Analysis of pattern-reversal visual evoked-potential topography: replicability in normal subjects and comparisons with Alzheimer's disease.

This paper reports two studies using multivariate analysis to aid the interpretation of cross-coherence of multiple electrode sites in evoked potential responses. In the first study, the replicability of principal components and multidimensional scaling was evaluated by applying both methods to pattern-reversal visual evoked potentials recorded from 28 scalp sites in two subgroups of sex- and age-matched healthy subjects, and then comparing the results. Four dimensions replicated in the two initial multidimensional scaling solutions and appeared to reflect differences in: 1) anterior versus posterior scalp areas, 2) laterality, 3) separation of frontal and occipital sites from other scalp regions, and 4) proximal versus distal placements. The initial principal components did not match well in the two groups, but rotation to congruence improved their replicability and ultimately yielded axes similar to those of the multidimensional scaling dimensions. In the second study, Alzheimer's disease and sex- and age-matched control subjects were evaluated. The four axes identified were the same as those described above, but after the solutions were rotated to align them, the group differences appeared negligible. Examination of the components and dimensions from both studies showed some consistent departures from being merely reflectors of site location, and the apparently visual dimension appeared clearly in all four groups. Judged on the basis of initial interpretability and replicability of the solutions, the results suggest that multidimensional scaling, with appropriate transformation, may provide an effective tool for analyzing pattern-reversal visual evoked-potential topography.