Washington State University researchers
have determined that the timing of an animal's sleep can be just as important as how much sleep it gets.
Ilia Karatsoreos, an assistant professor in WSU's Department of Integrative Physiology and Neuroscience, shifted mice from their usual cycle of sleeping and waking. He found that, while they got enough sleep, it was of poorer quality. Additionally, the animals had a disrupted immune response, leaving them more vulnerable to illness.
Sleep research usually focuses on the effects of sleep deprivation or the overall amount of sleep an animal needs. This is called sleep's homeostatic process, driven by sleepiness or "sleep pressure."
The work by Karatsoreos and his colleagues, published in the journal Brain and Immunity, and reported in Bioscience Technology
, is a rare look into the circadian process, a brain-driven clock that controls the rhythms of various biological processes. Research into the system has significant implications for modern living, because "disruption of the circadian clock is nearly ubiquitous in our modern society" because of nighttime lighting, shift work, jet lag and even the blue-tinged light emitted by cell phones and tablets.
Sleep researchers usually have a hard time studying sleep deprivation and the circadian cycle separately, as a change in one usually affects the other. Karatsoreos and his colleagues made sure their model did not affect an animal's total sleep, giving them a unique look into the effects on the timing of the sleeping-waking cycle. They used mice whose body clocks run at about 24 hours and housed them in a shorter 20-hour day, forcing their biological clocks out of sync with the light-dark cycle. After four weeks, the researchers injected the mice with lipopolysaccharide, to make an animal sick without being contagious. The researchers observed that the disrupted animals had blunted immune responses in some cases or an overactive response in others, suggesting the altered circadian cycle made them potentially less able to fight illness and more likely to get sick.
According to Karatsoreos, "This represents a very clear dysregulation of the system. The system is not responding in the optimal manner. Over time this could have serious consequences for an organism's health. Just like you have a car that you're running into the ground: things don't work right, but you keep driving it until it stops. That's what could happen if you think of disruption going on for years for somebody who's working shift work."
Surprisingly, the mice on the 20-hour cycle were getting the same amount of sleep as they did on the 24-hour cycle, but the sleep was not as good. The mice awakened more frequently, and the pattern of electrical activity in their brains related to restorative sleep was greatly lowered.