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Memories “Lost” During Sleep Deprivation Can Be Recalled

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New research from the University of Groningen, published in Current Biology, has illustrated that memories made while sleep-deprived aren’t lost for good, they’re just more difficult to recall.

The effect of sleep deprivation on memory

Researchers know that sleep deprivation is bad for your memory, but whether sleep-deprivation-related amnesia is a result of direct memory loss or difficulty with memory recall was previously unknown.

Sleep and memory how are they linked?

Researchers hypothesize that memory consolidation the process by which key memories are preserved and excessive, unimportant memories are discarded happens as we sleep. When sleep-deprived, memories aren’t firmly consolidated, which can affect how accessible they are (i.e., how easily they can be recalled or whether they become “lost”).

Professor Dr. Robbert Havekes, associate professor in the neuroscience of memory and sleep, and team have identified that memories lost during sleep-deprived learning can be made accessible, using either optogenetic approaches or roflumilast, a drug used to treat asthma and chronic obstructive pulmonary disease.

What is optogenetics?

Optogenetics is a technique used in neuroscience to control neurons, using a combination of genetic engineering and light.

As an optogenetic approach to reactivating memories, the researchers engineered a light-sensitive protein to be selectively expressed in the neurons activated during learning. This allows recall of the learning experience when light is applied to those cells.

Sleep-deprived and well-rested mice performed a spatial learning task, in which they had to learn the locations of several objects. A few days later, the task was repeated, but with one object moved to a new location. The sleep-deprived mice were unable to detect the change, implying they could not recall the information learned in the first task.

The researchers then applied light to the neurons activated during the learning experience, and the sleep-deprived mice were able to recall the original locations of the objects. This indicates that the memories made while sleep-deprived aren’t lost forever, but they require stimulation to be recalled.

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Roflumilast targets the same molecular pathway as is activated during memory reactivation. “When we gave mice that were trained while being sleep deprived roflumilast just before the second test, they remembered, exactly as happened with the direct stimulation of the neurons,” explains Havekes.

This calls into question whether memories previously considered “lost”, such as in conditions including Alzheimer’s disease, could be reactivated in a similar way to make them permanently accessible.

Havekes aims to continue unraveling the molecular mechanisms of memory processing, asking: “What makes memories accessible or inaccessible? How does roflumilast restore access to these ‘hidden’ memories?”

This article is a rework of a press release issued by the University of Groningen. Material has been edited for length and content.

Reference: Bolsius YG, Heckman PRA, Paraciani C, et al. Recovering object-location memories after sleep deprivation-induced amnesia. Curr Biol. 2022. doi: 10.1016/j.cub.2022.12.006