Its always been a mystery why probably the most basic human experiencesfeeling physical painfluctuates in intensity during the day. Since the start of medicine, doctors and patients have pointed out that various kinds of pain have a tendency to get worse during the night. Most research up to now has tried to link mounting nighttime pain to sleep deprivation or disrupted sleep, but with limited success.
In a recently published study, scientists led by Claude Gronfier at the Lyon Neuroscience Research Centre in France have finally reveal changing pain sensitivity, suggesting our circadian clock strongly shapes these shifts, with a characteristic peak and trough of intensity at differing times of day.
Even individuals who cant dance have internal rhythms thrumming through every system within their body. Referred to as circadian rhythms, these biological processes tune their activity to go up and fall at precise times over the day, driven by the bodys internal clock. They influence almost every bodily system, exerting control over virtually all areas of our physiology and behavior, says Lance Kriegsfeld, a circadian biologist at the University of California, Berkeley.
The task by Gronfier and his team revealed the influence of the rhythms on pain by showing a short, painful heat stimulus was perceived to be most painful around 3 am and least painful at approximately 3 pm. Its very exciting, says Nader Ghasemlou, a pain scientist at Queens University in Kingston, Canada, who wasnt mixed up in research. It really is one of these brilliant studies that’s answering questions that weve had for a long period.
Uncertainties have persisted for such a long time because proving that anything is driven by the bodys internal clock is difficult and takes a grueling study design. Researchers must put participants in a controlled laboratory setting where they are able to eliminate any environmental or behavioral factors which could also result in a rhythmic fluctuation. This process is called a continuing routine protocol, where everything is kept constantlighting, temperature, usage of foodand its impossible to inform what time it really is. Participants must take a nap in a semi-recumbent position in a candlight room for at the very least 24 hours. Theyre prohibited to sleep, leave, or stand to utilize the toilet. Food is given only as small snacks every hour. Participants can speak to study associates, but staff are strictly forbidden from mentioning anything linked to the time. Beneath the protocol, nothing in the surroundings or the participants behavior is rhythmic anymore, Gronfier explains. So if the researchers spot a biological measure which has a 24-hour rhythm, that pattern hails from within, and precisely from the circadian timing system.
To discover pains rhythmic nature, Gronfiers team found 12 healthy teenagers who decided to undergo the protocol for 34 hours. Every two hours, the team tested their pain sensitivity utilizing a device positioned on the forearm that slowly increased in temperature by one degree Celsius until they reported pain. Participants usually stopped these devices before it reached around 46 degrees Celsius (115 degrees Fahrenheit). The participants were also tested with these devices set at specific temperatures (42, 44, and 46 degrees Celsius), and asked to rate on a visual scale the amount of pain they felt.