LOUD music played
on earphones causes deafness by having a similar effect on nerves as multiple
sclerosis (MS), scientists have learned.
New research
shows that noise levels above 110 decibels strip insulation from nerve fibres
carrying signals from the ear to the brain.
Loss of the
protective coating, called myelin, disrupts electrical nerve signals.
The same process,
this time due to an attack from the immune system, damages nerves in the brain
and results in MS.
Loud noises are
well known to lead to hearing problems such as temporary deafness or tinnitus
(ringing in the ears). But this is the first time scientists have been able to
identify the underlying damage to nerve cells.
The findings are
published in the journal Proceedings of the National Academy of Sciences.
Lead researcher
Dr Martine Hamann, from the University
of Leicester, said
"The research allows us to understand the pathway from exposure to loud
noises to hearing loss. Dissecting the cellular mechanisms underlying this
condition is likely to bring a very significant healthcare benefit to a wide
population. The work will help prevention as well as progression into finding
appropriate cures for hearing loss."
The scientists
found that myelin lost as a result of noise exposure regrows in time, meaning
hearing can recover.
"We now
understand why hearing loss can be reversible in certain cases," Dr Hamann
added. "We showed that the sheath around the auditory nerve is lost in
about half of the cells we looked at, a bit like stripping the electrical cable
linking an amplifier to the loudspeaker. The effect is reversible and after
three months, hearing has recovered and so has the sheath around the auditory
nerve."
The work is part
of ongoing research into the effects of loud noises on the cochlea nucleus, a
brainstem region that receives sound signals from the inner ear.
The team has
already shown that damage to cells in the cochlea nucleus can cause tinnitus
SOURCE: Independent
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