Loud sound may pose more harm than we thought


NEW YORK — Matt Gar­lock has trou­ble mak­ing out what his friends say in loud bars, but when he got a hear­ing test, the re­sult was nor­mal. Re­cent re­search may have found an ex­pla­na­tion for prob­lems like his, some­thing called “hid­den hear­ing loss.”

Sci­en­tists have been find­ing ev­i­dence that loud noise — from rock con­certs, leaf blow­ers, power tools and the like — dam­ages our hear­ing in a pre­vi­ously un­sus­pected way. It may not be im­me­di­ately no­tice­able, and it does not show up in stan­dard hear­ing tests.

But over time, Har­vard re­searcher M. Charles Liber­man says, it can rob our abil­ity to un­der­stand con­ver­sa­tion in a noisy set­ting. It may also help ex­plain why peo­ple have more trou­ble do­ing that as they age. And it may lead to per­sis­tent ring­ing in the ears.

The bot­tom line: “Noise is more dan­ger­ous than we thought.”

His work has been done al­most ex­clu­sively in an­i­mals. No­body knows how much it ex­plains hear­ing loss in peo­ple or how wide­spread it may be in the pop­u­la­tion. But he and oth­ers are al­ready work­ing on po­ten­tial treat­ments.

To un­der­stand Liber­man’s re­search, it helps to know just how we hear. When sound en­ters our ears, it’s picked up by so-called hair cells. They con­vert sound waves to sig­nals that are car­ried by nerves to the brain. Peo­ple can lose hair cells for a num­ber of rea­sons — from loud noise or some drugs, or sim­ple ag­ing — and our hear­ing de­grades as those sen­sors are lost.

That loss is what is picked up by a stan­dard test called an au­dio­gram that mea­sures how soft a noise we can hear in a quiet environment.

Liber­man’s work sug­gests that there’s an­other kind of dam­age that doesn’t kill off hair cells, but which leads to ex­pe­ri­ences like Gar­lock’s.

A 29-year-old sys­tems en­gi­neer who lives near Bos­ton, Gar­lock is a veteran of rock con­certs.

“You come home and you get that ring­ing in your ears that lasts for a few days and then it goes away,” he said.

But af­ter he went to Las Ve­gas for a friend’s birth­day, and vis­ited a cou­ple of dance clubs, it didn’t go away. So he had the au­dio­gram done, in 2015, and his score was nor­mal.

Last fall, he came across a news story about a study co-au­thored by Liber­man. It was a fol­low-up to Liber­mans’ ear­lier work that sug­gests loud noise dam­ages the del­i­cate con­nec­tions be­tween hair cells and the nerves that carry the hear­ing sig­nal to the brain.

The news story said this can cause not only per­sis­tent ring­ing in the ears, but also a lin­ger­ing dif­fi­culty in un­der­stand­ing con­ver­sa­tions in back­ground noise. Af­ter the Ve­gas trip, Gar­lock sensed he had that prob­lem him­self.

“I no­tice my­self lean­ing in and ask­ing peo­ple to re­peat them­selves, but I don’t no­tice any­body else do­ing that,” he said.

Gar­lock emailed one of Liber­man’s col­leagues and vol­un­teered for any fol­low-up stud­ies.

The con­nec­tions be­tween hair cells are called synapses, and a given hair cell has many of them. An­i­mal stud­ies sug­gest you could lose more than half of your synapses with­out any ef­fect on how you score on an au­dio­gram.

But it turns out, Liber­man says, that los­ing enough synapses erodes the mes­sage the nerves de­liver to the brain, wip­ing out de­tails that are cru­cial for sift­ing con­ver­sa­tion out from back­ground noise. It’s as if there’s a big Jum­botron show­ing a pic­ture, he says, but as more and more of its bulbs go black, it gets harder and harder to re­al­ize what the pic­ture shows.


Matt Gar­lock, of Mans­field, Mass., poses for a photo in a bar in Somerville, Mass. The 29-year old has trou­ble mak­ing out what his friends say in loud bars, but when he got a hear­ing test, the re­sult was nor­mal.

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