New research from a group at Stanford University has found that broken or interrupted sleep has a negative effect on the ability to build memories in mice. The research, published in the Proceedings of the National Academy of Science, shows that disrupting the sleep of mice made it harder for them to recognize and identify objects that should have been familiar to them. To study the mice, the researchers interrupted their sleep but made sure that the amount of time sleeping was no shorter than normal.
Using optogenetics, a technique where certain cells are genetically engineered to be controlled by light, the researchers targeted cells in the brain. The cells on which the researchers focused plays a critical role in switching the brain between the sleep and awake states. Light pulses were sent into the brains of the mice while they slept, to disrupt their sleep but not change their total sleep time or the quality or intensity of their sleep. The researchers then tested the mice memory by putting them in front of two objects, one new and one familiar. Mice whose sleep had been disrupted did not recognize either object, while mice who had slept undisturbed focused all their attention on the new object.
Sleep experts say that during the brain’s deep sleep state the brain is active, going through the day’s events and deciding what memories to hold onto. This is why interrupting sleep can cause memory problems. According to the researchers, a better understanding of the relationship between sleep and the effects on the brain could lead to new insights into conditions where memory loss is a symptom like Alzheimer’s, sleep apnoea, or alcohol addiction.
The researchers are quick to explain that a link between sleep disruption and memory loss in mice by no means provides an explanation for the cause of memory loss with conditions like Alzheimer’s. More research is still needed to further explore the sleep-memory relationship, but the researchers are confident that regardless of the total amount of sleep or the intensity of the sleep there is a minimal unit of uninterrupted sleep needed for memory consolidation.