Latency variability of the components of auditory event-related potentials to infrequent stimuli in aging, Alzheimer-type dementia, and depression.

Auditory event-related potentials (ERPs) were investigated in 15 demented (12 presumed Alzheimer's, 3 cerebrovascular), 8 depressed, and 15 normal older, and 12 normal young, subjects. Both latencies from conventional averages and latency variability measures from single trials were derived for the N100, P200, N200, and P300 components of the ERP recorded from Fz, Cz and Pz scalp placements in a task requiring detection of an infrequent target tone among a series of frequent non-target tones. The P300 component most consistently separated the groups. Demented subjects had longer P300 latencies and greater P300 latency variability than both control groups and the depressed group. Age differences were observed for P300 latency, but not for P300 latency variability. Amplitudes were not significantly different among the groups. Reaction times (RTs) to the targets were longest for the demented subjects and shortest for the young controls, with the depressed and normal older control groups falling in between. Correlations between RT and P300 latency from single trials did not differentiate the groups. Using regression analysis to evaluate the deviation of P300 latency and latency variability for the patients from the predicted values for normal controls, no misclassifications of depressed patients occurred, but only 27% of the demented individuals were correctly classified using P300 variability, and 13% using P300 latency. These findings indicate that ERP measures using the 'oddball' target detection paradigm were useful in describing group differences, but were not sufficiently sensitive to be used in differentiating demented persons on an individual basis for clinical diagnosis.