Light Stimulation in Awake Mice Produced Deep-Sleep Memory Effects

Researchers at the University of Wisconsin-Madison used light to induce patterns of neuronal activity that normally occur only during deep sleep, and the treated mice retained memory performance after sleep deprivation. Chiara Cirelli led the team that genetically engineered mice so selected neurons could be switched off by light.

They implanted a light-sensitive probe into one hemisphere of each animal’s brain.

The mice were kept awake for five hours by exposure to novel objects. Near the end of this period the probe was switched on and off repeatedly for 30 minutes to reproduce the synchronized firing and silencing that defines NREM slow-wave activity. After the stimulation ended, the animals were allowed to sleep.

Brain recordings showed that the stimulated hemisphere did not display the elevated need for deep sleep that normally follows sleep deprivation. A separate experiment tested whether the same procedure preserved memory. Mice first explored a square box lined with identical carpet texture on both sides for 15 minutes.

They were then divided into three groups: undisturbed sleep, one hour of sleep deprivation, or one hour of sleep deprivation plus the artificial slow-wave stimulation. The next day the mice returned to the box, now with one side changed to a new carpet texture. Sleep-deprived animals without stimulation spent equal time on both textures, indicating they did not recognize the familiar side.

Both rested mice and sleep-deprived mice that received the stimulation spent more time exploring the novel texture. NREM sleep accounts for about 80 per cent of total sleep time in adults. 1038/s41593-026-02318-9.

Vladyslav Vyazovskiy of the University of Oxford, who was not involved in the work, said it should be possible, at least in theory, to replicate these results in humans. The researchers plan to test whether comparable effects can be produced non-invasively with transcranial electrical stimulation.