Sleep debt bad for forming new memory in adolescents
Continuous sleep deprivation for multiple nights can hinder new memory formation in adolescents, which can negatively affect their learning ability, a recent study has found.
“Many adolescents are known to function on a schedule of accumulated sleep debt throughout the school week, and here we show that this leads to an inability to form new memories effectively,” said the researchers led by Professor Michael Chee of Centre for Cognitive Neuroscience at Duke-NUS Graduate Medical School in Singapore.
The parallel-group study randomized 59 adolescents (aged 15–18 years) to either a sleep-restricted group or a control group. After having 9 hours of time in bed (TIB) for two nights at baseline in both groups, the sleep-restricted group had 5 hours of TIB (simulating a demanding school week; n=29) while the control group had 9 hours of TIB (n=30), both for five consecutive nights before being subjected to a picture-encoding task (encoding session). Both groups subsequently underwent three consecutive days of recovery sleep with 9 hours TIB followed by another picture-encoding task, which mixed previous pictures from the encoding session with new pictures (retrieval session).
During the encoding session, the sleep-restricted group scored significantly less in accuracy (p=0.001) and responded slower (573 vs 353 ms; p=0.001) than controls in judging pictures, despite the high proportion of correct response in both groups. [J Sleep Res 2017;doi:10.1111/jsr.12578]
During the retrieval session, the sleep-restricted group also showed significantly poorer recognition (p=0.001) of previous picture shown during the encoding session compared with the controls, although response time was not statistically different between the two groups. This, according to the authors, suggests that “poorer retrieval was not a result of residual sleepiness.”
“[Deficit] to encoding … is not remedied with recovery sleep. It seems there is little that can be done if a memory is not encoded effectively in the first place,” according to Chee and co-authors.
As expected, vigilance was significantly impaired in the sleep-restricted group (p<0.001) as assessed 1 hour before the encoding session ─ with slower response speed (p<0.001) and greater sleepiness (p=0.001) compared with the controls ─ but all the measures were not significantly different between groups when taken 1 hour before the retrieval session.
“It appears that the impairment to subjective alertness and psychomotor vigilance associated with several nights of partial sleep restriction did not account for deficits to long-term memory encoding … suggesting a specific deficit in the ability to effectively encode new information following successive nights of sleep restriction,” said Chee and co-authors.
“The lapses in attention that go hand-in-hand with insufficient sleep are very likely to impact upon a student’s ability to learn, but here we show that even when stimuli appear to be attended to by sleep-restricted individuals, they are not encoded effectively,” they added.
Working memory and executive function were similar at baseline, and therefore unlikely to contribute to the differences in picture recognition between groups, according to the researchers.
“More emphasis must be placed upon proper sleep habits, and possible counter measures to poor sleep should be explored, for children to learn and retain information more effectively.”