Loud music played on earphones causes deafness in patients 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.