Abstract
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 Alzheimer's 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's disease.
Highlights
Mild cognitive impairment (MCI) is a clinical condition that characterizes elderly individuals with an episodic memory impairment that is more severe than in normal aging, while other cognitive functions are relatively normal (Petersen et al, 1999; Ritchie and Touchon, 2000; reviewed in Collie and Maruff, 2000)
On the Mini-Mental State Exam MCI subjects scored significantly lower than controls
Individual MCI subjects performed within 2 standard deviations from standard published means on all non-memory tasks, with the exception of one subject who performed in the severe impairment range on the Boston Naming Test
Summary
Mild cognitive impairment (MCI) is a clinical condition that characterizes elderly individuals with an episodic memory impairment that is more severe than in normal aging, while other cognitive functions are relatively normal (Petersen et al, 1999; Ritchie and Touchon, 2000; reviewed in Collie and Maruff, 2000). Alzheimer’s disease has a long preclinical period, lasting years to decades, when b-amyloid plaques and neurofibrillary tangles accumulate in the brain without appreciable clinical abnormalities (Morrison and Hof, 1997; Celsis, 2000; Elias et al, 2000; Small et al, 2000). The long preclinical period of Alzheimer’s disease coupled with the observation that many MCI patients convert to Alzheimer’s disease within a few years implies that many MCI patients have neuropathology similar to Alzheimer’s disease. Consistent with this notion, Price and Morris, 1999 described extensive b-amyloid plaques in both nondemented and mildly demented subjects. A recent study reported that MCI subjects had neuropathological findings characteristic of Alzheimer’s disease (Morris et al, 2001)
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