Capital Region Special Surgery Blog

Ahhh……. the good ol’ days. Going out with your buds to a summer rock concert, hanging out all day with some good, although loud, tunes. Maybe standing in front of those monolithic dental filling loosening speakers to get that extra rush. Maybe dancing the night away at that hip new club. Has anybody experienced the temporary decrease in hearing or the tinnitus (head noise) that occurs after that night? Well welcome to the “temporary threshold shift.” Here’s why it occurs (or so we think).

For a primer on this section please see how we hear on our web site

Noise induced hearing loss that is permanent is thought to occur because delicate hair cells within our inner ear have been stressed to breakage.

This is a picture of a pigeon cochlea showing the well ordered rows of hair cells. The white structures are “hair cell fibers”, actually stereocilia which are the pressure receptors that transducer the physical vibrations of sound into an electrical signal that goes to our brains. This particular “pigge” was listening to Mozart at a reasonable level.

This little “pigge” to the right went to see Aerosmith and sat right in front of the speakers for days on end (mixed in with some NASCAR). See the difference?

This type of physical damage is usually permanent and occurs only after many years of abuse.

So how does this temporary stuff happen? The running theory is based on the fact that the inner ear hair cells are very active metabolically. That means that they burn a lot of energy and as a result have a lot of byproducts. Some major byproducts of cellular respiration that have gotten a lot of attention are called free radicals and superoxides. One example of a free radical isozone. An example of a superoxide is hydrogen peroxide. While ozone may be great for keeping you from getting a sunburn and peroxide is great for cleaning boo boo’s (actually not so great) they are not very healthy to ingest. Our bodies constantly make these free radicals and oxides and our bodies are constantly trying to get rid of them.

The idea is that you make the hair cell work so hard that it creates these superoxides and free radicals. If the cell cannot get rid of them the cell can be damaged. 

Recently some researchers have been looking at using antioxidants to help these cells, and other body cells, out. Others don’t care about real research and have just tried to get rich off of the teaming millions that believe everything they hear. Some examples of antioxidant rich foods are: red wine, pomagranite juice, broccoli, red wine, vegetable juices, fruits, berries, and oh…. did I mention red wine. Pomagranite juice has twice the antioxidant value of red wine. I’ll have two glasses of Merlot then.

It turns out that Owls have fascinating ears. People have two ears for several reasons. One main one is that it allows us to detect the direction of sound. When a sound comes at us from one direction, say the right side, our right ear detects it a fraction of a second before the left one does (the time it takes for the sound to travel the foot or so between ears). This is called a phase delay. This is why people who have lost hearing in one ear have trouble detecting the direction of sound and why we recommend bilateral hearing aids, bilateral cochlear implants, etc.

Owls have taken it one step further as discussed bellow and in the web link. Their ears are assymetrically placed so that they can tiangulate the position of their prey not only in the horizontile direction but also where the prey is abobe or bellow them.

Some time ago I learned this while watching a special on owls with my 8 year old son. I had the brilliant idea of why we cannot place our bilateral cochlear implants asymetrically. I came rushing into work like a madman one day to tell our audiologist, Sharon Rende, all about what I learned the night before and how it was going to change how we placed implants into patients from this day foward. After asking me to stop drinking with my son while watching owl programs she thought that it was a stupid idea, and parents would not like it if their kids had only one implant on the top of their heads.

I sent an email about this to Ruth Litovsky PhD. She is a world renowned audiologist and researcher at Washington U. in St. Louis who specializes in the neural pathways for the detection of sound direction. Turns out that do not humans share the same neural pathway as owls. Hence we humans are not able to make sense of these auditory cues. Science marches on.

OWL HEARING

Because Owls are generally active at night, they have a highly developed auditory (hearing) system. The ears are located at the sides of the head, behind the eyes, and are covered by the feathers of the facial disc. The “Ear Tufts” visible on some species are not ears at all, but simply display feathers.
The shape of the ear opening (known as the aperture) depends on the species of Owl - in some species, the opening has a valve, called an operculum covering it . The opening varies from a small, round aperture to an oblong slit with a large operculum. All owls of the family Tytonidae have rounded openings with large opercula, while in Strigidae, the shape of the outer ear is more varied.

An Owl’s range of audible sounds is not unlike that of humans, but an Owl’s hearing is much more acute at certain frequencies enabling it to hear even the slightest movement of their prey in leaves or undergrowth.

Some Owl species have asymmetrically set ear openings (i.e. one ear is higher than the other) - in particular the strictly nocturnal species, such as the Barn Owl or the Tengmalm’s (Boreal) Owl. These species have a very pronounced facial disc, which acts like a “radar dish”, guiding sounds into the ear openings. The shape of the disc can be altered at will, using special facial muscles. Also, an Owl’s bill is pointed downward, increasing the surface area over which the soundwaves are collected by the facial disc. In 4 species (Ural, Great Gray, Boreal/Tengmalm’s & Saw-whet), the ear asymmetry is actually in the temporal parts of the skull, giving it a “lop-sided” appearance.

An owl uses these unique, sensitive ears to locate prey by listening for prey movements through ground cover such as leaves, foliage, or even snow. When a noise is heard, the owl is able to tell its direction because of the minute time difference in which the sound is perceived in the left and right ear. For example, if the sound was to the left of the owl, the left ear would hear it before the right ear. The owl then turns it’s head so the sound arrives at both ears simultaneously - then it knows the prey is right in front of it. Owls can detect a left/right time difference of about 0.00003 seconds (30 millionths of a second!)

An owl can also tell if the sound is higher or lower by using the asymmetrical or uneven Ear openings. In a Barn Owl, the left ear left opening is higher than the right - so a sound coming from below the owl’s line of sight will be louder in the right ear.

The translation of left, right, up and down signals are combined instantly in the owl’s brain, and create a mental image of the space where the sound source is located. Studies of owl brains have revealed that the medulla (the area in the brain associated with hearing) is much more complex than in other birds. A Barn Owl’s medulla is estimated to have at least 95,000 neurons - three times as many as a Crow.

Once the Oowl has determined the direction of its next victim, it will fly toward it, keeping its head in line with the direction of the last sound the prey made. If the prey moves, the owl is able to make corrections mid flight. When about 60 cm (24″) from the prey, the owl will bring its feet forward and spread its talons in an oval pattern, and, just before striking, will thrust it’s legs out in front of it’s face and often close it’s eyes before the kill.

References:
Campbell, Wayne. 1994. “Know Your Owls (CD-ROM)”. Axia Wildlife
Hollands, David. 1991. “Birds of the Night”. Reed Books
König, Weick and Becking. 1999. “Owls: A Guide to the Owls of the World”. Yale University Press
Long, Kim. 1998. “Owls: A Wildlife Handbook”. Johnson Books
Mikkola, Heimo. 1983. “Owls of Europe”. Buteo Books

David Foyt, M.D.
Capital Region Ear Institute
Clinical Associate Professor Surgery(Otolaryngology / Neurosurgery)

A patient came to me yesterday who suffers from presbystasis. This is a disorder in which both inner ears are weak and the person has difficulty maintaining balance. Often, time consuming vestibular physical therapy is the only available remedy. This patient had trouble taveling to our vestibular rehab center, so….. he did the next best thing. He brought the therapy home. He purchased an inexpensive foam board on which to practice his balance. The foam removes sensory clues that one would normallyget from the feet contacting the ground. This forces the balance system in the ears to function extra hard thus “exercising” the inner ear. A briliant and inexpnsive alternative.

Last week I walked into the office to witness one of those personal heartwarming moments that reminds me of why I went into hearing restortion surgery. One of our cochlear implant patients was in the office playing his violin. He had learned the instrument years ago as a child but had given it up when his hearing failed. He was cast into “musical darkness” for many years until he received his cochlear implants. The question I had was whether he was tuning his violin with his cochlear implants or his cochlear implants with his violin. “Both” he said.

David Foyt, M.D.
Capital Region Ear Institute
Clinical Associate Professor Surgery(Otolaryngology / Neurosurgery)