Neural evidence for phonologically based language production deficits in older adults: An fMRI investigation of age-related differences in picture-word interference

Introduction: Older adults often show declines in phonological aspects of language production, particularly for low-frequency words, but maintain strong semantic systems. However, there are different theories about the mechanism that may underlie such age-related differences in language (e.g., age-related declines in transmission of activation or inhibition). Methods: This study used fMRI to investigate whether age-related differences in language production are associated with transmission deficits or inhibition deficits. We used the picture-word interference paradigm to examine age-related differences in picture naming as a function of both target frequency and the relationship between the target picture and distractor word. Results: We found that the presence of a categorically related distractor led to greater semantic elaboration by older adults compared to younger adults, as evidenced by older adults’ increased recruitment of regions including the left middle frontal gyrus and bilateral precuneus. When presented with a phonologically related distractor, patterns of neural activation are consistent with previously observed age deficits in phonological processing, including age-related reductions in the recruitment of regions such as the left middle temporal gyrus and right supramarginal gyrus. Lastly, older, but not younger, adults show increased brain activation of the pre- and postcentral gyri as a function of decreasing target frequency when target pictures are paired with a phonological distractor, suggesting that cuing the phonology of the target disproportionately aids production of low-frequency items. Conclusions: Overall, this pattern of results is generally consistent with the transmission deficit hypothesis, illustrating that links within the phonological system, but not the semantic system, are weakened with age.