‘Sleep inertia’ from short naps linked to reduced connectivity between brain networks
Entering deep sleep and then waking up before completing the normal sleep cycle can result in a phenomenon known as sleep inertia. New brain scan research in NeuroImage helps explain why this phenomenon is associated with reduced cognitive performance.
“My former PhD advisor (Dr. Perrine Ruby) and I were initially interested in sleep inertia — and what happens in the brain during this transient period — because we wanted to understand how this could relate to the recall or forgetting of dreams, which was at the time the main topic of my PhD,” said study author Raphael Vallat of the Center for Human Sleep Science at the University of California, Berkeley.
“And, while we were planning the study, we realized that there was in fact no study that had previously looked at sleep inertia using a multi-modal approach (i.e. using both electrophysiological (EEG), behavioral and neuroimaging (fMRI) approaches).”
“In other words, while the behavioral aspects of sleep inertia were well-described in the scientific literature, very little work had been done on the neurophysiological correlates of sleep inertia,” Vallat said.
The researchers measured the cognitive functioning and brain activity of 34 participants before and after a 45-minute nap.
They found that cognitive performance, as measured with a mental subtraction task, was reduced shortly after awakening from the nap. Participants who were in a deeper sleep before awakening tended to have even bigger drops in performance. But the negative effects dissipated about 25 minutes after awakening.
This decrease in cognitive performance during sleep inertia was correlated with increased delta brainwave activity. In addition, Vallat and his colleagues found that the functional connectivity between brain networks was strongly disrupted shortly after awakening from the nap.