Semantic and Phonological Brain Networks in Older Adults: A Systematic Scoping Review

Background/Objectives: Despite many neurobiological models of semantics and phonology, there is no consensus regarding their functional organization. Specifically, there is considerable debate concerning the precise functional roles of the left inferior frontal gyrus and inferior parietal lobe, where these two networks may overlap. Meta-analyses addressing this topic have focused on neurologically intact young adults, yet theories of cognitive aging suggest older adults may exhibit a different distribution of their language networks. This scoping review specifically explores the interplay between semantic and phonological neural networks in older adults. Methods: Following the PRISMA extension guidelines, we carried out a systematic search to identify relevant primary research. Thirty-seven studies were included, representing a range of populations (e.g., neurologically intact older adults, post-stroke aphasia), methodologies (e.g., task-based functional magnetic resonance imaging, lesion symptom mapping), and sample sizes from 11 to 1231 participants. Results: Based on the number of studies identifying relationships with a given region, we found that regions potentially specialized for semantics or phonology and those potentially subserving both domains are largely consistent with networks derived from meta-analyses of younger adults. However, we found subtle differences between older and younger adults. Conclusions: Our results are generally compatible with the CRUNCH or de-differentiation perspectives of cognitive aging. In our characterization of the literature related to the semantic and phonological networks of older adults, we did not see a pattern consistent with the HAROLD or PASA models, though our findings were limited by methodological decisions. Our work suggests that future complementary activation- and lesion-based meta-analyses are warranted to more precisely delineate the semantic and phonological networks in older adults.