The Science of sleep: Why a good night's rest gets harder with age

It's well known that getting a good night's sleep becomes more difficult as we age, but the underlying biology for why this happens has remained poorly understood.

A team of  scientists has now identified how the brain circuitry involved in regulating sleepfulness and wakefulness degrades over time in mice, which they say paves the way for better medicines in humans.

Research has shown that sleep deprivation  is linked to an increased risk of multiple poor health outcomes, from hypertension to heart attacks, diabetes, depression and a build up of brain plaque linked to Alzheimer's.

Insomnia is often treated with a class of drugs known as hypnotics, which include Ambien, but these don't work very well in the elderly population.

Hypocretins are key brain chemicals that are generated only by a small cluster of neurons in the brain's hypothalamus, a region located between the eyes and ears.

Of the billions of neurons in the brain, only around 50,000 produce hypocretins. In 1998 scientists discovered that hypocretins transmit signals that play a vital role in stabilizing wakefulness. Since many species experience fragmented sleep as they grow old, it's hypothesized that the same mechanisms are at play across mammals, and prior research had shown degradation of hypocretins leads to narcolepsy in humans, dogs and mice.

Now it was  found  that the older mice had lost approximately 38 percent of hypocretins compared to younger mice. 

Researchers  also discovered that the hypocretins that remained in the older mice were more excitable and easily triggered, making the animals more prone to waking up.

This might be because of the deterioration over time of "potassium channels," which are biological on-off switches critical to the functions of many types of cells.

The neurons tend to be more active and fire more, and if they fire more, you wake up more frequently

Identifying the specific pathway responsible for sleep loss could lead to better drugs.

Shi-Bin Li et al, Hyperexcitable arousal circuits drive sleep instability during aging, Science (2022). DOI: 10.1126/science.abh3021