AGE-RELATED ERP MEASURES IN ALZHEIMERS DISEASE

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The major focus of this proposal is on a better understanding of auditory attentional mechanisms in probable Alzheimer's disease (PAD). In addition, to assess early, pre-attentive, mainly automatic information processing and short-term storage of auditory information in PAD we will record the mismatch negativity (MMN), which is an event-related brain potential (ERP) component reflecting the short-term storage of auditory information outside the focus of awareness. To assess the more controlled aspects of auditory attention, we will use selective or directed attention paradigms that manipulate the stimulus features that must be attended. These paradigms give rise to early and late ERP components (processing negativities; PN) that reflect, respectively, selection of stimuli based on the attributes that characterize stimuli in the attended channel, and selective rehearsal of these attributes. Neuropathological data suggest that primary auditory cortex, upon which MMN generation depends, is intact in PAD. By contrast, auditory, temporo-parietal and frontal cortical association areas (comprising an attentional network), upon which intact early and late ERP signs of selective attention depend, may be damaged in PAD. These data lead to the expectation that ERP signs of pre-attentive auditory mechanisms may be relatively intact in mild and moderately demented patients, whereas ERP signs of selective attention will vary with disease severity. ERPs will be recorded from 30 scalp placements in order to determine whether MMN and PN component scalp distributions and, by implication, their underlying neural sources, differ systematically between the patient and control groups and/or conditions of the different experiments. The data will be relevant to preattentive processing related to sensory memory, to selective attention based on complex features, age-related pathological changes in these mechanisms, and their physiological underpinnings.