While we are asleep, we transition between different phases of sleep, each of which may contribute differently to us feeling rested in the morning. During rapid eye movement (REM) sleep, a specific sleeping phase during which we dream intensely, various areas of the brain and brain circuits are highly active. So far, however, the purpose of this electrical activity remains unclear.
Among the brain regions that show strong activation during REM sleep are areas that regulate memory functions and emotions, for instance. The lateral hypothalamus, a tiny, evolutionarily well conserved brain structure in the diencephalon of all mammals, also shows high activity during REM sleep. When animals are awake, neurons from this brain region orchestrate appetite and the consumption of food, and they are involved in the regulation of motivated behaviors and addiction.
Researchers headed by Prof. Dr. Antoine Adamantidis at the University of Bern and Bern University Hospital set out to investigate the function of the activity of hypothalamic neurons in mice during REM sleep. They aimed at better understanding how neural activation in the hypothalamus during REM sleep influences our day-to-day behavior. They discovered that suppressing the activity of these neurons decreases the amount of food mice consume. “This suggests that REM sleep is necessary to stabilize food intake,” says Adamantidis.
Long-lasting effect
The researchers discovered that specific activity patterns of the cells in the lateral hypothalamus, which usually signal eating when the animals are awake, are also present in the stage of REM sleep. To assess the importance of these activity patterns during REM sleep they used a technique called optogenetics, with which they used light pulses to precisely shut down the activity of nerve cells during REM sleep. As a result, the researchers found that, in the case of mice that are awake, cell activity patterns for eating were modified and that the animals consumed less food.
“We were surprised how strongly and persistently our intervention affected the neural activity in the lateral hypothalamus and the behavior of the mice,” says Lukas Oesch, the first author of the study. He adds: “The modification in the activity patterns was still measurable after four days of regular sleep.” These findings suggest that electrical activity in hypothalamic circuits can be changed and lead to a stable eating pattern.
A question of quality
These findings indicate that sleep quantity alone is not solely required for our well-being, but that sleep quality also plays a major role. The researchers highlight how important high-quality sleep is for our eating behavior. “This is of particular relevance in our society where not only the sleep quantity is decreasing but where sleep quality is dramatically affected by shift work, late night screen exposure and social jet-lag in adolescents,” explains Adamantidis.
The discovered link between cell activity during REM sleep and eating behavior may help in developing new therapeutical approaches for treating eating disorders. They might also be relevant for motivation and addiction. “However, this relationship might depend on the precise circuitry, the sleep stage and other factors yet to be uncovered,” adds Adamantidis.
