YAWNING

A yawn consists of a stereotyped behavioural pattern that begins with an inspiration associated with marked dilatation of the pharynx. At the peak of inspiration there are associated facial movements and the final part of yawning is passive rapid expiration. During yawning a coordinated sequence of events takes place involving facial, oropharyngeal, tongue, and respiratory muscles, associated with activity in the axial extensor and limb extensor muscles and with autonomic changes characterised by an increased parasympathetic outflow.

Yawning occurs preferentially in conditions of low vigilance (brain stem) and causes transient increases in arousal (brain stem) as indicated by EEG desynchronisation. Patients with brain stem ischaemic stroke present excessive yawning.

The neural structures that control yawning are presumably located in the brain stem near to or within other respiratory and vasomotor centres, especially those that control facial mimicry, mastication, throat movements, respiration, and possibly stretching.

Yawning also involves the hypothalamus and the midbrain as well as the reticular formation of the pons and medulla (brain stem)

excerpts from
Pathological yawning as a presenting symptom of brain stem ischaemia in two patients
L Cattaneo, L Cucurachi, E Chierici, and G Pavesi
J Neurol Neurosurg Psychiatry. 2006 January; 77(1): 98–100

***


•Yawning is considered to be contagious only in humans by some authors (Lehmann 1979; Walusinski 2004), but this view was recently challenged by a study on chimpanzees (Anderson et al. 2004). The latter study used an experimental video-based approach similar to that used for studying contagious yawning in humans (e.g. Provine 1986; Platek et al. 2003).
•The reported contagion effect in 33% of adult chimpanzees compares with 45–60% typically reported for humans.
•Human mirror neuron system is not involve in contagious yawning, which suggests that yawning is not a truly imitative act (Schürmann et al. 2005).
•Since there is convincing evidence for both self-recognition and empathy in chimpanzees but not in monkeys (De Waal 1996; Anderson & Gallup 1999), it may be predicted that, unlike chimpanzees and humans, monkeys do not show contagious yawning.

Excerpts from
Video-induced yawning in stumptail macaques (Macaca arctoides)
Annika Paukner* and James R Anderson
Biol Lett. 2006 March 22; 2(1): 36–38.


***


Using human college-age subjects, the present study tested the hypothesis that yawning is facilitated by higher than normal levels of CO2 or lower than normal levels of O2 in the blood

If yawning is a response to heightened blood CO2, the CO2 mixtures (3-5 %) should increase yawning rate and/or duration. If low blood O2 produced yawning, breathing 100% O2 should inhibit yawning.

The CO2/O2 hypothesis was rejected by the results of this research because breathing neither pure O2 nor gases high in CO2 had a significant effect on yawning although both increased breathing rate.
A second study found that exercise sufficient to double breathing rate had no effect on yawning.

The two studies suggest that yawning does not serve a primary respiratory function and that yawning and breathing are triggered by different internal states and are controlled by separate mechanisms.

Behav Neural Biol. 1987 Nov;48(3):382-93.

Yawning: no effect of 3-5% CO2, 100% O2, and exercise.

Provine RR, Tate BC, Geldmacher LL.

Department of Psychology, University of Maryland Baltimore County, Catonsville

***

Research shows that 11-week-old fetuses yawn.
The average yawn lasts about six seconds.
Your heart rate can rise as much as 30 percent during a yawn.
55 percent of people will yawn within five minutes of seeing someone else yawn.
Blind people yawn more after hearing an audio tape of people yawning.
Reading about yawning will make you yawn.
Olympic athletes before competition, paratroopers before the jump, often yawn .

***

Contagious yawning (yawning triggered by perceiving others’ yawning)

•a well-documented phenomenon
•widespread among vertebrate species
•children older than 4 years show contagious yawning.
•little is known about the mechanism
•some claim that it is based on the capacity for empathy Preston & de Waal 2002; Platek et al. 2003)
•susceptibility to yawn in response to others are related to the activity of the superior temporal sulcus and periamygdalar regions.
•structural abnormalities of these regions are reported in Autism Spectrum Disorder.
•Individuals with ASD are known to fixate more to the mouth than to the eyes when watching dynamic facial stimuli
•the perception of the eye region, not the mouth region, of yawning people is a potent stimulus for yawn contagion
Excerpts from

Absence of contagious yawning in children with autism spectrum disorder
Atsushi Senju, Makiko Maeda, Yukiko Kikuchi, Toshikazu Hasegawa, Yoshikuni Tojo, and Hiroo Osanai
Biol Lett. 2007 December 22; 3(6): 706–708.


***


Yawning is a stereotyped behaviour present in most mammals from rodents to humans and has been described since antiquity. Hippocrates considered yawning to be an exhaustion of the fumes preceding fever. Modern medicine did not pay much attention to it until the 1980s, when, with advances in neuropharmacology, yawning proved to be a valuable tool for the assessing dopaminergic activity and the pharmacological properties of new drugs. However, its precise role in human physiology is still unknown and its mechanisms remain unclear. The paper by Cattaneo et al (see pages 98–100) reports two cases of pathological yawning as the earliest symptom of brain stem infarction which introduces new arguments for locating this neuronal network in the lower brain stem.

Yawning occurs after waking up, before eating, before sleeping, and in passive activities when it is necessary to maintain a certain level of vigilance.It is then followed by an acceleration of the electroencephalographic rhythms. It does not serve a primary respiratory function and it clearly has a non‐verbal communicative status. Nevertheless, it is also a clinical sign in intracranial hypertension, migraine, or iatrogenic side effects of dopaminergic drugs and serotonin reuptake inhibitors. In basal ganglia disorders, yawning is reduced in patients with Parkinson's disease, and occurs more often in patients with Huntington's disease and supranuclear palsy than in controls. In healthy volunteers, apomorphine induces yawning which is also observed at the beginning of the “on” periods in Parkinson's disease.

The anatomical structures known to be implicated in the occurrence and control of yawning are the paraventricular nucleus of the hypothalamus (PVN), the hippocampus, the reticular formation, the neostriatum, and the cranial (V, VII, IX, X, XI, XII), cervical (C1–C4), and dorsal nerves. Yawning is probably a reflex answer of the brain stem reticular formation aimed to increase the cortical level of vigilance. Dopamine and oxytocin are the main neurotransmitters implicated in its modulation. Indeed yawning induces sensory efferents from the terminals of the fifth facial nerve to the reticular formation or the PVN through the spinothalamic and hypothalamic tracts. Stimulation of the dopamine D2 receptors of the PVN activates the oxytocin neurones that project either to the pons (reticular formation, locus coeruleus), to the hippocampus, to the insula, or to the orbitofrontal cortex, leading to the transient feeling of wellbeing that follows yawning. This pathway is modulated by acetylcholine, serotonin, opioid peptides, sexual hormones, and orexin. The paper by Cattaneo et al provides important data on the crucial role of the lower brain stem.

Contagious yawning is an even more intriguing phenomenon. It is triggered by seeing, hearing, or even thinking about someone else yawning. Contagious yawning does not occur in species that do not recognise themselves in mirrors or in infants younger than two years old. The phenomenon has been investigated with functional magnetic resonance imaging, which implicated the precuneus or the posterior cingulate regions, functional regions associated with the identification of self referent information, a primitive form of empathy. Further studies are needed before conclusions can be drawn

“One person yawning sets off everyone else”
M‐Pierre Perriol and C Monaca
J Neurol Neurosurg Psychiatry. 2006 January; 77(1): 3

Ahmet Corak, M.D., PhD.
Marmara University
Department of Physiology