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Are all evening-types doomed?

17 Jan

An interesting interview with Royette Tavernier of Wesleyan University, about her work on sleep and chronotype:

Empirical evidence indicates that US children and adults alike are getting less sleep than previous generations. This is a critical issue because of the importance of adequate and good-quality sleep for physical, cognitive, psychological, and interpersonal functioning. Furthermore, this pattern of increasing sleep debt coincides with increases in several physical and psychological health ailments, including depression, anxiety, and obesity.

Here is a paper she co-authored with the interesting title: “Are all evening-types doomed? Latent class analyses of perceived morningness–eveningness, sleep and psychosocial functioning among emerging adults”

“Aging impairs slow wave-spindle coupling, leading to overnight forgetting”

20 Dec

This story was covered on NPR, but they did not provide a link to the original paper. Unfortunately only the summary is available on line:

The coupled interaction between slow-wave oscillations and sleep spindles during non-rapid-eye-movement (NREM) sleep has been proposed to support memory consolidation. However, little evidence in humans supports this theory. Moreover, whether such dynamic coupling is impaired as a consequence of brain aging in later life, contributing to cognitive and memory decline, is unknown. Combining electroencephalography (EEG), structural MRI, and sleep-dependent memory assessment, we addressed these questions in cognitively normal young and older adults. Directional cross-frequency coupling analyses demonstrated that the slow wave governs a precise temporal coordination of sleep spindles, the quality of which predicts overnight memory retention. Moreover, selective atrophy within the medial frontal cortex in older adults predicted a temporal dispersion of this slow wave-spindle coupling, impairing overnight memory consolidation and leading to forgetting. Prefrontal-dependent deficits in the spatiotemporal coordination of NREM sleep oscillations therefore represent one pathway explaining age-related memory decline.




Autonomic nervous system activity and memory consolidation during sleep

18 Dec

According to a paper published in PNAS, “ autonomic nervous system (ANS) plays a role in associative memory consolidation during sleep.” Here is the abstract:

Throughout history, psychologists and philosophers have proposed that good sleep benefits memory, yet current studies focusing on the relationship between traditionally reported sleep features (e.g., minutes in sleep stages) and changes in memory performance show contradictory findings. This discrepancy suggests that there are events occurring during sleep that have not yet been considered. The autonomic nervous system (ANS) shows strong variation across sleep stages. Also, increases in ANS activity during waking, as measured by heart rate variability (HRV), have been correlated with memory improvement. However, the role of ANS in sleep-dependent memory consolidation has never been examined. Here, we examined whether changes in cardiac ANS activity (HRV) during a daytime nap were related to performance on two memory conditions (Primed and Repeated) and a nonmemory control condition on the Remote Associates Test. In line with prior studies, we found sleep-dependent improvement in the Primed condition compared with the Quiet Wake control condition. Using regression analyses, we compared the proportion of variance in performance associated with traditionally reported sleep features (model 1) vs. sleep features and HRV during sleep (model 2). For both the Primed and Repeated conditions, model 2 (sleep + HRV) predicted performance significantly better (73% and 58% of variance explained, respectively) compared with model 1 (sleep only, 46% and 26% of variance explained, respectively). These findings present the first evidence, to our knowledge, that ANS activity may be one potential mechanism driving sleep-dependent plasticity.

When I read this it occurred to me that there is evidence that older people experience higher levels of autonomic nervous system dysfunction and that this might be related to age related memory problems.

Sleep deprived judges hand out longer sentences

20 Feb

This study just appeared in the journal Psychological Science:

The degree of punishment assigned to criminals is of pivotal importance for the maintenance of social order and cooperation. Nonetheless, the amount of punishment assigned to transgressors can be affected by factors other than the content of the transgressions. We propose that sleep deprivation in judges increases the severity of their sentences. We took advantage of the natural quasi-manipulation of sleep deprivation during the shift to daylight saving time in the spring and analyzed archival data from judicial punishment handed out in the U.S. federal courts. The results supported our hypothesis: Judges doled out longer sentences when they were sleep deprived.

The Monday after the shift to day light savings time is associated with about 40 minutes of lost sleep. Other studies have found an increased number of car accidents on that day. The authors of this study report that sentences are 5% longer than those on comparison Mondays.

An interesting result, although I do have some skepticism about how well confounding variables can be controlled statistically.

13 Jan

An interesting paper about school schedules and student performance, published in The Review of Economics and Statistics, “How the Time of Day Affects Productivity: Evidence from School Schedules.” Here is the abstract:

Increasing the efficiency of the school system is a primary focus
of policymakers. I analyze how the time of day affects students’ productivity
and if efficiency gains can be obtained by rearranging the order of tasks they
perform throughout the school day. Using a panel data set of nearly 2 million
sixth- through eleventh-grade students in Los Angeles County, I perform
within-teacher, class type, and student estimation of the time-of-day effect
on students’ learning as measured by GPA and state test scores. I find that
given a school start time, students learn more in the morning than later in
the school day. Having a morning instead of afternoon math or English class
increases a student’s GPA by 0.072 (0.006) and 0.032 (0.006), respectively.
A morning math class increases state test scores by an amount equivalent
to increasing teacher quality by one-fourth standard deviation or half of the
gender gap. Rearranging school schedules can lead to increased academic

At first this would seem contrary to the evidence that suggests that later school start times seem to benefit students, but the author addresses this:

My study is also related to the school start time literature.
Research has indicated that due to changing sleep patterns
during adolescence, academic gains can be achieved by starting
school later. Carrel, Maghakian, and West (2011) use
random assignment of college classes and find that having one
hour earlier start times decreases students’ GPA by 0.031 to
0.076 standard deviations. Similarly, Dills and HernandezJulian
(2008) find that even when controlling for course
and student characteristics, students perform worse in earlier
classes. Edwards (2012) uses variation in school start times
produced by staggered busing schedules and finds that starting
school an hour later increases test scores by 2 percentage
Some have interpreted the finding that later school start
times increase students’ academic performance as implying
that given a school start time, students perform better
in the afternoon than in the morning (Carrel et al., 2011;
Dills & Hernandez-Julian, 2008). However, this hypothesis
has not been tested empirically. The common conclusion is
that later start times increase students’ achievement because
students are less sleep deprived. However, this says nothing
about how teaching and learning ability change throughout
the day. School start times affect the average learning in a day
but not differential learning throughout the day. Therefore,
the results of this paper and the school start time literature
estimate slightly different effects.

More evidence that sleep improves memory

26 Aug

From the journal Psychological Science:

“Both repeated practice and sleep improve long-term retention of information. The assumed common mechanism underlying these effects is memory reactivation, either on-line and effortful or off-line and effortless. In the study reported here, we investigated whether sleep-dependent memory consolidation could help to save practice time during relearning. During two sessions occurring 12 hr apart, 40 participants practiced foreign vocabulary until they reached a perfect level of performance. Half of them learned in the morning and relearned in the evening of a single day. The other half learned in the evening of one day, slept, and then relearned in the morning of the next day. Their retention was assessed 1 week later and 6 months later. We found that interleaving sleep between learning sessions not only reduced the amount of practice needed by half but also ensured much better long-term retention. Sleeping after learning is definitely a good strategy, but sleeping between two learning sessions is a better strategy.”



Some skepticism on sleep claims

22 Jan

From the good folks at Ask For Evidence.

‘The NHS Choices website claimed that “People who sleep less than seven hours a day are 30% more likely to be obese than those who get nine hours or more of sleep”. This seemed a little suspect as no data were provided to back up this claim, so I contacted NHS Choices to ask for evidence.’


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