The results of the experiment showed that during yawning, the flow of cerebrospinal fluid and venous blood moves in sync—from the brain to the spinal cord. This contrasts with deep breathing, which leads to the outflow of venous blood from the brain and the influx of cerebrospinal fluid. Additionally, during yawning, blood flow through the carotid artery increased by more than 30% compared to a deep inhalation. According to the researchers, this coordinated movement of fluids frees up space in the cranial cavity, allowing more arterial blood to enter.
Although the volume of fluid moved during a single yawn is only a few milliliters, the effect was equally stable among all participants in the study. Each volunteer yawned in their own way, and MRI captured the individual patterns of tongue and throat muscle movement.
The exact mechanism of this process has not yet been established. Researchers suggest that the coordinated action of the neck, tongue, and throat muscles may contribute to the "pumping" of fluid. Possible functions of such redistribution include thermoregulation, removal of metabolic waste, and optimization of brain function; however, these hypotheses require further confirmation.
