Memories “lost” due to sleep deprivation may still be there and a medication could help to recall them, according to a new study in mice. The human-approved asthma drug roflumilast was able to help mice recall memories that they previously were unable to grasp after sleep deprivation, which could be of huge use to people with amnesia and other sleep-related disorders.
We’ve all been there – the exam is coming up and you’re woefully underprepared, and you now have to make the fateful decision between cramming overnight and rocking up with your eyes half closed or getting a good night’s sleep and hoping the revision you did is sufficient. I personally chose a harsh version of both, in which I ended up sleep deprived but unable to remember the information I crammed in the night before.
Previously, scientists just assumed these memories were lost, with sleep deprivation preventing the brain from committing the information to memory. However, new research suggests that they may still exist within the brain, but something is stopping us from accessing them.
"Sleep deprivation undermines memory processes, but every student knows that an answer that eluded them during the exam might pop up hours afterwards. In that case, the information was, in fact, stored in the brain, but just difficult to retrieve,” said study author and University of Groningen neuroscientist Robbert Havekes in a statement.
To understand whether the problem lies in the creation or recall of memories made during sleep-deprivation episodes, scientists turned to optogenetics. By causing a light-sensitive protein to be produced in specific neurons that are activated during learning, the researchers were then able to use light to see exactly what was going on in the cells.
The mice were given a task in which they had to learn individual locations of objects and then recall the location of them after they had been moved a few days later. In mice that were sleep-deprived, they failed to recall the locations, but when the researchers activated neurons involved in memory recall, the mice were then able to identify the locations once more.
"However, when we reintroduced them to the task after reactivating the hippocampal neurons that initially stored this information with light, they did successfully remember the original locations," continued Havekes.
"This shows that the information was stored in the hippocampus during sleep deprivation, but couldn't be retrieved without the stimulation."
The researchers then gave the mice the drug roflumilast, which is approved for use in humans, in an attempt to mimic the activation of memory neurons. These mice recalled the locations of the objects, just as before, suggesting a possible avenue of use for retrieving “lost” memories with this drug. Further trials will be necessary, including possible human trials, but it highlights the possibility that memories are actually made in sleep-deprived periods, though they are inaccessible for some reason.
"It might be possible to stimulate the memory accessibility in people with age-induced memory problems or early-stage Alzheimer's disease with roflumilast," said Havekes.
"And maybe we could reactivate specific memories to make them permanently retrievable again, as we successfully did in mice."
The research was published in Current Biology.