Sleep is an important part of effective cognitive functioning which has been established by many comprehensive studies, although it is not exactly clear how impaired sleep affects different cognitive domains, and how the cognitive effects relate to variations in length of sleep duration.
A global online portal was established for participants to complete a comprehensive demographic questionnaire regarding sleep duration along with 12 tests designed to evaluate cognitive performance. Ultimately complete data was collected from over 10,000 participants of which about half reported sleeping less that 6.3 hours per night.
A reliable U-shaped curved in deficits associated with reasoning and verbal abilities that corresponded with sleep duration was revealed, illustrating more than 8 hours of sleep was just as damaging as less than 6. Sleep duration didn’t effect all forms of cognitive performance: reasoning and verbal abilities were most affected by sleep, while short term memory remained relatively unaffected even by short sleep durations as low as 4 hours. Suggesting that higher order cognitive processes are impacted by less than ideal sleep patterns.
Studies have shown that complete sleep deprivation can disrupt short term and working memory, which seems to be resolved by shorter periods of sleep. More complex cognitive functions such problem solving requires longer and consistent sleep patterns.
A compelling question has been raised by this study as to why longer sleep duration corresponds with decreased cognitive performance; factors such as failing health or depression may lead to sleep in excess of 8 hours, but it remains unclear as to how these factors would inherently explain decreased cognitive performance, according to the researchers.
Researchers have hypothesized that impaired cognition seen in long sleepers is driven by too much sleep; such as longer sleep is associated with longer more intense sleep inertia which has been shown to produce impairments in high level cognitive domains. This study provides the most granular insight into these questions, future investigations will focus in on unknown factors and mechanisms. Researchers suggest that it is best to aim for between 7-8 hours sleep for optimal cognitive function.
