Auditory event-related potentials during target detection are abnormal in mild cognitive impairment

Objective: To define brain activity and behavioral changes in mild cognitive impairment (MCI), an isolated memory deficit in the elderly that is a major risk factor for Alzheimerʹs disease. Methods: Brain potentials and reaction time were examined in elderly controls (n=12) and MCI (n=15) using a target detection paradigm. Subjects listened to a sequence of tones and responded to high-pitched target tones (P=0.20) that were randomly mixed with low-pitched tones (P=0.80). Measures were a pre-stimulus readiness potential (RP), post-stimulus potentials (P50, N100, P200, N200, P300), and reaction time. Results: Accuracy was equivalent between groups, but there was a trend for longer reaction times in MCI (P=0.08). Two potentials differed between groups: (1) P50 amplitude and latency were significantly increased in MCI, and (2) P300 latency was significantly longer in MCI. Results from two MCI subjects that converted to Alzheimerʹs disease are also discussed. Conclusions: Brain potentials in MCI subjects during target detection have certain features similar to healthy aging (RP, N100, P200, N200), and other features similar to Alzheimerʹs disease (delayed P300 latency, slower reaction time). P50 differences in MCI may reflect pathophysiological changes in the modulation of auditory cortex by association cortical regions having neuropathological changes in early Alzheimerʹs disease.