Age-Related Differences In The Influence Of Task-Irrelevant Information On The Neural Bases Of Phonological And Semantic Processes

Although aging is often associated with cognitive decline, there is considerable variability among individuals and across domains of cognition. Within language, several indicators of semantic processing show stability throughout the lifespan. However, older adults have increased difficulty with phonological aspects of language, especially in language production. While these behavioral patterns are established, the neurobiology associated with these behaviors are less clear. Previously we have shown that, older adults were slower and less accurate in phonological compared to semantic decisions, and that older adults didnt exhibit brain-behavior relationships. In the present study, we examined phonological and semantic processes in the presence of task-irrelevant information. Older and younger adults made phonological and semantic decisions about pictures in the presence of either phonologically-related or semantically-related words, which were unrelated to the task. Behavioral results indicated that overall older adults had slower reaction times and lower accuracy compared to younger adults, and that all adults were less efficient when making phonological compared to semantic decisions. Patterns of brain activation for the semantic condition showed that all adults engaged typical left-hemisphere language regions, and that this activation was positively correlated with efficiency. In contrast, the phonological condition elicited activation in bilateral precuneus and cingulate, but only younger adults showed a significant relationship between activation and efficiency. Our results suggest that the relationship between behavior and neural activation when processing phonological information declines with age, but that the core semantic system continues to be engaged throughout the lifespan, even in the presence of task-irrelevant information.