A groundbreaking new study has uncovered that yawning may play an overlooked role in regulating fluids within the brain, while also shedding light on what occurs when individuals attempt to suppress a yawn. Previously, it was widely believed that this behaviour evolved primarily to regulate oxygen levels, with alternative theories suggesting it served as a social signal to indicate tiredness to others of the same species.
How Yawning Affects Brain Fluid
Using MRI scans, the research revealed that yawning reorganises the flow of cerebrospinal fluid out of the brain. This fluid is known to help remove waste products and transport essential chemicals, thereby maintaining pressure balance and supporting overall brain health. The study also observed that each person yawns in a slightly unique manner.
Published in the journal Respiratory Physiology & Neurobiology, the study notes: “Yawning appears to be a highly adaptive behaviour and further research into its physiological significance may prove fruitful.”
Coordinated Movements and Fluid Flow
Yawning involves a coordinated motion of the jaw, head, and neck in a consistent, repeatable pattern. These movements influence the flow of cerebrospinal fluid around the brain and spinal cord. The study assessed how yawning affected fluid-flow pathways near the brainstem and upper spine of 22 healthy participants, comparing it to normal and deep breathing, as well as stifled yawns.
Researchers found that yawning increased cerebrospinal fluid flow compared to regular breathing, indicating it has a “functional physiological purpose” beyond being a social cue for tiredness. While deep breaths also boosted fluid flow, yawning was “more frequently” associated with cerebrospinal fluid outflow. Deep breathing, in contrast, showed counter-directional fluid flow.
Contagious Yawning and Involuntary Nature
Even contagious yawning elicited a marked flow of cerebrospinal fluid during the expiratory phase, which was not apparent during deep or normal breathing. The study confirmed that muscle actions were nearly identical each time a person yawned, reinforcing that yawning is an involuntary movement controlled by the brainstem.
Notably, stifled yawns lasted nearly the same duration as uninhibited yawns, meaning that suppressing a yawn does not affect the underlying process. “Once initiated, yawning proceeds as a structured sequence that can be partially masked but is difficult to fully interrupt,” scientists explained.
Implications for Brain Cooling and Migraine
The flow pattern observed during yawns also suggests influences on solute transport and heat exchange in the brain. “Alignment of cerebrospinal and venous blood flow, and increased carotid arterial blood inflow, during yawning may also optimise heat exchange, contributing to cooling of the brain,” the study notes.
If confirmed with more targeted brain studies, these findings could provide further insights into conditions involving impaired cerebrospinal fluid flows, such as migraine.
