Sleeping uninterrupted for a certain duration may be necessary to retain new memories, scientists from Stanford University have discovered in a study in mice involving a new technique called optogenetics, which makes it possible to stimulate specific brain cells. The study was published in the Proceedings of the National Academy of Sciences today.
Many chronic conditions in which patients experience memory problems also involve sleep problems. For example, patients with Alzheimer disease, alcoholism, and sleep apnea all experience disruptions in the duration or quality of sleep. But teasing out the relationship between sleep disturbances and memory problems has been difficult. Previous attempts to simulate brief interruptions in sleep in animal models have involved physically handling the animals or other techniques that may not only interrupt sleep but also may reduce the total duration of sleep or cause stress to the animals—conditions that also might impair memory.
To avoid such problems, the researchers used optogenetics (a technique that allows specific cells to be controlled by light pulses) to briefly interrupt the animals’ sleep without interfering with their sleep in other ways. In the study, the investigators used mice that had been genetically engineered so that certain brain cells that play a role in switching between sleep and waking could be controlled by pulses of light. Using this technique, the scientists found that fragmented sleep reduced the ability of mice to remember objects they had seen the previous day.
According to a statement from coauthor H. Craig Heller, PhD, a professor of biology at Stanford, the findings, “point to a specific characteristic of sleep—continuity—as being critical for memory.”
The findings also suggest, the authors said, that disruptions in sleep alone may account for some of the memory problems associated with conditions such as Alzheimer or sleep apnea. They also suggest that optogenetics may be a useful technique for further probing the effects of sleep on memory.