Recent studies have begun to elucidate the neural correlates of evidence accumulation in perceptual decision making. Few of them have used a combined modeling-electrophysiological approach to studying evidence accumulation. We introduce a novel multivariate approach to EEG analysis with which we can perform a comprehensive search for neural correlates of dynamics predicted by the drift diffusion model. We show that the dynamics of evidence accumulation are correlated with decreases in the 4-9 Hz theta band over the course of a trial. The rate of decrease in this band correlates with individual differences in fitted drift diffusion model parameters.