During yawning, there is a synchronous movement of cerebrospinal fluid and venous blood from the brain to the spinal cord, which contrasts with the process of deep breathing, where venous blood leaves the brain while cerebrospinal fluid enters it.
Additionally, yawning increases blood flow through the carotid artery by more than 30% compared to a deep inhalation. Scientists suggest that this is related to the simultaneous movement of venous blood and cerebrospinal fluid freeing up space in the cranial cavity, allowing arterial blood to flow in greater volume.
Although the volume of fluid moved during a single yawn is only a few milliliters, this effect was observed in all participants of the study. MRI showed that each volunteer yawned differently, recording unique patterns of tongue and throat muscle movements.
The mechanism of this phenomenon remains insufficiently studied. Researchers suggest that the coordinated action of the neck, tongue, and throat muscles may contribute to the "pumping" of fluid. Possible redistribution functions include thermoregulation, removal of metabolic waste, and optimization of brain function; however, these hypotheses require further confirmation.
