major fiber tract, which is called the superior longitudinal fasciculus (SLF). This white matter tract is important for working memory (like keeping a phone number in your mind) and language processing in the brain,” Grumbach told PsyPost.
“This was underlined by our results because white matter microstructure in the SLF was in turn associated with cognitive performance scores. When we looked even closer, we found out that not only very low numbers hours spent sleeping are associated with worse cognitive performance, we also discovered that unusually long sleeping times are also associated with worse cognitive function.”
“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 7-8 hours of sleep,” Grumbach said.
The findings are in line with previous research, which has found an association between the white matter integrity of the SLF and abnormal sleep patterns. Grumbach and his colleagues also controlled for age, sex, and body mass index. But the new study — like all research — includes some caveats.
“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. This needs to be addressed in randomized controlled trials,” Grumbach said.
“However, based on previous results and studies in animal models, we speculate that especially too little sleep can cause alterations in brain chemistry that result in impaired integrity of the brain white matter.”
The study, “Sleep duration is associated with white matter microstructure and cognitive performance in healthy adults“, was authored by Pascal Grumbach, Nils Opel, Stella Martin, Susanne Meinert, Elisabeth J. Leehr, Ronny Redlich, Verena Enneking, Janik Goltermann, Bernhard T. Baune, Udo Dannlowski, and Jonathan Repple.