Effects of the dopamine-related drug bromocriptine on event-related potentials and its relation to the law of initial value.

Effects of the dopamine-related drug bromocriptine (BCT) on event-related potentials (ERP) were investigated in 18 healthy volunteers. Bromocriptine 2.5 mg or an inactive placebo was administered according to a completely randomized double-blind, cross-over design. The ERP were recorded 3 h after medication was given. Although BCT prolonged the P300 latency, it had no effect on the amplitudes of the ERP components as a whole. Bromocriptine increased the latencies of N100, P200 and P300 in the respective short-latency subject group, and decreased the latency of N200 in the long-latency subject group. It increased the amplitude of N200 in the low-amplitude subject group. It was concluded that the prolongation of P300 latency as a whole and the different responses that take place are dependent on the initial values and were recognized in the effect of a single administration of BCT 2.5 mg. The results of this study are discussed in relation to the law of initial value.