Neurophysiological signatures underlying preserved lexical-semantic proficiency in healthy aging

Although semantic cognition remains behaviorally stable with age, neuroimaging studies report age-related alterations in response to semantic context. To address these inconsistent findings, we combined behavioral and magnetoencephalography (MEG) measures and examined the neural mechanisms underlying lexical-semantic processing in healthy aging. Forty-six Finnish-speaking adults across younger (22 - 32 years) and older (62 - 69 years) cohorts performed a semantic congruency judgment task on word pairs. Both age groups performed the task with high accuracy, with older adults responding faster than younger. While task performance was retained in older adults, MEG revealed a shift in the neural activation patterns with advancing age. Younger participants exhibited the canonical N400 effect in the left temporal cortex 300 - 400 ms post-stimulus, followed by a late semantic effect, whereas older adults showed less pronounced congruency effects, and the activation distribution was shifted toward frontal and bilateral regions. Despite the absence of the canonical N400 effect in older participants, multivariate time-resolved decoding demonstrated that the congruency effect was decodable from the MEG activation patterns in both groups from ~300 ms post-stimulus, indicating preserved sensitivity to congruency with age. Decoding performance further correlated with response times, suggesting that greater neural separation between semantic concepts, indicated by higher decodability, is associated with rapid decision-making. Critically, age groups were distinguishable based on their neural responses 300 - 800 ms post-stimulus, indicating a functional reorganization of semantic processing in older adults. Overall, our findings suggest that healthy aging involves a reconfiguration of neural systems associated with preserved semantic proficiency, despite broader age-related cognitive changes.