Yawning more common in MS
A number of recent studies have looked at the phenomenon of yawning in a variety of neurological conditions, including multiple sclerosis.
People typically yawn about 28 times a day, most often just after waking up or just before going to sleep. Yawning is often accompanied by swallowing, either during the yawn or shortly afterward. In contrast, people with MS appear to yawn more often than non-MS individuals, and their yawns are less likely to be associated with spontaneous swallowing (Erkoyun and colleagues. Mult Scler Relat Disord 2017;17:179-183). The reasons for this, and for yawning itself, are complex and have been much-debated.
Yawning begins in the womb and continues throughout a person’s life. Why people yawn isn’t known, but there are many theories about it. The physiological hypotheses hold that yawning occurs because of a physical need (e.g. to increase the supply of oxygen, to re-regulate pressure in the ear). An example is fish, which yawn in response to low oxygen levels.
A more recent physiological theory is that people yawn to reduce body temperature (called thermoregulation), most notably in the brain. One experiment found that when a cold pack was applied to people’s heads, they were less susceptible to “contagious yawning” (i.e. yawning when they see someone else yawning).
“Contagious yawning” led to the social/communication hypothesis, which suggests that seeing someone yawn activates brain areas associated with imitation, empathy and social behavior (Guggisberg and colleagues. Neurosci Biobehav Rev 2010;34:1267-1276). One suggestion is that contagious yawning enables a group of animals to remain alert to danger, another that yawning enables an animal herd to synchronize sleeping and waking. “Contagious yawning” is usually confined to the same species, but studies have shown that a person yawning can make a dog (and sometimes a cat) yawn.
The idea that yawning can regulate brain temperature led to some investigations in MS, since an increased body temperature can worsen MS symptoms. One group of researchers found that about 1 in 3 people with MS reported that yawning improved their MS symptoms, and improvements typically lasted a few minutes after a yawn (Gallup and colleagues. Sleep Med 2010;11:329-330). Yawning may be because of elevated temperature, but is probably more likely to be due to MS fatigue and/or insomnia.
Another theory is that people yawn in order to switch from default mode to activated mode. The default mode network is a set of interconnected brain areas that show a high level of activity when the mind is not engaged, and a low level of activity when the mind is focused (Teive and colleagues. Arq Neuropsiquiatr 2018;76:473-480). As the default mode engages, the person gets sleepier. Yawning switches the person to alert mode, which helps the body clear itself of chemical messengers that promote sleep. In keeping with this theory, people with MS may be suffering from “default mode overload” because of MS fatigue and/or poor-quality sleep.
Yawning is controlled by the brain, and numerous studies have looked at the association between yawning and various neurological conditions. Yawning is rare in people with some neuropsychiatric conditions, such as schizophrenia and autism. Yawning is more common not just in MS but also in people with Parkinson’s disease (in part because the medications used promote yawning), just before the onset of a migraine, and after a stroke. One curious phenomenon is that in some people after a stroke, yawning can cause the paralysed arm to raise. This condition (called parakinesia brachialis oscitans) was parodied by one of Peter Sellers’ characters in the movie Dr. Strangelove.
Perhaps the hottest theory of yawning at the moment is the cortisol hypothesis. Cortisol is a hormone that is released during periods of stress, low blood sugar and fatigue, and helps to regulate the sleep-wake cycle. It has been suggested that yawning is a warning sign of elevated cortisol levels (Thompson and colleagues. Interact J Med Res 2012;1: e4, 1–9). As part of this theory, it’s believed that high cortisol levels are responsible both for yawning and fatigue in people with MS (Simon & Thompson. Med Hypotheses 2014;83:494-496). A recent study suggested that excessive yawning (usually defined as three yawns in a 15-minute period) may indicate elevated cortisol levels in people with MS (Thompson and colleagues. Mult Scler Relat Disord 2018l;23:51-55).
Interestingly, cortisol has effects on the immune system that may be beneficial in MS. It remains to be seen if excessive yawning (due to elevated cortisol levels) reduces the damage caused by inflammation during the long-term course of MS.
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