Tinnitus, one of the world's most common hearing conditions, is known to impact a person's hearing and well-being, but can it also affect a person's cognitive performance? Many people with tinnitus think it can, based on various reports of concentration problems due to tinnitus.1 Researchers may think it can too, with published studies that found poorer cognitive performance in people with tinnitus than in those without tinnitus.2,3 Explanations for how tinnitus could affect cognition include cognitive load hypotheses where the increased effort of hearing and trying to suppress the tinnitus leaves fewer cognitive resources to complete a task at hand.
One of the challenges in determining the potential effect of tinnitus on cognition is the high prevalence of hearing impairment among people with tinnitus (estimated to about 90%4,5). Hearing impairment is independently associated with poorer cognitive performance, which can make it difficult to know whether poor cognitive performance among this population is the result of tinnitus, hearing impairment, or both.6-9 The lack of control for hearing loss in the previous literature investigating tinnitus and cognition9 that motivated us to investigate the relationships between tinnitus, cognition, and hearing in more detail.
We recruited 76 adult participants (23-66 years old) with high educational backgrounds; of these, 38 reported having chronic tinnitus and 38 didn't have tinnitus. Both groups were carefully matched for age, sex, and educational background, and each group included 19 individuals with normal hearing and 19 individuals with hearing impairment. We also screened the participants for symptoms of anxiety and depression, as these conditions are common among individuals with tinnitus1 and have been shown to negatively affect cognitive performance.10,11
All participants had their hearing thresholds measured at frequencies from 0.125 to 16 kHz. For the cognitive assessment, the participants completed a behavioral test called the n-back test, which is a visual test of working memory developed by Kirchner12 that is widely used in psychological research. It consists of several subtests, where N equals a non-negative integer (e.g. 0-back, 1-back, 2-back, and so on). In each subtest, the test person is presented with one symbol at a time (typically letters) and has to report whether the current symbol is identical to the symbol seen N presentations ago. In the 0-back condition, the task is to report when a specific symbol is presented (e.g., press the button every time you see “X,” do not press the button if you see a letter that is not “X”). With each increase of N, the task constitutes an increased load on the test person's working memory.
Surprisingly, we found that working memory capacity was not related to tinnitus but was related to hearing ability at very high frequencies (above 8 kHz) when controlling for anxiety, depression, and hearing status. This hearing at very high frequencies explained about 20 percent of the variance in working memory capacity in our participants.
We were not able to determine why tinnitus did not relate to cognitive performance but hearing at very high frequencies (above 8 kHz) did. A cognitive load hypothesis seems unlikely given the visual nature of our n-back task. Perhaps more likely is a common cause hypothesis, which suggests that another factor is acting as a common cause of deterioration of cognitive performance and hearing thresholds. Factors suggested in such a relationship include microvascular insufficiency and oxidative stress.6 Another possible explanation could be in line with a cascade hypothesis, suggesting the decreased electrical stimulation of the brain due to sensory deprivation could lead to decreased total brain volume.6
From a clinical perspective, we think our results have implications for how audiologists should assess hearing in patients who report cognitive difficulties. Audiologists typically measure hearing at frequencies of 0.125 to 8 kHz. This range of test frequencies would miss hearing impairments of the type found to be associated with working memory capacity in our study. A relationship between hearing at very high frequencies (above 8 kHz) and cognitive performance could also have implications for auditory rehabilitation. In this regard, hearing aids would need to be able to amplify sounds above 8 kHz if they are to contribute to any relationship between better hearing at these very high frequencies (above 8 kHz) and better cognitive performance.
Finally, while our study found no relationship between tinnitus and cognitive performance, its findings also highlight the need for a thorough hearing examination among tinnitus patients for at least two reasons. First, these patients have hearing impairments.4,5 Second, it is common for patients with tinnitus to associate hearing-related difficulties with their tinnitus rather than with their hearing impairment.13 In addition, our group has reported four studies indicating that hearing status plays a greater role than the presence of tinnitus in cognitive performances.8,14-16 Despite some clinical guidelines listing hearing examination as optional in tinnitus management,17 we argue that there is sufficient evidence to require a thorough hearing examination for all patients with tinnitus. Optimally, such examination would also include measurement of hearing thresholds above 8 kHz.
Article originally appeared on The Hearing Journal