Dear Doctors: I have always liked how yawning feels and wondered what it's for. I just read there is new information about how yawning affects your brain. Do you know anything about that? Also, do we know yet why yawning is so contagious? I've even been able to get my dog to yawn.

Dear Reader: Your questions about yawning echo across millennia. A physical reflex still shrouded in mystery, the search for an answer to why we yawn dates back at least to the ancient Greeks. Aristotle and Hippocrates favored a theory of ventilation. Less scientific notions have leaned into the mystical. Some have guessed soul slippage, a leaching of life force or spirits entering or leaving the body. What we do know for sure is that virtually all primates yawn. The behavior has also been observed in birds and even some fish. And you're right that it's contagious. It would be surprising if a portion of readers hadn't already stifled, or given in to, a yawn while reading this column.

Now, the results of a small study suggest the ancient Greeks weren't that far off the mark. Researchers in Australia have found that yawning can affect the movement of cerebrospinal fluid in the brain. Cerebrospinal fluid, or CSF, is a clear liquid produced in the brain. It helps to cushion and protect this critical organ. CSF also carries nutrients and removes waste.

In their study, scientists performed MRI scans of the brains of 22 healthy volunteers as they breathed normally, took deep breaths, yawned and stifled a yawn. Because deep breathing and yawning share similar physical actions, the researchers expected to see similar MRI results. However, the scans showed that during a yawn, cerebrospinal fluid was often transported away from the brain. This was the opposite of what happened during a deep breath.

This led the researchers to conclude that, rather than a variant of deep breathing, yawning is a distinct maneuver that reorients the flow of CSF. As for why that is metabolically advantageous, the answer is not yet clear. Theories include the idea that the movement of CSF plays a role in cooling the brain, aids in the removal of metabolic waste or amps up the alertness that is critical to scanning for danger.

While the findings in this study took a surprising turn, it is important to note the small sample size. In addition, the movement of CSF during a yawn was not observed 100% of the time. Also, the effect was observed more often in women than in men. In an interesting side note, each person yawned the same way and in the same pattern. Also, each study participant's yawn sequence was unique. Sadly, no light was shed on why yawns are so contagious.

As with all preliminary research, larger and repeated studies are needed to affirm the results. However, even without a conclusive outcome, the study bolsters the existing idea that yawning likely serves a specific purpose. It's something to consider next time you give in to a yawn, or to the urge to get your dog to yawn along with you.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

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Dear Doctors: My 11-year-old son was diagnosed with sudden sensorineural hearing loss. He’s been treated with steroids and 10 HBOT sessions, with a small increase in hearing. I’m struggling to find any information regarding HBOT for children. Is there literature or experience in similar cases?

Dear Reader: For those who are not familiar, sudden sensorineural hearing loss, or SSHL, is sometimes called sudden deafness. It is a specific diagnosis in which hearing loss has dropped from normal to significantly diminished in three days or less. The word "sensorineural" means the doctor believes the structures of the inner ear and the neural pathways to the brain are involved. This diagnosis requires a loss of a minimum of 30 decibels. This is enough to make everyday conversation difficult to hear. Because high, low and middle registers are affected, the audio of daily life for someone with SSHL sounds like a speaker set on low.

Another important part of your question is about a medical treatment called hyperbaric oxygen therapy (HBOT). An individual breathes pure oxygen for an extended period of time while in a pressurized chamber or room. Because some cases of SSHL can involve impaired blood flow to the structures of the ear, HBOT is sometimes recommended. Treatments typically consist of a set sequence of daily sessions of 90 minutes each. The number of treatments depends on the condition involved.

The reason you have been struggling to find information about the efficacy of this treatment for your son's diagnosis is that, although SSHL can occur at any age, it is rare in children. The majority of cases are seen in adults, often in their late 40s and early 50s. It’s often difficult to identify a clear reason for the condition in patients of any age. Contributing factors can include viral illness, head trauma or a noise injury. Other factors can be autoimmune or vascular diseases, neurological disorders or side effects of certain medications.

When it comes to understanding your son's condition and evaluating future treatments, the available information comes from studies in adults. The limited data that does reference children comes from case studies. These are narratives in which a doctor outlines what happened with a specific patient. Case studies include symptoms, treatment options, decisions made and their outcomes. While useful, they lack the heft of a study with a large sample size.

Data suggest that HBOT can offer modest improvements in cases of SSHL. A small study in Turkey, which looked at 15 children with the condition, saw a wide range of responses. Half reported a complete recovery of hearing, 25% had small to partial recovery and 25% were unchanged. As with your son, they received steroids as well.

It is important to note that, because the study was so small, we should interpret the results with caution. They do not predict how any one child will respond. It is likely your son’s ENT can help put the findings into context, and you can make treatment decisions together.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I read your column about the scent of skin secretion changes in Parkinson's disease. A couple of years ago, I read about training canines to smell and detect lung cancer. Has there been additional work done in training canines for disease detection?

Dear Reader: Your question leads us to the fascinating and remarkable canine nose. Researchers guess that a dog's sense of smell is between 10,000 and 100,000 times more sensitive than ours. We make do with a mere 6 million scent receptors, while dogs have up to 300 million. A dog's brain also devotes about 40 times more of its real estate to decoding smell than ours does. This all adds up to a sense of smell so sensitive that it's believed a dog can detect a single molecule.

And that's where the idea of using dogs in medical diagnosis comes into play. The column you referenced explored changes that occur in the skin of people living with Parkinson's disease. These changes cause a specific scent that dogs can detect, even in minute amounts. The idea is that we could use this scent as a biomarker for early diagnosis of the disease. We are already using dogs to identify the metabolic changes that happen before an epileptic seizure. They can detect changes in blood sugar in people living with diabetes. As you point out, they can also detect certain cancers. More recently, we discovered dogs are surprisingly accurate in identifying COVID-19 infection.

All of this is possible because our bodies continually produce and release volatile organic compounds, or VOCs. These are clusters of distinct airborne molecules that humans release through sweat, breath or urine. VOCs have distinct and identifiable scents that are practically tailor-made for the nuances of the dog nose.

Although this represents a promising direction, enlisting the canine sense of smell in medical care faces some real hurdles. A big one is this requires a lot of training. First, we have to teach a dog to recognize and focus on a specific scent. Then there's an extended period of testing for reliability. Depending on the disease or condition, it can take months to a year or more for a dog to be ready to deal with patients in a clinical setting. Other considerations are stress and nose fatigue, a real phenomenon. Repeated exposure to scents can temporarily dull sensitivity.

Despite these limitations, a potential role for dogs in diagnostic medicine continues to expand. Proposed and ongoing studies are being done all over the world. There are studies for diagnosis of breast cancer through sweat samples. Research is expanding into a wider range of viral and infectious diseases. There are also efforts to combine dog research with chemical profiling to develop medical instruments based on VOC compounds. There is also encouraging news for our four-footed friends. An ongoing study is looking into a sniff test for an aggressive cancer found in dogs. Someday dogs could benefit from diagnosis by their own superpower.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)