Effects of the GABA mimetic drug, sodium valproate, on event-related potentials and its relation to the law of initial value.

The effects of gamma-aminobutyric acid (GABA) mimetic drug sodium valproate (VPA) on event-related potentials (ERPs) were investigated in 18 healthy volunteers during an auditory odd ball task. VPA (200 or 400 mg) or an inactive placebo was administered according to a completely randomized double-blind, cross-over design. ERPs were recorded one hour after medication was given. VPA did not affect the latencies of N100, P200, N200 and P300. Although on the whole VPA had no effect on the amplitudes of the ERP components in the subjects, it increased the P300 amplitude in the low P300 amplitude subjects and decreased it in the high P300 amplitude subjects. This tendency toward a bidirectional response was also seen in the P200 and N200 amplitudes. It was concluded that the response which takes place being dependent on the difference in the initial values was recognized on the effect of a single administration of 200 or 400 mg VPA to ERPs. The results of this study are discussed, especially in relation to the law of initial value.