Although we know which brain regions are activated during REM sleep, little is still known about the purpose of this activity. Researchers at the University of Bern and the Insel Hospital have discovered that the activation of neurons in the hypothalamus during REM sleep regulates eating behavior: when this activity is suppressed in mice, appetite decreases.

How REM Sleep Affects Food Intake

While we sleep, we cycle between different sleep stages, each contributing in a different way to making us feel rested. During REM (rapid eye movement) sleep, a special stage of sleep also known as paradoxical sleep when most dreams occur, certain brain circuits show very high electrical activity, although the function of this sleep-related activity is still unclear. REM sleep is a unique sleep phase in mammals that is closely associated with dreaming and is characterized by random eye movements and almost complete paralysis of the body.

The brain regions that show strong activation during REM sleep include, for example, areas that regulate memory functions or emotions. The lateral hypothalamus, a tiny, evolutionarily well-preserved brain structure in all mammals, also shows high activity during REM sleep. In waking animals, neurons from this brain region coordinate appetite and food consumption and are involved in the regulation of motivated behavior and addiction.

In a study, researchers led by Prof. Dr. Antoine Adamantidis at the University of Bern set out to investigate the function of hypothalamic neurons in mice during REM sleep. They wanted to better understand how neuronal activation during REM sleep influences our daily behavior. They discovered that suppressing the activity of these neurons reduces the amount of food the mice consume. According to the researchers, this suggests that REM sleep is necessary to stabilize food intake. The results of this study were published in the journal Proceedings of the National Academy of Sciences (PNAS).

Long-Lasting Effect on Neuronal Activity and Feeding Behavior

The researchers discovered that certain patterns of activity in lateral hypothalamic neurons, which normally signal feeding in the awake mouse, are also present when the animals are in REM sleep. To explore the significance of these activity patterns during REM sleep, the research group used a technique called optogenetics, in which they used light pulses to precisely turn off the activity of hypothalamic neurons during REM sleep. As a result, the researchers found that the activity patterns for food intake were altered and the animals ate less food.

They were surprised by the strength and persistence of our intervention on neuronal activity in the lateral hypothalamus and the behavior of the mice. The change in activity patterns was still measurable after four days of regular sleep. These results suggest that the electrical activity in hypothalamic circuits during REM sleep is highly plastic and essential for maintaining stable feeding behavior in mammals.

The results make it clear that not only the amount of sleep is necessary for our well-being, but that sleep quality plays an important role, especially in maintaining appropriate eating behavior. This is particularly important in our society, where not only the amount of sleep is decreasing, but also sleep quality is dramatically affected by shift work, nighttime screen use, or social jet lag in adolescents. The discovered link between the activity of neurons during REM sleep and eating behavior could help in the development of new therapeutic approaches to treat eating disorders. It could also be relevant for motivation and addiction.

How REM Sleep Loss Promotes Cravings for Sweets

It is not well understood how a lack of sleep affects areas of the brain that control cravings for unhealthy foods. A paper published in the journal eLife found that REM sleep loss led to increased consumption of unhealthy foods, particularly sucrose and fat. Researchers at the International Institute for Integrative Sleep Medicine (IIIS) at the University of Tsukuba used a method to induce REM sleep loss in mice, as well as a chemical-genetic technique to block prefrontal cortex neurons and the behaviors they mediate. As a result, the IIIS researchers found that inhibiting these neurons reversed the effect of REM sleep loss on sucrose consumption, while having no effect on fat consumption.

The prefrontal cortex plays a role in evaluating the palatability of food based on taste, smell, and texture. Furthermore, obese individuals tend to have increased prefrontal cortex activity when consuming high-calorie foods. The results suggest that the medial prefrontal cortex may play a direct role in controlling our cravings for weight-gain foods high in sucrose when we haven’t had enough sleep.