A groundbreaking study has revealed that yawning plays an important and previously unnoticed role in regulating fluids within the brain, and it has also explained what actually happens when a person tries to suppress a yawn.
Researchers used magnetic resonance imaging to study 22 healthy individuals, comparing the effect of yawning on the flow of cerebrospinal fluid – the fluid that helps remove waste and transport essential chemicals from the brain, maintaining pressure balance and supporting the overall health of this vital organ – compared to other movements such as normal breathing, deep breathing, and suppressed yawning.
The team found that yawning reorganizes the pathways for the flow of this fluid out of the brain and increases its speed compared to normal breathing, meaning that it has a "functional physiological purpose" and is not just a social signal of tiredness.
Interestingly, the study revealed that while deep breathing also increased fluid flow, yawning was "frequently associated" with fluid flowing outwards, whereas deep breathing showed a flow in the opposite direction.
Contagious yawning (which is transmitted from person to person) also produced a noticeable flow of fluid during the exhalation phase, which did not occur during normal or deep breathing.
The researchers confirmed that the muscular movements of the jaw, head, and neck were almost identical every time the person yawned, proving that it is an involuntary movement controlled by the brainstem.
As for those who try to suppress their yawns, the study says that suppressed yawns lasted for roughly the same duration as free yawns, meaning that suppression doesn't affect the internal process. Scientists explain this by saying, "Once started, yawning continues as an organized sequence that can be partially concealed but is difficult to completely interrupt." Interestingly, the study also noted that each person yawns slightly differently
In addition to regulating fluids, the flow pattern observed during yawning suggests that it also affects the transport of dissolved substances and heat exchange within the brain. The study notes that the alignment of cerebrospinal fluid flow with venous blood flow, and the increase in carotid arterial blood flow during yawning, may improve heat exchange and contribute to brain cooling
The study concludes by saying that "yawning appears to be a highly adaptive behavior, and further research into its physiological significance may be fruitful." If these findings are confirmed by more specialized brain studies, they may provide deeper insights into conditions associated with impaired cerebrospinal fluid flow, such as migraine headaches.
