Interacting effects of frontal lobe neuroanatomy and working memory capacity to older listeners' speech recognition in noise

Many older adults are struggling with understanding spoken language, particularly when background noise interferes with comprehension. In the present study, we investigated a potential interaction between two wellknown factors associated with greater speech-in-noise (SiN) reception thresholds in older adults, namely a) lower working memory capacity and b) age-related structural decline of frontal lobe regions. In a sample of older adults (N = 25) and younger controls (N = 13) with normal pure-tone thresholds, SiN reception thresholds and working memory capacity were assessed. Furthermore, T1-weighted structural MRimages were recorded to analyze neuroanatomical traits (i.e., cortical thickness (CT) and cortical surface area (CSA)) of the cortex. As expected, the older group showed greater SiN reception thresholds compared to the younger group. We also found consistent age-related atrophy (i.e., lower CT) in brain regions associated with SiN recognition, namely the superior temporal lobe bilaterally, the right inferior frontal and precentral gyrus, as well as the left superior frontal gyrus. Those older participants with greater atrophy in these brain regions showed greater SiN reception thresholds. Interestingly, the association between CT in the left superior frontal gyrus and SiN reception thresholds was moderated by individual working memory capacity. Older adults with greater working memory capacity benefitted more strongly from thicker frontal lobe regions leading to better SiN recognition. Overall, our results fit well into the literature showing that age-related structural decline in auditory- and cognition-related brain areas is associated with greater SiN reception thresholds in older adults. However, we highlight that this association changes as a function of individual working memory capacity. We therefore believe that future interventions to improve SiN recognition in older adults should take into account the role of the frontal lobe as well as individual working memory capacity.

Automated summary

This study investigated the relationship between working memory capacity, age-related structural decline in the brain, and speech-in-noise reception thresholds in older adults. The results showed that older adults with greater age-related atrophy in specific brain regions had higher speech-in-noise reception thresholds. Moreover, individual working memory capacity moderated the association between certain brain regions and speech-in-noise reception thresholds.