I spent a bit of time reviewing this research article, 'Sleep duration is associated with white matter microstructure and cognitive performance in healthy adults'. The findings are interesting and give me some direction in terms of my experimentation here. Essentially, sleep duration is more important than sleep quality in terms of cognitive performance.
Here's the Abstract:
Reduced sleep duration and sleep deprivation have been associated with cognitive impairment as well as decreased white matter integrity as reported by experimental studies. However, it is largely unknown whether differences in sleep duration and sleep quality might affect microstructural white matter and cognition. Therefore, the present study aims to examine the cross‐sectional relationship between sleep duration, sleep quality, and cognitive performance in a naturalistic study design, by focusing on the association with white matter integrity in a large sample of healthy, young adults. To address this, 1,065 participants, taken from the publicly available sample of the Human Connectome Project, underwent diffusion tensor imaging. Moreover, broad cognitive performance measures (NIH Cognition Toolbox) and sleep duration and quality (Pittsburgh Sleep Quality Index) were assessed. The results revealed a significant positive association between sleep duration and overall cognitive performance. Shorter sleep duration significantly correlated with fractional anisotropy (FA) reductions in the left superior longitudinal fasciculus (SLF). In turn, FA in this tract was related to measures of cognitive performance and was shown to significantly mediate the association of sleep duration and cognition. For cognition only, associations shift to a negative association of sleep duration and cognition for participants sleeping more than 8 hr a day. Investigations into subjective sleep quality showed no such associations. The present study showed that real‐world differences in sleep duration, but not subjective sleep quality are related to cognitive performance measures and white matter integrity in the SLF in healthy, young adults.
And some excerpts from a section at the end titled, 'Discussion':
To our knowledge, this is the first study to investigate the relationship between subjective sleep quality, sleep quantity, cognitive performance, and white matter microstructure in a well‐powered sample of healthy, young adults. Our findings demonstrate that reported sleep duration, but not subjective sleep quality is associated with both cognitive performance, especially in language subdomains, and white matter integrity of the SLF irrespective of age, sex, or BMI. Moreover, the mediation analysis showed that white matter microstructure mediated the association of sleep duration and cognitive performance. Taken together, our results suggest that cognition and white matter integrity are not only affected by experimental sleep deprivation but are also associated with natural differences in habitual sleep duration.
The findings of the present study are in line with other studies, which showed that cognitive performance and white matter are associated with sleep duration. A previous study demonstrated that only objective total sleep time, but not subjective sleep indices predicted memory performance in community‐based older adults (Cavuoto et al., 2016). In contrast, other studies demonstrate that neither subjective nor objective measures of sleep (measured with the PSQI) are associated with cognitive performance in elderly participants (Blackwell et al., 2011; Saint Martin et al., 2012). We did not find any interactions with age in our analyses, but as the mean age is comparably low (mean age = 28.8) and the age range (22–37 years) is restricted in our sample, future studies with larger samples across the whole lifespan should investigate age‐related differences in the association of sleep duration and brain structure and function to address these heterogeneous findings. Previous findings of a nonlinear (quadratic) relationship between sleep duration and cognition could be replicated with the present sample. Our exploratory analyses revealed a negative U‐shaped association of sleep duration with cognition. Nonetheless, the coefficient on the linear sleep duration regressor remained significant in this model as well, suggesting a stronger association of reduced sleep duration with cognition compared to increased sleep duration. In line with that, statistical analyses in which our sample was divided into subsamples based on sleep duration validate the finding of an inverse U‐shaped association. Although increased sleep duration is negatively associated with cognition, the association of sleep duration with cognition is positive for short and moderate (recommended (Hirshkowitz et al., 2015)) sleep durations. As there is no clear biological hypothesis linking prolonged sleep duration and cognition yet (Marshall & Stranges, 2010), questions remain whether this cross‐sectional observation of prolonged sleep duration and impaired cognition in this comparatively small group (n = 55) could also be the result of comorbid risk factors (Patel, Malhotra, Gottlieb, White, & Hu, 2006). In contrast, our nonlinear analysis revealed no significant association of the coefficient estimate for the squared sleep duration regressor with fractional anisotropy in the SLF.
To conclude, our findings suggest an association of short and long sleep durations with cognitive performance and an association of shorter sleep duration with decreased integrity of white matter microstructure. Considering the growing incidence of sleep problems in western societies, the present study points toward the possible importance of recommended nighttime sleep for healthy brain structure and function.
So basically it's likely really important for me to nail my 'cut off times' so that I give myself the best change for high cognitive performance (lol) each day. :)