The left plot shows the average amplitude of local field potentials (below 12 Hz) for the 3-sec period before the trials for data from 6 rats. The right plot shows the ratios of amplitude on post-error and post-correct trials. Amplitudes were significantly larger on post-error trials (paired t-test: t=-4.23, df=5, p<0.01). Ratios for local fields from all 6 rats were larger than 1. The mean ratio is depicted by the + symbol.