The Science of Yawning: New Insights into Brain Cooling and Fluid Flow

Researchers from the University of New South Wales and Neuroscience Research Australia have examined the physiological effects of yawning on the brain. Their findings were published in Respiratory Physiology & Neurobiology.

Study Methodology

The study involved 22 participants between the ages of 18 and 72. Researchers used MRI imaging to scan participants' heads and necks during yawns, deep breaths, stifled yawns, and normal breathing.

Key Findings

Cerebrospinal Fluid (CSF) Flow

The study observed that yawning reversed the flow of cerebrospinal fluid (CSF) in the brain.

This reversal was not observed in every case and occurred less often in male participants—a finding researchers attributed to possible scanner interference.

Brain Temperature Regulation

Yawning induced a flow of cooler blood into the brain, which may offset the movement of outgoing blood and CSF. This suggests a thermoregulatory function.

Distinct from Deep Breathing

The pattern of CSF flow during yawning was different from that observed during deep breathing. Neurologist Thomas Kalincik, who was not involved in the study, described this distinction as "new and unexpected."

Yawning Signatures

Each participant demonstrated a unique and consistent pattern of yawning motion, which researcher Adam Martinac termed a "yawning signature."

Statements from Researchers

"It was an exploratory study that then turned into something real." — Adam Martinac

Martinac noted that previous research on respiration did not find a link between oxygen levels and yawning.

Lead researcher Professor Lynn Bilston proposed that yawning likely plays a role in cleaning brain fluid, particularly near bedtime.

"What I find interesting and novel... is the difference between the flow of CSF during yawning and deep breathing." — Thomas Kalincik

Limitations and Unresolved Questions

• Preliminary findings: Researchers emphasized the results are not yet conclusive. Martinac said, "Our study has not determined anything related to human health specifically and improvements."
• The study did not determine whether yawning signatures are genetically or socially determined.
• The evolutionary reason for yawning is not fully understood.
• Both yawns and deep breaths increased blood flow leaving the brain.

Further Research

Martinac expressed interest in investigating the mechanics of yawning, noting that neurodegenerative diseases are linked to waste accumulation with age.