Kamal Ghorui
Yawning is among the most common human behaviours. Often associated with fatigue or boredom, this habit, however, triggers a hidden brain process. Scientists have long believed it plays a biological role.A recent study published in Respiratory Physiology & Neurobiology, however, found that yawning could affect how the liquid flows in the brain. Scientists from the University of New South Wales used MRI technology to see what occurs when people yawn.The research found that yawning leads to a sudden change in the movement of the cerebrospinal fluid (CSF). This is further responsible for protecting the brain and spinal cord.What did the scans show?The scientists used 22 healthy participants in their experiment. They asked the subjects to yawn, take deep breaths, resist yawning, and breathe normally in an MRI machine.The experts assumed that yawning would be like deep breathing since both behaviours require a large inhalation. However, the scans demonstrated a notable difference between the two processes.When yawning, CSF moved away from the brain. However, deep breathing failed to cause this effect. Adam Martinac, a neuroscientist and lead author of the study, explained to New Scientist that the yawn was inducing a flow of the CSF in the opposite direction to what happens during deep breathing.Not all volunteers exhibited this behaviour, but the scientists concluded that the environment in the scanner could affect the results. Nevertheless, the effect was too obvious not to prompt some interesting discussions about the function of yawning.Why cerebrospinal fluid is essential for brain health?It protects the brain from injuries, transports nutrients, and clears out metabolic waste. In recent years, scientists became interested in its role in regulating cerebral blood flow.According to the National Institute of Health, cerebrospinal fluid flow facilitates metabolic waste clearance, particularly during sleep. Based on the new findings, yawning can momentarily impact this system when a person is awake.
Study finds yawning does something unexpected in your brain. Image credit – Gemini
Blood flow changes during yawningBesides the CSF movements, the MRI scans revealed that the yawn caused changes in cerebral blood flow. Both yawning and deep breathing stimulated blood outflow from the brain. Thus, there was more space for new blood to enter the brain.Meanwhile, blood flow to the brain via the carotid arteries rose by about a third in the initial stages of a yawn.The fluid and blood dynamics in conjunction seem to indicate that yawning might have an effect on the balance of pressure and circulation within the brain.Unique signature of every individualAn additional surprise came from the consistency of each participant’s yawn. Each person had unique features regarding the tongue and muscle motion during the process. Nevertheless, each individual repeated his/her own pattern each time when he/she yawned. Martinac noted that every person yawns differently. It’s akin to a fingerprint.The uniqueness of yawning patterns might be explained by the fact that yawning is driven by a central pattern generator located in the brain.Why do people yawn?At this stage, scientists can only hypothesise why yawning influences brain functions the way it does. Numerous theories exist.One of those is that yawning helps remove waste from the brain by regulating CSF dynamics. That might be related to the studies on neurodegenerative diseases and protein accumulation within the brain.Another theory proposes that yawning serves as a mechanism for maintaining brain temperature regulation.However, neither of these two theories is supported by the new MRI results. Instead, these results indicate the physiological significance of yawning in brain systems.A behaviour shrouded in mysteryIt is worth noting that yawns can be observed in numerous animal species, including humans, mammals, and reptiles. Moreover, yawns are contagious, adding yet another dimension to the topic.While common, yawns remain poorly understood from an evolutionary perspective.The researchers commented that yawning seems to be a very adaptive behaviour, emphasising that further investigations are required to elucidate its importance in brain physiology.In this context, the current study provides a significant hint that yawns are not merely reactions to exhaustion. Instead, yawning could be part of a complex brain homeostasis system.
