Summary: A new study replicated key restorative aspects of sleep in awake mice by recreating the brain’s slow-wave, “on-and-off” firing pattern in targeted, localized regions. Using optogenetic stimulation, researchers induced rhythmic neural alternations that mimic non-rapid eye movement (NREM) sleep for 30 minutes at a time. This localized intervention offset memory deficits caused by sleep deprivation and reduced the subsequent biological need for sleep in the stimulated areas, indicating that sleep’s restorative power depends on specific rhythmic patterns rather than a simple reduction in overall neuronal activity.
Key Facts
- Localized sleep induction: Scientists were able to force sleep-like neural dynamics in small, isolated brain regions while the rest of the brain remained awake and responsive to the environment.
- Optogenetics and genetics: The experiment combined genetic targeting with light-pulsing implants to produce rhythmic on/off neural activity in selected cortical areas for repeated 30-minute intervals.
- NREM pruning and memory consolidation: During NREM sleep, the brain reviews synaptic connections—safeguarding important links for long-term memory while pruning weaker ones to make room for new learning. The induced patterns replicated these core processes locally.
- Against simple neuronal fatigue models: The results show that a blanket reduction in firing is not sufficient for restoration. The alternating slow-wave pattern itself appears to be the critical trigger for the brain’s restorative and memory-preserving mechanisms.
- Reduced local sleep debt: After stimulation, slow-wave activity during subsequent sleep was significantly decreased in the targeted regions, indicating that local sleep requirements had been met by the intervention.
- Memory preservation: In tactile memory tasks dependent on sleep, sleep-deprived mice that received the localized stimulation performed similarly to fully rested controls; sleep-deprived mice without stimulation performed worse.
- Human translation potential: The study’s corresponding author, Dr. Chiara Cirelli, plans to investigate whether non-invasive transcranial stimulation can reproduce these localized restorative patterns in humans to help prevent cognitive decline.
Source: NIH
Overview
Researchers supported by the National Institutes of Health (NIH) demonstrated that inducing cortical ON/OFF periods in awake mice can reproduce essential sleep functions locally. By applying optogenetic stimulation to specific cortical areas, they recreated the rhythmic slow-wave activity characteristic of NREM sleep. The intervention recalibrated neural connections in those regions, offset memory impairment from sleep loss, and reduced the local need for sleep when the animals later slept.
“What we’re essentially doing is forcing sleep in a local region of the brain,” said Chiara Cirelli, M.D., Ph.D., professor of psychiatry at the University of Wisconsin–Madison. “While that part is consolidating memories and restoring learning capacity, other parts remain alert and connected to the environment.” She noted that some animals, such as dolphins, exhibit unihemispheric sleep, where one hemisphere rests while the other remains active.
In humans and rodents, NREM sleep—approximately 80% of adult sleep—is the phase when synaptic connections underlying memories are refined. Important connections are consolidated, weaker ones are pruned, and overall synaptic strength is adjusted to enable new learning. Earlier work by Cirelli and colleagues showed that brief, local slow-wave events can occur during wakefulness in sleep-deprived rats and humans, but these episodes were likely too brief to achieve substantial restorative benefit.
The current experiments used optogenetics to impose alternating on/off neural periods in one cortical hemisphere of sleep-deprived mice. These periods mimicked NREM slow waves for controlled 30-minute sessions. When the animals were subsequently allowed to sleep, slow-wave activity and synchrony were reduced specifically in the stimulated areas, consistent with a local reduction in sleep need. Crucially, additional tests showed that this effect depended on the precise rhythmic alternation of neural activity rather than simply lowering overall firing rates.
Behavioral testing focused on tactile memory, a system that depends strongly on sleep-dependent consolidation. Sleep-deprived mice that received bilateral stimulation over sensorimotor regions retained memory performance at levels comparable to rested controls. Sleep-deprived mice without stimulation displayed the expected impairments.
Cirelli and colleagues plan to explore whether non-invasive transcranial stimulation can reproduce these localized restorative effects in humans, with the long-term goal of protecting cognition and reducing the impact of sleep loss on memory and learning.
“This research further decodes why we sleep and how we learn, bringing us closer to approaches that might prevent or 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 study.
Key Questions Answered:
A: By targeting that region with genetic techniques and light pulses. Optogenetic stimulation forces a localized, rhythmic on/off firing pattern that mimics NREM slow waves in a small area while other brain regions remain awake and connected to sensory inputs—an effect analogous to unihemispheric sleep observed in some animals.
A: No. The study shows that a passive reduction in overall neuronal firing is not sufficient. Instead, the brain requires the alternating “on-and-off” slow-wave pattern to engage the mechanisms that restore synaptic balance and support memory consolidation.
A: This is an active area of research but not yet realized. The current results were achieved in mice with invasive implants. Researchers are planning human studies using less-invasive transcranial stimulation to test whether the same memory-preserving and restorative effects can be achieved safely.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional context was added by staff writers to clarify implications and next steps.
About this sleep and brain stimulation news
Author: Jonathan Griffin
Source: NIH
Contact: Jonathan Griffin – NIH
Image: Image credit: Neuroscience News
Original Research: Open access. “Induction of cortical ON/OFF periods in awake mice fulfills sleep functions” by Kort Driessen, Fabio Squarcio, Giulio Tononi & Chiara Cirelli. Nature Neuroscience. DOI: 10.1038/s41593-026-02318-9
Abstract
Induction of cortical ON/OFF periods in awake mice fulfills sleep functions
Slow-wave sleep in mammals is defined by synchronized neuronal activity that alternates between on and off periods. Slow-wave activity (SWA) and synchrony reflect sleep need, correlate with synaptic strength in cortical circuits, and promote synaptic downselection and memory consolidation. This study tested whether these core benefits of sleep can be produced during wakefulness.
Using optogenetics, the authors induced local alternating on/off periods during wakefulness in mice. This manipulation led to a local ipsilateral reduction in SWA and synchrony during subsequent sleep and decreased markers of synaptic strength. Bilateral induction of off periods over sensorimotor cortex during sleep deprivation restored memory consolidation.
These findings indicate that inducing on/off activity while awake can reduce local sleep need and accomplish essential functions of sleep.