## The Possibility of Reproducing Sleep Effects Without Closing Your Eyes

American neurobiologists conducted a study to find out whether it is possible to gain the benefits of sleep without actually entering a typical sleep state. Experiments on rodents showed that artificially creating alternating phases of neural activity and rest in the cortex of awake mice can trigger effects similar to those observed during slow-wave sleep. This approach also helped improve memory. Similar studies on humans are planned for the near future.

### The Role of Sleep in Brain Function

Sleep is essential not only for rest but also for restoring brain functions, memory, and restructuring synaptic connections. During sleep, the brain enters a special active mode, continuing to perform important tasks that are difficult to accomplish while awake. Throughout the day, new synapses—connections between neurons—are formed, helping to consolidate new information and acquired experiences.

During learning or memorization, the brain changes the strength and structure of synapses between neurons involved in these processes. Useful connections are strengthened, while rarely used ones weaken, allowing the brain to highlight important information and conserve resources. Sleep optimizes neural networks so that crucial connections are preserved and work more efficiently. This process of maintaining synaptic balance is known as the synaptic homeostasis hypothesis.

### The Slow-Wave Sleep Phase and Its Importance

It is believed that slow-wave sleep (NREM sleep), which begins immediately after falling asleep and makes up 75–80% of nightly rest, plays a key role in maintaining synaptic homeostasis. During this period, brain activity decreases and rapid eye movements are absent. The cerebral cortex displays characteristic activity: large groups of neurons periodically switch from an active state to an almost silent one and back again, repeating several times per second. These synchronized transitions are thought to help restore the brain after wakefulness and support the normal functioning of neural networks.

Similar mechanisms may be found in animals with unihemispheric sleep, such as dolphins, ducks, and fur seals, where one hemisphere of the brain is in NREM sleep while the other monitors the environment.

### The Mouse Experiment

In the experiment, researchers implanted a silicon probe into one hemisphere of the brains of genetically modified mice. This probe allowed them to simultaneously record and control neural activity using optogenetic light stimulation. A probe for standard activity recording was placed in the other hemisphere to compare results.

The mice were kept awake for five hours and given new objects to explore. To induce a sleep-like state in a small area of the cortex, two methods were used: activating inhibitory neurons, which caused rhythmic activity resembling the delta waves of slow sleep, and temporarily "switching off" excitatory neurons with light, leading to a sharp decrease in activity in the targeted brain region.

After this, the animals were allowed to sleep. Brain activity recordings showed that the stimulated area showed almost no signs of needing sleep, indicating partial restoration of function even during wakefulness.

### Impact on Memory

To test the effect of sleep-like activity on memory, an additional experiment was conducted using a novel texture recognition test. The mice were divided into three groups: one slept normally, the second was deprived of sleep, and the third experienced artificially induced sleep-like neural cycles while awake. The next day, researchers measured how much time the animals spent on the area with the new texture.

Mice deprived of sleep were worse at recognizing changes and showed little reaction to novelty, while those that slept or received artificial stimulation demonstrated normal behavior typical of memory recovery. The level of memory restoration in mice with artificial stimulation was comparable to that of animals that had a full night's sleep.

### Prospects for Human Application

Researchers plan to test this technology on humans using non-invasive transcranial electrical stimulation, which affects the brain through the scalp and does not require surgery. However, it is too early to talk about fully replacing sleep.

Modern science distinguishes two main phases of human sleep—NREM and REM sleep. The second phase is characterized by rapid eye movements. The reasons why alternating these phases ensures complete recovery of the body are not yet fully understood. The new experiment showed that some of the beneficial effects of sleep can be artificially reproduced, but sleep itself will likely remain an irreplaceable human need for a long time.

The scientific paper was published in the journal Nature Neuroscience.