The Physiology and Mysteries of Yawning: From Brain Cooling to Contagion

By: Nesredin Hassen Yesuf

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Introduction

Yawning is a universal, involuntary reflex characterized by a widely gaped mouth and deep inhalation. Although commonly associated with fatigue or boredom, yawning remains poorly understood. Contemporary research explores its roles in brain cooling, arousal, and social communication, highlighting yawning’s multifaceted nature.

Physiological Mechanisms and Functions

Historically, yawning was thought to help increase blood oxygen levels—but studies in the 1980s disproved this [1]. Current research offers more supported theories:

Brain Cooling Hypothesis

Yawning may regulate brain temperature. The mechanism includes increased facial and neck blood flow and inhalation of cool air, promoting convective heat loss and thermal regulation [2,3]. Physiological measurements support this model: yawning increases heart rate and lung volume—changes more pronounced than those seen in deep breathing alone [2].

State-Change and Arousal Hypotheses

Yawning often occurs during behavioral transitions, such as waking or shifts in alertness. It may act as a reset mechanism to stabilize cortical arousal [2].

Figure 1: Physiological effects of yawning: brain cooling, oxygen and carbon dioxide regulation, and others.

Contagious Yawning: Social Dimensions

Yawning is highly contagious—triggered by seeing, hearing, or even thinking about yawning. Estimates suggest that most individuals respond within minutes [4]. In non-human primates like gelada baboons, contagion correlates with social bonding, suggesting an emotional dimension [5].

However, the empathy hypothesis remains contested: while some studies link contagious yawning to higher empathy and familiar relationships, others dispute its direct relationship, calling for more rigorous investigation [6,7].

Clinical Relevance and Pathological Yawning

Although occasional yawning is benign, excessive yawning (more than ~3 yawns per minute) can indicate underlying pathology. It is observed in conditions including sleep disorders (e.g., sleep apnea), neurological diseases (e.g., multiple sclerosis, brainstem lesions), migraine, and epilepsy [8,9]. In epilepsy, ictal yawning has lateralizing value in temporal lobe seizures [10].

Conclusion

Yawning remains a captivating and partly unresolved phenomenon. Emerging evidence suggests functions in thermoregulation and arousal, while contagious yawning may reflect social and neural processes. Understanding pathological yawning reinforces its diagnostic relevance. Far from being a trivial reflex, yawning bridges neurophysiology, behavior, and clinical neurology.

References

1. Provine RR, Tate BC, Geldmacher LL. Yawning: no effect of 45% C O₂, 100% O₂, or exercise. Behav Neural Biol. 1987;48(3):382–93.

2. Corey TP, Shoup-Knox ML, Gordis EB, Gallup GG Jr. Changes in physiology before, during, and after yawning. Front Evol Neurosci. 2011;3:7.

3. Gallup AC, Gallup GG Jr. Brain cooling in the yawning response: an observational study testing the thermoregulatory hypothesis. Physiol Behav. 2007;90(4):567–73.

4. Norscia I, Palagi E. Yawn contagion and empathy in Homo sapiens. PLoS One. 2011;6(12):e28472.

5. Norscia I, Zanoli A, Gamba M, Palagi E. Auditory contagious yawning is highest between friends and family members: support to the emotional bias hypothesis. Front Psychol. 2020;11:183.

6. Massen JJ, Verstappen MC, de Vries H. Why contagious yawning does not (yet) equate to empathy. Neurosci Biobehav Rev. 2017;80:573–85.

7. Platek SM, Mohamed FB, Gallup GG Jr. Contagious yawning and the brain. Cogn Brain Res. 2005;23(2–3):448–52.

8. Verywell Health. Excessive yawning. (2022) [online] Available from web.

9. SciELO. Yawning in neurology: a review. Arq Neuropsiquiatr. 2019;77(4):235–42.

10. Specchio LM, Bilo L, Capovilla G, Canevini MP. Periictal yawning in temporal lobe epilepsy. Epilepsy Behav. 2011;22(4):666–8.

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