Differences in EEG oscillations between normal aging and mild cognitive impairment during semantic memory retrieval

Abstract

Semantic memory remains relatively stable with normal cognitive aging and declines in early stages of neurodegenerative disease. We measured electroencephalography (EEG) oscillatory correlates of semantic memory retrieval to examine the effects of normal and pathological aging. Twenty-nine cognitively healthy young adults (YA), 22 cognitively healthy aging adults (HA), and 20 patients with mild cognitive impairment (MCI) completed a semantic memory retrieval task with concurrent EEG recording in which they judged whether two words (features of objects) led to retrieval of an object (retrieval) or not (non-retrieval). Event-related power changes contrasting the two conditions (retrieval vs. non-retrieval) within theta, alpha, low-beta, and high-beta EEG frequency bands were analyzed across time to examine normal aging (YA versus HA) and pathological aging effects (HA versus MCI). Though no behavioral differences between the cognitively healthy groups were observed, we found later theta and alpha power differences between conditions only in YA, and a high-beta power difference between conditions only in HA. For pathological aging effects, we found reduced accuracy in MCI. While we found different EEG patterns of early beta power differences between conditions in MCI compared to HA, a low-beta power difference between conditions was found only in HA. We conclude that the aging brain relies on faster (beta) oscillations during the semantic memory task. With pathological aging, retrieval accuracy declines and patterns of beta oscillation changes. The findings improve understanding on age-related neural mechanisms underlying semantic memory and have implications for early detection of pathological aging.