Event-related brain potential evidence of spared knowledge in Alzheimer's disease

The authors recorded event-related brain potentials (ERPs) to picture prime s and word targets (picture-name verification task) in patients with Alzhei mer's disease (AD) and in elderly and young participants. N400 was more neg ative to words that did not match pictures than to words that did match pic tures in all groups; In the young, this effect was significant at all scalp sites; in the elderly, it was only at central-parietal sites; and in AD pa tients, it was limited to right central-parietal sites. Among AD patients p retested with a confrontation-naming task to identify pictures they could n ot name, neither the N400 priming effect nor its scalp distribution was aff ected by ability to name pictures correctly. This ERP evidence of spared kn owledge of these items was complemented by 80% performance accuracy. Thus, although the name of an item may be inaccessible in confrontation naming, N 400 shows that knowledge is intact enough to prime cortical responses.