Manipulating brain activity during deep sleep affects memory

Japanese researchers have found that manipulating a brain circuit that governs how certain memories are consolidated during sleep can prevent or enhance memory retention.

Experimentally manipulating the identified neural connection during non-REM sleep (deep sleep) can prevent or enhance memory retention in mice, showed the findings published in the journal Science.

Researchers at the RIKEN Brain Science Institute in Japan studied the long-known phenomenon of memory consolidation during sleep by building off their recent study on tactile perception in which they found that perceiving texture requires signalling within a neural circuit from higher-level motor-related brain regions back to lower-level touch-related sensory areas.

They reasoned that the same "top-down" pathway might also consolidate memories of textures.

"There is a long standing hypothesis that top-down input is crucial for memory consolidation and that during sleep, neurons in sensory regions activated during the initial experience can "reactivate" by unknown pathways," said lead researcher Masanori Murayama.

"We found such reactivation of the top-down pathway is critical for mice to encode memories of their tactile experiences," Murayama noted.

The researchers developed a task to assess memory retention that relies on the natural inclination of mice to spend more time investigating new items in their environment.

First they allowed mice to explore objects in two rooms with smooth floors, then they changed one of the smooth floors to a textured floor and again allowed the mice to explore.

With normal sleep, mice spent more time exploring the room with the textured floor, showing that they remembered the smooth room and were less interested in it.

To examine whether the top down circuit was responsible for memory consolidation during sleep, they manipulated the mice in several ways.

First, they showed that sleep deprivation immediately following the first tactile experience caused mice to explore the textured room less often on the second exploration, indicating that they did not remember the smooth room.

Next, they inactivated the neural pathway during deep sleep shortly after the first exploration and found that during the second exploration, mice performed as if they had been sleep deprived.

"Our findings on sleep deprivation are particularly interesting from a clinical perspective," Murayama said.

"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," Murayama noted.