Impact of Age-Related Hearing Loss on Brain Connectivity and Cognitive Performance: A Systematic Review.

Every included study was observational, either cohort or case-control, so the review can describe associations between hearing loss, connectivity and cognition but cannot say whether one causes another. The authors state this themselves. The studies were highly varied in which cognitive tests they used, how they measured connectivity and which brain regions they examined, and the authors say this prevents a single consistent picture from being drawn. The authors rated study quality but deliberately did not let those ratings influence how they interpreted the results, because so few studies met the criteria. Many studies reported only whether a result was statistically significant and gave no effect size, so how large the connectivity differences actually were is often unknown. Seven of the 25 reported no effect size. Two of the studies had no control group at all, and two pairs of studies appear to have used the same participants, so these are not 25 independent samples. Effective connectivity, the analysis that can speak to direction of influence between brain regions, was examined in only two of the 25 studies. Individual samples were small, often a few dozen people, and hearing loss in most studies was mild.

The authors received no financial support for the research or writing, and declared no conflicts of interest.

Do not read this as showing that hearing loss damages the brain or causes dementia. The review itself states that it reports associations only, that most of the underlying evidence is cross-sectional, and that it does not address causality. No study here tested hearing aids, auditory training, cognitive rehabilitation or any other treatment, so nothing in it shows that treating hearing loss, or changing brain connectivity, prevents cognitive decline.