American scientists have found that the relationship between lack of sleep and increased susceptibility to pain is responsible not only for the somatosensory cortex but also for other areas such as the insula wolf and the nucleus accumbens that "decide" whether the stimulus causes pain or not . For this, the researchers conducted a functional magnetic resonance imaging experiment with people who spent the night in the laboratory. The article was published in The Journal of Neuroscience.
The relationship between lack of sleep and increased nociception has been demonstrated more than once by scientists: under laboratory conditions in humans and animals, susceptibility to the effects of pain stimuli increases with lack of sleep. However, brain regulation is poorly studied: in addition to the somatosensory parts of the brain responsible for processing the signals received by the skin receptors, other parts of the brain may also be sensitive to lack of sleep. . In addition, it is not known how changes in sleep affect the pain threshold of an individual.
The new experiment
This decided to find scientists under the leadership of Adam Krause of the California Institute of Technology in Berkeley who conducted two studies with people in the lab and an online survey. The first experiment was attended by 25 volunteers, each of whom spent two nights in the laboratory: one with eight hours of sleep and the second without sleep (the interval between two nights was at least one week).
The pain threshold of each participant was measured with heat: for this, a special heating device was placed on the skin of the left leg, whose temperature gradually increased by one degree. The participants of the experiment were asked to observe the moment when the pain of the effects of the temperature stimulus reached seven points on a ten-point scale.
In the morning after night in the laboratory, the participants' pain threshold was checked again. The scientists found that a night of insomnia significantly reduced participants' pain threshold: lack of sleep led to a lower temperature being considered unpleasant.
The brain was also observed
In addition, the scientists performed a functional MRI experiment to study brain activity when exposed to painful and neutral stimuli. As expected, the impact of high painful temperatures increased somatosensory cortex activity. A decrease in activity was observed in the thalamus and nucleus accumbens – the part of the brain that participates in the formation of the pain threshold (ie decides whether or not the pain is stimulated) – as well as in the insula lobe, whose damage leads to abnormalities in pain perception.
In an online survey of the effects of sleep deprivation on pain, 236 volunteers who reported experiencing pain of another nature (eg, chronic pain or pain after fractures) participated. Each participant underwent two surveys: in the morning, to report how much they slept well and at night to report the intensity of their feelings of pain during the day.
The authors concluded that lack of sleep reduces the pain threshold of people, which makes them more susceptible to nociceptive stimuli. The mechanism of this is not limited to hypersensitivity, as can be seen in somatosensory cortex activity, but it also extends to a kind of inhibition of those parts of the brain that decide whether the stimulus is physically unpleasant or not.
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