Questions: Why do your eardrums move when your eyes move?

I figured I was just getting old.

My hearing has been getting worse, bad enough that I finally went to the doctor on Tuesday.

She, along with a nurse, managed to extract two quarter-sized pieces of what looked like fungal felt, one from each ear. She prescribed some antibiotics to see if the swelling would go down.

My hearing and balance improved immediately.

Which prompted a question that Ed Yong of The Atlantic has ventured to answer: Why do eardrums move when your eyeballs move?

As your eyes flitted right, both eardrums bulged to the left, one inward and one outward. They then bounced back and forth a few times, before coming to a halt. When you looked left, they bulged to the right, and oscillated again.

These wobbles happen every time you move your eyes, whether or not there’s external noise. The bigger the movement, the bigger the wobble. But no one knows why they happen. And until Jennifer Groh, from Duke University, discovered them, no one even knew that they happened at all.

Groh has long been interested in how the brain connects information from our eyes and ears. In a loud party, for example, we automatically read the lips of our conversational partners to interpret any unintelligible sounds. For that to work, the brain has to align visual and auditory information in space, so it knows that those sounds are coming from those lips. And that’s easier said than done, because our ears are obviously fixed on our heads but our eyes are constantly moving. They flit all over the space in front of us, roughly three times a second. Every such movement changes the spatial relationships between what we see and what we hear. So how does the brain unite those streams of information? And where?

“Historically, people have thought that information enters the ear and the eye separately, and that eventually it’s combined,” says Nina Kraus from Northwestern University. But Groh’s experiment, she says, suggests that this act of combination happens much earlier. The eardrum, after all, is responsible for converting vibrations in the air around us into vibrations in the liquid within our heads. It’s where hearing effectively begins. And if it wobbles as our eyes shift, then this suggests that vision might affect hearing “at the earliest possible point,” says Kraus.

Kurtis Gruters and David Murphy, two members of Groh’s team, detected the wobbling eardrums in the simplest possible way. They stuck microphones in the ears of several volunteers, and asked them to look at different targets. As their eyes moved, so did their eardrums. Like actual tiny drums, these vibrating membranes created small sounds, which the microphones could detect. That’s how the team showed that the eardrum oscillations match the direction and strength of the eyes’ movements.

They also found that the eardrums start to wobble about 10 milliseconds before the eyes. This suggest that the ears aren’t reacting to what’s happening in the eyes. Instead, Groh says, “the brain is saying: I am about to move the eyes; ears, get ready.”

Barbara Shinn-Cunningham, from Boston University, also studies the neuroscience of hearing, and she is more circumspect. “It is a very interesting and previously unknown phenomenon, which may turn out to be incredibly important,” she says, “But so far, there is no evidence it is. We just don’t yet know why it happens or what it means.”

Chobani yogurt mold not so harmless in animal models

That mold in Chobani yogurt that most said was harmless even though over 200 people reported getting sick? Not so harmless.

chobaniA team of medical researchers led from Duke University reports in mBio, the open access journal of the American Society for Microbiology:

The U.S. Food and Drug Administration reported that yogurt products were contaminated with M. circinelloides, a mucoralean fungal pathogen, and >200 consumers complained of symptoms, including vomiting, nausea, and diarrhea. The manufacturer voluntarily withdrew the affected yogurt products from the market. Compared to other food-borne pathogens, including bacteria, viruses, and parasites, less focus has been placed on the risk of fungal pathogens. This study evaluates the potential risk from the food-borne fungal pathogen M. circinelloides that was isolated from the contaminated commercial yogurt. We successfully cultured an M. circinelloides isolate and found that the isolate belongs to the species M. circinelloides f. circinelloides, which is often associated with human infections. In murine and insect host models, the isolate was virulent. While information disseminated in the popular press would suggest this fungal contaminant poses little or no risk to consumers, our results show instead that it is capable of causing significant infections in animals.

 Analysis of a food-borne fungal pathogen outbreak: virulence and genome of a Mucor circinelloides isolate from yogurt

mBio vol. 5 no. 4 e01390-14

chobani.yogurtSoo Chan Lee, R. Blake Billmyre, Alicia Li, Sandra Carson, Sean M. Sykes, Eun Young Huh, Piotr Mieczkowski, Dennis C. Ko, Christina A. Cuomo, Joseph Heitman

http://mbio.asm.org/content/5/4/e01390-14.executive-summary