Two-hour naps during night shifts may restore brain function and memory in nurses

A new study suggests that taking a two-hour nap during a night shift may help restore brain function and memory in nurses. The research provides evidence that napping can reverse some of the disruptive effects of sleep deprivation on brain connectivity. These findings were published in the Journal of Sleep Research.

Nursing is a demanding profession that requires round-the-clock patient care. This necessity often forces medical staff to work night shifts, which disrupts their natural sleep-wake cycles. The resulting sleep loss is frequently associated with a decline in cognitive performance.

Previous studies indicate that this cognitive decline can lead to serious consequences. These include a higher risk of workplace accidents, such as needle stick injuries, and an increase in medication errors. Chronic sleep deprivation is also linked to broader health issues like depression, heart disease, and obesity.

Hospitals and researchers have sought effective strategies to mitigate these risks. One common countermeasure is the “nighttime nap,” or a scheduled break for sleep during a shift. While napping is known to reduce sleepiness, the biological mechanisms behind its restorative effects have not been fully understood.

The authors of the current study aimed to map how a nighttime nap affects the brain’s functional organization. They specifically wanted to observe changes in brain connectivity and memory performance following sleep loss. They employed advanced brain imaging techniques to visualize these internal changes.

The study recruited 24 female nurses from the Fujian Medical University Union Hospital in China. The participants were young adults with an average age of approximately 20 years. All subjects were right-handed and reported having good sleep habits prior to the study.

The researchers designed an experiment involving three different monitoring sessions for each nurse. These sessions were spaced out by two to four weeks to prevent any lingering effects from previous trials. The participants stayed at the institution during the sessions to ensure compliance with the protocol.

The first condition was labeled “rested wakefulness.” During this phase, participants followed a normal schedule and slept from midnight to 8:00 a.m. This session served as a baseline for normal brain activity and cognitive function.

The second condition involved total sleep deprivation. The nurses remained awake for 24 continuous hours, starting from 8:00 a.m. on the first day until 8:00 a.m. the next. This session mimicked the physical and mental strain of a challenging night shift without a break.

The third condition was the nighttime nap session. Participants stayed awake for the majority of the 24-hour period but were allowed to sleep for two hours. This nap occurred between 2:30 a.m. and 4:30 a.m., a common time for breaks during night shifts.

Following each of these sessions, the researchers assessed the participants between 8:00 a.m. and 10:00 a.m. They used functional magnetic resonance imaging, or fMRI, to scan brain activity while the nurses lay still with their eyes closed. This method allowed the team to observe the brain’s “resting state.”

The team analyzed the imaging data using a metric called functional connectivity density. This technique quantifies the number of functional connections a specific brain region, or voxel, has with the rest of the brain. A higher density suggests that a region plays a more central role in processing information.

In addition to brain scans, the nurses completed cognitive assessments to measure memory performance. One assessment was the Complex Figure Test. This task required participants to copy a complicated line drawing and then redraw it from memory after a delay.

Another assessment was the California Verbal Learning Test. This tool measures verbal memory by asking participants to recall lists of words immediately and after a waiting period. These tests provided concrete data on how well the nurses could retain and retrieve information.

The study found that performance on these memory tests dropped significantly after the session with total sleep deprivation. The nurses struggled to recall details of the drawings and remembered fewer words from the lists. This decline aligns with established knowledge regarding the impact of fatigue on the brain.

However, the results showed a marked improvement following the nighttime nap session. The nurses performed better on both visual and verbal memory tasks after taking the two-hour nap compared to when they remained awake the whole time. The nap appeared to offer a protective benefit against cognitive lapses.

The fMRI scans revealed that sleep deprivation caused widespread disruptions in brain connectivity. Areas of the brain involved in high-level cognition showed reduced connectivity density. These areas included the frontal and parietal lobes, which are essential for planning and memory.

The reduction in connectivity suggests that the brain exerts less voluntary control when exhausted. The networks responsible for maintaining focus and processing complex tasks became less integrated. This neural breakdown likely explains the poor performance on the memory tests.

Concurrently, regions involved in sensory processing and the thalamus showed increased connectivity during sleep deprivation. The thalamus acts as a relay station for information traveling to the cerebral cortex. The researchers interpreted this increase as a compensatory mechanism.

It appears the brain attempts to maintain alertness by ramping up activity in sensorimotor and visual networks. This heightened state might represent the brain’s effort to fight off sleep and remain responsive to the environment. The brain shifts its resources from complex thinking to basic alertness.

The data indicated that the nighttime nap helped reverse these abnormal connectivity patterns. The brain scans from the nap session looked more like the scans from the rested session. The connectivity in cognitive regions was restored to near-normal levels.

This restoration was particularly evident in the thalamus and the default-mode network. The default-mode network is a system of brain regions active when the mind is at wakeful rest. The nap allowed the brain to exit its hyper-alert compensatory state and return to a balanced functional organization.

The researchers also analyzed the statistical relationship between brain changes and test scores. They found that the degree of restoration in brain connectivity correlated with the improvement in memory performance. Nurses who showed the most “normalized” brain scans also had the best memory scores.

This correlation provides evidence that the recovery of brain networks is the mechanism driving the cognitive benefits of napping. The nap allows the brain to reset its communication pathways. This reset facilitates better information processing and memory retention.

The study has some limitations. The sample consisted entirely of young female nurses. The findings might not apply in the same way to male nurses or older adults.

The sample size was also relatively small, with only 24 participants completing the protocol. Larger studies are needed to confirm these effects across a broader and more diverse population. A larger sample would provide more statistical weight to the findings.

The researchers did not use electroencephalography to measure sleep quality during the nap. While they monitored the participants, they did not have data on sleep stages. Future research should include objective measures of sleep depth to see if sleep quality impacts the degree of brain restoration.

The study focused primarily on memory function using specific tests. Subsequent investigations could examine how naps affect other cognitive abilities necessary for nursing. These might include decision-making under pressure, reaction time, or emotional regulation.

The study, “Restorative Effect of Nighttime Naps on Brain Functional Organisation and Memory in Night Shift Nurses,” was authored by Jia-Hui Lin, Jing-Yi Zeng, Hui-Wei Huang, Yan-Juan Lin, and Hua-Jun Chen.