Event-related brain potentials (ERPs) and performance measures will be recorded from patients with probable Alzheimer's disease (PAD), and age- matched normal controls. The main thrust of the proposal is to assess performance on explicit and implicit tests of memory in carefully controlled designs, in an attempt to uncover the physiological underpinnings of memory deficiencies in PAD reported in the behavioral literature. Three experiments are proposed: 1) the first asks the question how do PAD subjects differ from age-matched controls (behaviorally and with respect to ERPs) in the ways in which they process pictorial and lexical input on-line, and the ways in which they remember and retrieve such input during implicit (fragment completion) and explicit (recognition) testing; 2) the second is aimed at assessing the adequacy of encoding operations at study. Orienting task will be used to manipulate encoding activity. ERP activity at study will be computed, separately by orienting task, as a function of subsequent stem completion (implicit) and cued recall (explicit) performance. This activity (i.e., the ERP """"""""memory effect"""""""") is expected to differ between the groups as a function of differences in encoding operations; 3) the third seeks to determine if the ERP and behavioral repetition effect will be modulated by the number of repetitions of an item (i.e., its """"""""memory strength"""""""") similarly in PAD and age-matched control subjects. In constrast to the previous experiment, memory will only be tested implicitly, and the focus is on retention. In general, it is also expected that the amplitude of the ERP old/new repetition effect will reflect the magnitude of priming during on-line and delayed memory tasks. ERPs will be recorded from several scalp placements in order to determine whether scalp distributions and, by implication, their intracranial generators, differ systematically between the groups. The data will be relevant to age-related pathological changes in memory function, and their physiological underpinnings.
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