Constant noise exposure causes cognitive decline in rats

by Daniel Fink, MD, Chair, The Quiet Coalition

Photo credit: Nikolett Emmert

A fascinating research study from the Military Medical Sciences Academy in Tianjin, China found that continuous noise exposure caused brain damage and cognitive decline in rats. Continuous noise exposure is rare in civilian life, whether at work or at play, and also unusual for those serving in armies or air forces, but it is a problem for sailors at sea.

I offer three cautions before you read: I lack the technical background to understand the details of the methods used; the research was done on 20 rats and needs confirmation; and its relevance to humans has yet to be determined.

The study found that continuous noise exposure at 95 decibels (dB) from 8 a.m. to 4 p.m. and then 75 dB for the other 16 hours of the day led to morphological and biochemical changes in cells in the brain’s hippocampus region and to cell death. The hippocampus is involved in converting short-term memories into long-term memory, as well as emotional processing and learning. Before the animals were sacrificed for the anatomic and biochemical studies of their brain, behavioral testing showed impaired performance.

These findings may be most applicable to sailors at sea, but if continuous noise damages the brain, I wouldn’t be surprised if subsequent research showed that shorter noise exposures also caused brain damage. The association between hearing loss and dementia is well known. Perhaps the dementia isn’t just from loss of auditory input and social isolation, but also involves direct noise-induced damage to the hippocampus as well. Exposure to 95 dB sound is rare outside the military, but exposure to 75 dB sound at work and in everyday life isn’t.

A 2012 study by Flamme and colleagues in quiet Kalamazoo, Michigan, not in noisy New York City, found that daily noise exposures averaged 79 dB for men and 77 dB for women, measured as 8-hour equivalents.

Again, the findings may or may not be relevant to the public, but I think they provide additional evidence about the dangers of noise for humans, the harm caused by noise and additional support for my frequent tagline for these blog posts: a quieter world will be a better and healthier world for all.