Researchers induce sleep-like brain activity to reverse memory loss

By inducing specific patterns of activity in small portions of the brain in awake mice, researchers supported by the National Institutes of Health (NIH) have triggered a recalibration of neural connections that normally only occurs during sleep. This new approach offset the effects of sleep deprivation in memory tasks and revealed features of sleep that are key to its restorative effect.

What we're essentially doing is forcing sleep in a local region of the brain. While that part is solidifying memories and restoring learning capacity, other parts stay aware/vigilant and connected to environment. Dolphins do something similar, sleeping with only one brain hemisphere at a time."

Chiara Cirelli, M.D., Ph.D., corresponding author, professor of psychiatry, University of Wisconsin-Madison

Non-rapid eye movement (NREM) sleep, which makes up about 80% of sleep for adults, is when the junctions between neurons that make memories are evaluated. During this phase, the brain protects important connections for long-term storage, prunes those that are less necessary, and makes space for new ones.

Cirelli and her colleagues previously showed that, when sleep-deprived, both rats and humans can exhibit local slow-wave brain activity - a hallmark of NREM sleep - while awake. These deprivation-induced dips into sleep-like activity may have been too sporadic and brief to be beneficial, but the findings raised questions about the possible effects of a longer, more systematic version of this activity.

In the new research, the authors used a combination of light-pulsing implants and genetic modifications to induce rhythmic on-and-off activity in one side of the brains of sleep deprived mice for 30 minutes at a time, mimicking patterns that occur during NREM sleep.

When mice subsequently slept, slow-wave activity was lower in the specific brain regions the authors had stimulated, indicating less need for sleep. Additional experiments suggested that this effect hinged not on the overall reduction in neuronal firing, which some scientists had suggested was critical to recover from wake-induced neuronal fatigue, but rather on the specific alternating on-and-off pattern of activity.

The researchers explored potential benefits through a behavioral test of tactile memory, for which sleep is important. Sleep-deprived mice who received stimulation in motor and sensory regions on both sides of the brain performed similarly to those who were well rested. Sleep-deprived mice who did not receive stimulation performed significantly worse.

In future studies, Cirelli aims to learn whether similar effects could be replicated in humans using less invasive, transcranial stimulation technology.

"This research further decodes why we sleep and how we learn, which brings us a step closer to understanding how to better prevent and treat cognitive decline," said Amy Bany Adams, Ph.D., acting director of the NIH's National Institute of Neurological Disorders and Stroke (NINDS), which funded the research.