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| We all yawn but none of us know why. |
One of the few things we know about yawning is that it is contagious. In fact, because you are currently reading about yawning, you are highly likely to feel the urge yourself. Attempting to suppress this urge will be futile; it is a powerful and unstoppable desire.
The fact that we can catch yawns is well known, but scientists are yet to understand why they are contagious and even why we yawn at all. Although research into yawning might seem whimsical, there is good reason to give it more attention: it may offer insight into a range of conditions, including Tourette's syndrome.
Dissecting a yawn
Researchers from the University of Nottingham in the United Kingdom set out to investigate yawn contagion and how it might be triggered by primitive reflexes in the primary motor cortex.
"there are many theories for why we yawn (e.g., lack of oxygen, to cool the brain, because we are tired, etc., etc.) but the evidence for these is lacking. The popular theory for contagious yawning is that it is linked with empathy for others, mimicry, and social bonding. Again the evidence for this is weak. I still think that much more research is required to understand the function and biology of yawning."
The contagious quality of yawning is particularly strong. Despite the fact that we take it for granted, it is impressively pervasive. when I teach about yawning, I can get most of the class yawning. (Note, this doesn't happen for my other lectures)."
Scientists believe that understanding yawn contagion and our ability (or inability) to suppress the urge might provide a deeper understanding of unrelated conditions. In particular, it might give insight into conditions that include echophenomena, which are automatic imitations that occur without awareness.
"We suggest that these findings may be particularly important in understanding further the association between motor excitability and the occurrence of echophenomena in a wide range of clinical conditions that have been linked to increased cortical excitability and/or decreased physiological inhibition such as epilepsy, dementia, autism, and Tourette's syndrome."
What happens when we 'catch' a yawn?
Exactly what happens in the brain during echophenomena is not known, although there are some theories. Some scientists believe that it might be linked to disinhibition of the human mirror-neuron system, which fires when the body completes an action as well as when it observes an action in another person.
The mirror-neuron system is also thought to be involved in synchronizing social behavior and empathy. However, current evidence for its role in yawning is lacking.
Echophenomena are also thought to involve hyper-excitability in the cortical motor areas, which are regions of the brain involved in the control, planning, and execution of movements.
For this new study, 36 participants watched a video of someone yawning and were asked to either resist the urge to yawn or to allow it. The resulting yawns (and stifled yawns) were counted, and the participants' perceived urge to yawn was monitored throughout. By using TMS, the team could also affect the urge to yawn.
To investigate the neural basis of yawning further, the team used transcranial magnetic stimulation (TMS), which is a noninvasive technique that stimulates nerve cells using magnetic fields.
The researchers found that suppressing a yawn actually increased the urge and did not significantly reduce the number of yawns.
"Using electrical stimulation we were able to increase excitability and, in doing so, increase the propensity for contagious yawning. In Tourettes, if we could reduce the excitability, we might reduce the ticks, and that's what we are working on."
Predicting the propensity to catch a yawn
Aside from stimulating brain regions, the team measured cortical excitability in the volunteers. They found that levels of cortical excitability and physiological inhibition of the primary motor cortex could predict how susceptible each individual would be to catching a yawn.
MNT asked Prof. Jackson whether the results surprised them. He said, "I guess we anticipated that the propensity for contagious yawning might be linked to the excitability of the motor brain, but I think we were surprised by how much of the individual variability in yawning (around 50 percent) could be explained by individual variability in measures of physiological inhibition and excitability of the motor cortex."
Although there is still much to learn about yawns and echophenomena, these findings lay some groundwork. Prof. Jackson says, "If we can understand how alterations in cortical excitability give rise to neural disorders we can potentially reverse them."
"We are looking for potential non-drug, personalized treatments using TMS that might be effective in modulating imbalances in the brain networks."
Prof. Jackson plans to continue his investigations into the realms of the yawn. He told MNT about the questions generated by the current study.
"First, how do instructions to resist yawning influence the physiological mechanisms that give rise to yawning? Second, we have shown that yawning and the urge-to-yawn can be dissociated. We plan to explore further the neural basis for the urge-to-yawn (which we suspect is upstream of the motor cortex)."
