While you were sleeping, your muscles knit themselves back together and your metabolism whirred along. Now, researchers from California are exploring the system behind sleep and human growth hormone — two factors responsible for some of slumber’s most important benefits.
The study looked at how mouse brains reacted to light stimulation. These mammals tend to sleep only a little bit at a time, helping researchers better observe changes in their growth hormone activity through different sleep and wake cycles. Growth hormones juggle a myriad of responsibilities, including muscle and bone construction and fat burning.
Research has previously shown these levels peak during sleep. Thanks to circuity tracing techniques, the team pinpointed how, exactly, the brain coordinates this process.
It starts with a feedback loop that toes the line between wakefulness and sleep. As the growth hormone increases during the latter, it triggers the locus coeruleus [sih-roo-lee-us], an area of the brainstem that encourages alertness. When this activity reaches a breaking point — or should we say waking point — the locus coeruleus begins encouraging drowsiness instead.
In short: Sleep is the driver of growth hormone release, and this hormone, in turn, regulates wakefulness. Getting too little sleep lowers growth hormone levels, but too much of it shifts the brain toward wakefulness. A balance between the two keeps muscle growth and metabolic health in check, and the locus coeruleus’s part points to the possibility of the circuit affecting cognitive functions like attention.
Who are we to argue with another reason to hit the hay?