31 May Deep sleep and memory
Each day we are bombarded with hundreds of pieces of new information. A good night’s sleep improves our ability to remember some of the more important details that run through our brain each day. Researchers at the RIKEN Brain Science Institute in Japan have discovered a brain circuit that governs how certain memories are consolidated during non-REM (deep) sleep. Published in Science magazine, the study shows how experimentally manipulating this circuit during deep sleep can prevent or enhance memory retention in mice.
The researchers assessed memory retention through their inquisitive nature. They allowed the mice to explore objects in two rooms with smooth floors, then changed one of the floors to a textured surface. With normal sleep, mice spent more time exploring the room with the textured floor, indicating they remembered the smooth room and were less interested in it. Typically, this behaviour was observed as long as the second exploration occurred within two days.
The importance this circuit activation in non-REM sleep suggests that memory consolidation might involve synchronous slow wave brain activity between the two brain regions that is characteristic of non-REM sleep. To test this, they artificially applied synchronous or asynchronous activity in the higher and lower regions of the circuit during non-REM sleep after the first tactile experience. Mice with asynchronous activation were unable to consolidate memories, but synchronous activation allowed them to retain a memory of the smooth floor for at least 4 days or twice as long as normal. The synchronous treatment even rescued the typical lack of memory retention in sleep-deprived mice.
“Our findings on sleep deprivation are particularly interesting from a clinical perspective,” says the lead researcher, Murayama. “Patients who suffer from sleep disorders often have impaired memory functions. Our findings suggest a route to therapy using transcortical magnetic or direct-current stimulation to top down cortical pathways to reactivate sleep-deprived neurons during non-REM sleep. Their next goal is to test this hypothesis in mouse models of sleep-disorders.