Fish and Hearing - New research shows how fish hear and make sounds at the same time.

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Subject: Fish and Hearing - New research shows how fish hear and make sounds at the same time.
Posted by:  HHIssu…@aol.com (HHIssu…@aol.com)
Date: 18 Aug 2005

source: bhNEWS

Advance for Audiologists, Issue date August 22, 2005
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Fish and Hearing

New research shows how fish hear and make sounds at the same time.

Cornell University researchers have learned how a common fish found
along the West Coast can hum and hear outside sounds at the same time.

The study marks the first time that scientists have found a direct
line of communication between the part of a vertebrate's brain that
controls the vocal muscle system and the part of the ear that hears
sound. The researchers believe that understanding the auditory system
of the plainfin midshipman fish (Porichthys notatus) - a 6- to 10-inch
fish found along the coastline from Alaska to California - will offer
insights into the hearing abilities of other vertebrates, including
humans.

The general pattern of connections between neurons in the auditory
system is the same in all vertebrates, including mammals. While humans
hear with the cochlea of the inner ear, the midshipman uses the
sacculus.

Because the study indicates a relationship between the ear and the
auditory and vocalization systems of the brain, it could help
scientists understand some of the mechanisms that contribute to
deafness.

"We've studied so many things about these fish, and I never cease to be
amazed by how similar the operation of their nervous system is to that
of mammals," said Andrew Bass, professor of neurobiology and behavior
at Cornell, and an author of the study published in the June 22 issue
of the Journal of Neuroscience. "You don't need to study a mammal to
understand what a mammal does."

The researchers found that as the fish's brain signals vocal muscles to
make sound, a number of synchronized actions take place. The ear and
brain are cued to the exact timing of a self-generated sound,
distinguishing it from outside sounds. Just prior to a voicing, the
brain warns the ear it should become less sensitive.

When analyzed closely, the vocalizations can be broken down into a
series of impulses separated in time by only milliseconds. The system
is timed only to block out sound at the exact moment when the fish
vocalizes, leaving the ear sensitive to outside noises during the
millisecond gaps when the fish is silent. Once an impulse for
vocalization ends, the brain decreases its messages to the ear, which
in turn makes the ear more receptive to external sound again. In fact,
for an instant following a vocalization, the ear may actually become
more sensitive than it was prior to the voicing.

By better understanding these complex systems, the study offers new
avenues for researchers to explore the causes of human deafness.

"Hearing loss is a major pathology that humans deal with," said Dr.
Bass. "And we don't understand that mechanism very well. Observing what
these neurons do may offer insights into what leads to hearing
deficits."

Only a few fish vocalize, but male plainfin midshipman fish hum to
attract a mate or grunt when stressed. When courting, the midshipman
hums continuously for up to two hours to attract a female, who may
deposit up to 200 eggs, which the male fertilizes. The next night, the
male hums again to attract a new mate. In one season, a successful male
may end up fertilizing several thousand eggs.

During mating season, houseboat owners in San Francisco Bay have
complained that their homes vibrate from the humming fish, which sound
like a high-speed motor running underwater.

Co-author Matthew Weeg received his doctorate from Cornell and
worked in Andrew Bass's laboratory before recently becoming a lecturer
at Colorado State University. The other co-author, Bruce Land, is a
senior research associate in Cornell's Department of Neurobiology and
Behavior.

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