14 Jul Lack of Sleep May Impair Memory Functions In Stressful Situations
Medical Research: What is the background for this study? What are the main findings?
Dr. Cedernaes: Sleep is known to facilitate the formation of long-term memory in humans, by transferring newly learned memories from short-term to long-term memory stores. Studies however indicate that even shorter periods of sleep – including naps – can ensure access to different types of memories under normal restful conditions. Furthermore, while some studies have shown that acute sleep loss can exacerbate e.g. physiological responses to acute stress, it it has not been studied whether shortened sleep in combination with acute cognitive stress can have a negative impact on the retrieval of newly learned memories.
With this background in mind, we conducted a study where we aimed to investigate how nocturnal sleep duration impacts this memory transfer, and to what extent long-term memories formed by sleep remain accessible after acute cognitive stress.
We recruited 15 participants who in each of two sessions first underwent a learning session in the evening, during which they learned 15 card pair locations on a computer screen. Then, in one of the two experimental session, subjects slept for half a night (4-hr), instead being able to sleep for a full night (8-hr) in the other session. On the morning after each sleep condition, we had the subjects try to recall as many card pair locations as possible. We found that following half a night of sleep (4-hr), participants were equally able to recall memories for the learned card pair locations, as after a full night of sleep (8-hr). However, we also showed that the ability to retrieve memories following 30 minutes of acute stress, in the morning after these two sleep conditions, was different depending on whether the participants had slept for 8 or 4 hours. Following short sleep, the 30-min long stress exposure reduced the participants’ ability to recall the card pair locations that the participants had learned the previous night by around 10%. In contrast, no such stress-induced memory impairment was observed when the same men were allowed to sleep for a full night.
Medical Research: What should clinicians and patients take away from your report?
Dr. Cedernaes: On the basis of our study findings, we have two important take home messages:
First, even though losing half a night of sleep may not impair memory functions under baseline conditions, the addition of acute cognitive stress may be enough to lead to significant impairments. These impairments can possibly be detrimental in real-world scenarios, e.g. for medical health professionals who often have to go without sleep for long periods but also often face stressful situations in which they need to be able to access information stored in their long-term memory.
Second, interventions that allow people who usually don’t get enough sleep to sleep longer, including delaying school start times and greater use of flexible work schedules, may improve their academic and occupational performance by ensuring optimal access to memories under stressful conditions.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Cedernaes: An important next step will be to investigate how chronic sleep loss and/or more chronic stress may interact to impair the ability to retrieve memories that are consolidated during sleep. It will also be interesting to study how individual factors such as genetics may determine how vulnerable people are to the effects of acute or chronic stress when they have not slept enough.
Cedernaes et al. Short sleep makes declarative memories vulnerable to stress in humans. Sleep, 2015
Jonathan Cedernaes M.D., Ph.D. (2015). Lack of Sleep May Impair Memory Functions In Stressful Situations