Event-related potential repetition effect in Alzheimer's patients: Multiple repetition priming with pictures

The most notable symptom in probable Alzheimer's disease (PAD) is a profound deficit on direct or explicit memory tasks. In many cases these same patients show performance similar to normal controls on indirect or implicit memory tasks. During indirect testing, recent studies have shown that many PAD subjects have an intact event-related potential (ERP) repetition effect, which is thought to index indirect memory functioning. The present study was designed to test the effect of multiple repetitions on the ERPs of PAD patients. ERPs were recorded from 8 subjects with PAD,;8 elderly and 16 young healthy controls. Subjects were asked to make speeded but accurate choice responses to infrequently occurring animal pictures and frequently occurring nonanimal pictures. Stimuli were presented in four sets of three blocks of trials. Half of the nonanimal items from the first block of each set were repeated in the subsequent two blocks of trials along with new or foil nonanimal pictures, resulting in three presentations of these stimuli. For the ERPs, all three groups of subjects showed activity that was more positive to old than to new items, with no additional enhancement to the third presentation The ERP enhancement to repeated items was associated with reaction time (RT) facilitation which, in contrast to the ERPs, increased with a third presentation in the two older groups, but not in the young group. These results suggest that ERP and RT repetition priming effects are relatively intact in subjects who are aging normally and in those with a diagnosis of ''mild'' Alzheimer's disease.