Deafness Affects Birds' Vocal Ability
Research indicates that a songbird's singing ability begins to decay within 24 hours of the animal losing its hearing. The findings suggest deafness could penetrate much more rapidly and deeply into the brain than previously thought. The study, conducted by researchers at Duke University Medical Center and published in Neuron journal online (March 7), marks the first time scientists have been able to watch how deafening affects connections between nerve cells in a vocal motor area of the brain in a living animal.
Using a protein isolated from jellyfish that makes songbird nerve cells glow bright green when viewed under a laser-powered microscope, the authors determined that deafening triggered rapid changes to synapses.
The researchers also saw rapid changes in motor areas that control song—the bird's equivalent of speech—when hearing was lost. The study illuminated what happens in the living songbird brain, including the cell types involved. As the size and strength of nerve cell connections visibly changed, researchers could predict which songbirds would have worse songs in coming days.
Researchers hope this study will shed light on why and how some people's speech changes as their hearing starts to decline. Search doi: 10.1016/j.neuron.2011.12.038.
Noise-Induced Hearing Loss—16 Years Later
The results of a recent study in Occupational & Environmental Medicine (March 23) suggest that early-stage noise-induced hearing loss (NIHL) can be detected in young workers by measuring high-frequency changes in hearing acuity.
The study aimed to estimate strength of associations between occupational and recreational noise and chemical exposures and occurrence of early-stage NIHL, and to determine the extent to which the use of hearing protection mitigated early-stage NIHL.
Participants were 392 young adults who agreed to participate in a follow-up of a randomized controlled trial. Although the follow-up study was designed to observe long-term effects—up to 16 years—of a hearing conservation intervention for high school students, it also provided an opportunity to study the potential etiology of NIHL in this worker cohort. Study data were collected via exposure history questionnaires and clinical audiometric examinations.
Over the 16 years, the authors documented changes to hearing acuity that exceeded 15 dB at high frequencies in 42.8% of men and 27.7% of women. Analyses of risk factors for NIHL were limited to men—68% of the cohort—and showed that risks increased in association with higher levels of the most common recreational and occupational noise sources, as well as ototoxic chemical exposures. Search doi:10.1136/oemed-2011-100464.
Prednisolone Ineffective for Hearing Loss
Typical dosages of the corticosteroid prednisolone do not seem to influence recovery of idiopathic sudden sensorineural hearing loss, according to a paper published ahead-of-print in Otology & Neurotology.
Researchers conducted a randomized, triple-blind trial to compare the effects of prednisolone and placebo on the recovery of unilateral idiopathic sudden sensorineural hearing loss. The study was conducted in four tertiary and 10 secondary referral centers.
Of 103 randomly assigned patients, 93 were selected for treatment. The patients—ages 18 to 80 years—were seeking care within one week after onset of acute unilateral sensorineural hearing loss (a mean decrease of 30 dB or greater in the three most-affected contiguous frequencies).
Forty-seven patients received prednisolone—and 46 a placebo—in tapering doses from 60 mg for three days, and then 10 mg less each day for seven days. In cases of complete recovery, no more medication was given. In other subjects, medication continued at 10 mg per day until day 30. After three months, researchers conducted a final follow-up with audiogram.
Although researchers found no significant correlation between prednisolone treatment and hearing improvement, participants with vertigo—whether they received prednisolone or a placebo—experienced less hearing improvement. Search doi: 10.1097/MAO.0b013e31824b78da.