In the study, researchers from China conducted an experiment on mice genetically modified to be in the early stages of Parkinson's disease, a neurodegenerative disorder caused by the death of dopamine-producing nerve cells in the brain. Those affected typically experience tremors, muscle stiffness, and problems with speech and balance—symptoms that gradually worsen over time.
The mice were exposed to sounds ranging in intensity from 85 to 100 decibels — equivalent to the noise of a lawnmower or electric blender — either in the form of short pulses or repeated daily exposure.
The results showed that just one hour of exposure was enough to induce slowed movement and loss of balance compared to mice that were not exposed to the noise. Mice subjected to the experiment for one hour daily for a week developed chronic motor disorders that persisted even after exposure ceased.
The researchers found that a region in the brain known as the inferior colliculus — which is responsible for processing sound — is directly linked to the substantia nigra, the part of the brain responsible for producing dopamine that is severely damaged in Parkinson's disease.
The analysis showed that chronic stimulation of the inferior colliculus leads to the death of dopamine-producing cells and a decrease in the levels of a protein called vesicular monoamine transporter (VMAT2), which is responsible for transporting neurotransmitters such as dopamine and serotonin within nerve cells.
Conversely, the team found that inhibiting the activity of the inferior colliculus increases the production of this protein, which may help reverse the effects of noise in mice with the disease in its early stages.
The researchers noted that these findings highlight the potential role of environmental factors, such as noise and pollution, in accelerating the progression of Parkinson's disease, although the study was conducted only on animals.
The research team wrote: "It was striking to observe how exposure to environmental noise leads to degeneration of dopamine-producing neurons and the associated motor deficits, providing new insights into the non-genetic factors causing Parkinson's disease."
Although there is currently no cure for Parkinson's disease, medications and supportive therapies help compensate for the dopamine deficiency and alleviate symptoms. Levodopa is the most commonly used medication; it crosses the blood-brain barrier and is converted into dopamine, which improves balance and reduces tremors.
The study was published in the journal PLOS Biology.