New research reveals how lack of sleep impairs the brain’s ability to suppress unwanted memories, highlighting the essential role of REM sleep.
Study: Memory control deficits in the sleep-deprived human brain. Image credit: lightpoet/Shutterstock.com
In a recent study published in the Psychological and cognitive sciencesA group of researchers studied how sleep deprivation impairs inhibitory control of memory and contributes to intrusive memories, focusing on the role of rapid eye movement (REM) sleep in restoring this function.
Background
Intrusive memories of unpleasant experiences can have a significant impact on mental health, particularly in conditions such as depression, anxiety and post-traumatic stress disorder. Removing these memories helps weaken their impact, thereby reducing future intrusions and making emotional regulation easier.
This process depends on effective cognitive control, mediated by brain regions such as the right dorsolateral prefrontal cortex (rDLPFC), which suppresses hippocampal memory retrieval.
Sleep, particularly REM sleep, is crucial for restoring this mechanism, but its precise role remains unclear. Further research is essential to clarify the impact of sleep disruption on the neural and cognitive processes underlying memory suppression and its broader effects on emotional well-being.
About the study
Eighty-seven healthy adults aged 18 to 30 participated in a study examining the effects of sleep deprivation on memory suppression. Participants were right-handed, native English speakers, with no history of neurological, psychiatric, or sleep disorders.
They reported regular waking hours of 8:00 a.m. and at least six hours of sleep per night. Written informed consent was obtained from all participants and they were compensated with £80 or academic credit.
Two participants were excluded for non-compliance with the study protocol, leaving a final sample of 85. Participants were randomly assigned to either a sleep deprivation group (n = 43) or a sleep group. repairer (n = 42).
Participants performed cognitive and affective tasks during two sessions: one in the evening and one the next morning. The sleep-deprived group remained awake under supervision, while the rested group was given an eight-hour sleep opportunity monitored by polysomnography (PSG). Compliance with the protocol was confirmed using actigraphic wristwatches.
The tasks included memory encoding and suppression exercises, magnetic resonance imaging (MRI) scans, and affective assessments. Functional MRI (fMRI) assessed brain activity, while behavioral scans revealed impaired memory suppression in the sleep-deprived group, with higher rates of intrusion than in the rested group.
These results highlight the crucial role of sleep, particularly REM sleep, in enabling effective memory control.
Study results
Lack of sleep significantly impairs the brain’s ability to suppress intrusive memories. After a night of sleep deprivation (n = 43, mean age 19.58 years) or restorative sleep (n = 42, mean age 20.33 years), participants performed the Think/Don’t Think (TNT) task. while undergoing fMRI. In this task, participants actively retrieved or suppressed memories associated with visual cues.
We tracked deletion attempts that failed and led to memory intrusions. Behavioral analyzes revealed that while suppression reduced intrusions over time for all participants, sleep-deprived individuals showed a slower reduction, reflecting impaired suppression of adaptive memory.
Interestingly, this impairment was not influenced by the emotional valence of the memories. However, baseline differences in memory control ability between groups partly explained these results.
Sleep-deprived participants performed better on preliminary tasks before nighttime, which may have influenced later results.
Nevertheless, during the final blocks of trials, the difference in intrusion rates between groups disappeared, suggesting that sleep deprivation primarily hinders improvement in suppression over time rather than overall ability to deletion.
Heart rate variability (HRV), particularly the high-frequency component (HF-HRV), was examined to explore the physiological correlates of memory control. In the sleeping group, higher HF-HRV was linked to better suppression, while in sleep-deprived individuals, higher HF-HRV was unexpectedly correlated with poorer suppression, suggesting that the benefits of HF-HRV depend on sufficient sleep.
Neuroimaging data further highlighted the impact of sleep deprivation. The rDLPFC, a region crucial for memory suppression, showed reduced activation in the sleep-deprived group.
Meanwhile, the right hippocampus, typically deactivated during suppression, exhibited diminished disengagement, indicating disruption of memory control circuits. Whole-brain analyzes confirmed these findings, with reduced prefrontal control and increased hippocampal activity following sleep deprivation.
REM sleep plays a restorative role. In the restorative sleep group, longer REM sleep duration was associated with stronger rDLPFC activity during memory suppression, further supporting its role in restoring prefrontal control.
Sleep deprivation also disrupted the functional segregation of brain networks, with increased connectivity between the default mode network (DMN) and the cognitive control network (CCN) and reduced DMN-thalamus connectivity, impairing adaptive control.
Finally, thought patterns were assessed using a multidimensional experience sampling method. Sleep-deprived participants reported fewer deliberate, task-focused thoughts, reflecting a broader breakdown in cognitive control.
Conclusions
To summarize, sleep deprivation significantly disrupts inhibitory control of memory, impacting higher-order cognitive functions. Sleep-deprived participants showed impaired engagement of the rDLPFC during memory suppression, thereby reducing their ability to downregulate unwanted memories over time.
In contrast, restorative sleep, particularly longer duration of REM sleep, was associated with enhanced rDLPFC activation, promoting prefrontal memory control.
Sleep deprivation also alters functional connectivity between brain networks, increasing DMN and CCN connectivity and reducing DMN-thalamus interactions. These disruptions coincided with less deliberate thinking and highlighted the essential role of sleep in regulating memory and thought processes.
