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Sleep Deprivation Affects our Ability to Recall Memories Under Stress.


We have known for quite some time now that sleep is essential to forming long-term memories. In fact, a recent study by researchers at Brandeis University found that without sleep, memorization during all-night study sessions was completely worthless. In a new study that sheds more light on the link between memory and sleep, researchers from Uppsala University in Sweden are finding that sleep is both essential to capturing long-term memories and accessing them under stress.

Publishing their findings in the journal SLEEP, Swedish researchers Jonathan Cedernaes and Christian Benedict explored the connection between the duration of sleep received each night, and the ability to recall long-term memories when there is a lot of pressure. In order to do this, researchers studied 15 participants, giving them 15 card pairings on a computer screen and asking them to memorize as many as they can. Half of the subjects were then given four hours of sleep, and the other half was given a sleep of eight hours.

When asked the following day to recall the 15 card pairings from the previous day, researchers observed no difference on the impact of sleep duration on the subject’s ability to remember; those who got four hours of sleep were able to recall the pairings just as well as those who got eight hours.

However, when researchers exposed their subjects to cognitive stress, a significant difference in memorization was observed. After being exposed to either four or eight hours of sleep, researchers subjected participants to 30 minutes of acute stress the morning after. For example, while asking participants to recall a newly learned list of words, they were exposed to loud noise. Under this sort of stress, those who only received 4 hours of sleep recalled significantly less, showing an overall reduction in their ability to access long-term memory by about 10 percent. Those who received eight hours did not show the same and recalled their memories with ease.

“On the basis of our study findings, we have two important take-home messages,” said Jonathan Cedernaes, of the Department of Neuroscience at Uppsala University. “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, which can possibly be detrimental in real- world scenarios. Second, interventions such as delaying school start times and greater use of flexible work schedules, that increase available snooze time for those who are on habitual short sleep, may improve their academic and occupational performance by ensuring optimal access to memories under stressful conditions.”

Throughout the school and work day we are presented with a variety of different stressful obstacles that impact our ability to process and recall information. When we lose sleep, this ability is further diminished, and we have an even more difficult time going through our day. Other studies have shown that the increased stress that often comes with lack of sleep can even lead to certain conditions associated with memory, like Alzheimer’s.

Researchers believe that in the near future it will be necessary to study how lack of sleep and stress lead to these sorts of conditions, and what should be done to prevent them from happening. “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,” Cedernaes said.

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Gene Therapy Restores Hearing In Mice

A new study has successfully restored hearing in mice that have a genetic form of deafness by utilizing gene therapy. Published in the journal, Science Translational Medicine, the study was a collaboration between Harvard Medical School, Boston Children’s Hospital and the École Polytechnique Federale in Switzerland. The new study may lead the way for gene therapy to be used on humans who suffer a genetic form of deafness.

According to the World Health Organization (WHO) an estimated 360 million people have a form of deafness, and more than 70 different genes are known to cause it. Prof. Jeffrey Holt of the Department of Otolaryngology, F.M. Neurobiology Centre at Boston and Harvard Medical School, worked with first-time author Charles Askew.

TMC1 was chosen as the specific gene to focus the study’s efforts on because it is a common case of genetic deafness, accounting for more than 8% of cases. The gene encodes a protein that plays a central part in hearing by helping to convert sound into electrical signals which then go to the brain.

Two types of mice were tested, one had the TMC1 gene removed – a good model for humans with TMC1 mutations, as children who have two TMC1 mutations often undergo hearing loss at a young age. The other mice carried a specific TMC1 gene mutation, known as Beethoven, which serves as a good model for TMC1 related deafness, where deafness occurs gradually between the ages of 10-15 years of age.

To deliver the healthy gene, scientists created an adeno-associated viral 1 (AAV1) together with a promoter, which serves as a genetic sequence that turns the gene on only in certain sensory cells of the inner ear known as hair cells.

Researchers screened several AAV1 serotypes and promoters to seek an efficient combination. They discovered one such combination was successful in restoring sensory transduction, auditory brainstem responses and acoustic startle reflexes in otherwise deaf mice.

The results proved to be outstanding. Scientists restored the ability of sensory hair cells to respond to sound enabling those mice carry the Beethoven gene to hear again. Hearing was tested by placing the mice in a “startle box” to measure the reactions of the mice. Prof. Holt explains: “Mice with TMC1 mutation will just sit there, but with gene therapy, they jump as high as normal mice.”

Mice that carried the TMC1 gene deleted also showed promise, with some hearing partially restored.