Scientists can now trick mice brains into thinking they are sleeping, a breakthrough that may one day offer a new way to offset the effects of sleep deprivation in humans. Researchers at the University of Wisconsin-Madison, funded by the National Institutes of Health, have shown that by delivering targeted pulses of light to specific brain regions, they can mimic the restorative processes that normally only occur during deep sleep.
The experiment involved implanting tiny fibre-optic cables into the brains of mice that had been kept awake to ensure they were significantly sleep-deprived. Over the course of 30 minutes, the cables emitted pulses of light that recreated the rhythm of deep sleep within a localised area of the brain. “What we’re essentially doing is forcing sleep in a local region of the brain,” explained Dr Chiara Cirelli, a professor of psychiatry at the University of Wisconsin-Madison. “While that part is solidifying memories and restoring learning capacity, other parts stay aware and vigilant and connected to the environment.”
How the experiment works
The technique, known as optogenetic stimulation, allows scientists to control the activity of specific neurons with light. In this case, the pulses of light were tuned to mimic the slow oscillations that characterise deep, non-rapid eye movement (NREM) sleep. The stimulated region – part of the cortex – was effectively put into a sleep-like state while the rest of the brain remained awake. Dr Cirelli noted that dolphins do something similar naturally, sleeping with only one brain hemisphere at a time, a survival mechanism that allows them to remain vigilant while still getting rest. Unlike humans, whose breathing is automatic during sleep, dolphins must consciously control their breathing, making unihemispheric sleep essential.
After the stimulation, the mice showed signs of needing less sleep overall. When they eventually did sleep, the brain regions that had been stimulated displayed lower slow-wave activity – the electrical pulses produced by brain cells as the organ works to restore itself. This indicated that the local “sleep debt” in those areas had been partially fulfilled. The finding aligns with the synaptic homeostasis hypothesis, which proposes that during wakefulness, synaptic connections between neurons strengthen and multiply. Sleep, according to this theory, is essential for renormalising these connections, pruning weaker ones and restoring baseline balance. Recent human studies using PET scans have provided direct evidence for this, showing increased synaptic density markers in the brains of sleep-deprived individuals.
Memory test results
To test whether the induced sleep-like state actually provided cognitive benefits, the researchers ran a memory test. Mice that were sleep-deprived and had received the stimulation on both sides of their brain performed similarly to well-rested mice. In contrast, sleep-deprived mice that did not receive the stimulation performed “significantly worse”, the National Institutes of Health said. The results suggest that the localised brain stimulation was sufficient to consolidate memories and restore learning capacity, despite the animals being otherwise sleep-deprived.
Implications for humans
The technique has not yet been tested in humans, but the researchers point out that both humans and rats show signs of deep sleep slow brain waves while awake, suggesting that a similar approach might one day be feasible. Future studies will aim to determine whether similar effects can be reproduced in people using less invasive technology. Some research has already shown that targeted deep-brain stimulation during specific sleep cycles, delivered via a “closed-loop” system, can improve memory consolidation in humans and has shown promise for patients with memory disorders such as Alzheimer’s disease.
The potential significance of the work extends beyond laboratory curiosity. Most U.S. adults are not getting the seven to nine hours of sleep federally recommended for optimal health. According to the American Academy of Sleep Medicine, an estimated 25 to 30 million Americans have insomnia. Insomnia can be triggered by stress, but chronic insomnia may be related to long-term health conditions such as breathing, gastrointestinal or neurological disorders, UCLA Health says. Over time, lack of sleep raises the risk of heart disease, high blood pressure and Type 2 diabetes, according to the U.S. Centers for Disease Control and Prevention.
Amy Bany Adams, acting director of the NIH’s National Institute of Neurological Disorders and Stroke, said in a statement: “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.” The NIH funded the research. Separately, other work has explored techniques such as “cognitive shuffling” to help people fall asleep faster by generating random, emotionally neutral images that mimic the brain’s natural drift into sleep – but the Wisconsin study represents a more direct manipulation of the sleep machinery itself. For now, the results remain confined to mice, but they offer a tantalising glimpse of a future in which the brain could be tricked into thinking it has rested, even when it has not.