Source: WDDTY, July / August 2021. pp 28.29
In the brain, not the ears
Although tinnitus may begin as an injury to ear cells, it’s accepted science now that the condition has implications beyond the ears to the brain. Josef Rauschecker and his colleagues in the Department of Neuroscience, the Division of Audiology, and the Department of Otolaryngology at Georgetown University have used brain imaging studies to reveal some other scary results: they observed a significant loss of volume in an area located in the frontal lobe of the brain in people with tinnitus.
Researchers at the University of Illinois found that chronic tinnitus is also linked to changes in a region of the brain called the precuneus, part of the parietal lobes that sit near the top of the skull. The precuneus is connected to two inversely related networks in the brain: the “dorsal attention network,” activated by stimulation from incoming sensory information like touch and noise, and the “default mode network,” which operates when the brain is at rest and not occupied by anything in particular.
“When the default mode network is on, the dorsal attention network is off, and vice versa. We found that the precuneus in tinnitus patients seems to be playing a role in that relationship,” said tinnitus researcher Sara Schmidt.
The University of Illinois team found that in patients with chronic tinnitus, the dorsal attention network is working more often than the default mode network, which means the brain isn’t relaxing and disengaging from surrounding stimuli, creating the potential for mental fatigue. And the more severe the tinnitus, the more activated the dorsal attention network.
“This could explain why many reports being tired more often. Additionally, their attention may be engaged more with their tinnitus than necessary, and that may lessen their attention to other things,” University of Illinois professor of speech and hearing science Fatima Husain said. “If you have bothersome tinnitus, this may be why you have concentration issues.”
Interestingly, patients with recent-onset tinnitus did not show differences in their precuneus network connections compared to controls, suggesting that the changes in the brain come on after the tinnitus, not the other way around.
Alzheimer’s and Parkinson’s link
Tinnitus tends to increase with age, and studies have found that hearing loss is associated with dementia and impaired memory, but a 2019 study published in Scientific Reports was the first to look at tinnitus, Parkinson’s, and Alzheimer’s diseases systematically in a population-based way.
A team of Taiwanese researchers used health records to identify 12,657 tinnitus patients and 25,314 control patients without tinnitus. Over a 10-year follow-up period, 398 of those with tinnitus (3.1 percent) and 501 without (2.0 percent) developed Alzheimer’s, and 211 tinnitus patients (1.7 percent) and 249 control patients (1.0 percent) developed Parkinson’s.
After adjusting for other potential influencing factors like diabetes, head injuries, and income, the researchers determined that patients with tinnitus were 1.54 times more likely to develop Alzheimer’s and 1.56 times more likely to develop Parkinson’s.
A possible mechanism for the relationship between tinnitus and neurodegenerative diseases may be inflammation, which is common to many chronic disorders.