Ask any new mother what is most frustrating about the first few months of an infant’s life and you will probably get the same answer – the increased forgetfulness that comes with lack of sleep. Researchers have suspected for some time that sleep continuity affects memory and that when sleep is interrupted, even if total sleep hours is not affected, memory is impaired. A team of doctors at the University of Stanford have used a technology called optogenetics to target specific neurons in the brain and prove that a minimum amount of continuous sleep is crucial for memory consolidation.
Continuous Sleep is Critical for Preventing Memory Loss
Optogenetics uses light to control cells that have been genetically engineered to respond to light pulses. Dr. Luis de Lecea, an associate professor of psychiatry and behavioral sciences, used the technology on laboratory mice to target hypocretin/orexin neurons which are important for switching brain circuits between sleep and wake states. He describes the method as a “very fine, very subtle way of sleep fragmentation” without affecting overall amount or intensity. This also allows the researchers to study interrupted sleep independent of the increased stress that comes with full arousal after sleep.
After undergoing the sleep manipulation, the mice attempted to complete a task where they encountered two objects – one which was new to them and one that they had seen before. The rodents spent just as much time with a new object as the familiar one, suggesting that their memory had been affected and that they did not remember ever encountering either object. Control mice conversely spent more time exploring the new object.
While the authors cannot establish just how much uninterrupted sleep humans need from this study, they suggested that memory could remain unaffected if at least 62-73% of sleep was maintained as normal, continuous sleep. Medical conditions that affect sleep continuity include sleep apnea, where a person stops breathing and wakes up hundreds of times during the night, and alcoholism.
The Stanford team plans to do more research on sleep mechanisms that affect memory, says first author Dr. Asya Rolls, but optogenetics would not be able to be used on humans because it relies on genetic engineering to create the target cells.
"Optogenetic disruption of sleep continuity impairs memory consolidation."
Asya Rolls, Damien Colas, Antoine Adamantidis, Matt Carter, Tope Lanre-Amos, H. Craig Heller, and Luis de Lecea. PNAS, Published online before print July 25, 2011, doi: 10.1073/pnas.1015633108
Image Credit: Remara Photography (Krisztina Tordai)