Effect of the dopamine D2 antagonist sulpiride on event-related potentials and its relation to the law of initial value.

Effects of the dopamine antagonist sulpiride on event-related potentials (ERPs) were investigated during an auditory odd ball task in 18 healthy volunteers. Sulpiride (150 or 300 mg) or an inactive placebo was administered according to a completely randomized double-blind cross-over design. ERPs were recorded 1 h after medication was given. Sulpiride shortened the P200 latency for frequent stimuli, but tended to increase the N200 and P300 latencies for rare stimuli. Although on the whole sulpiride had no effect on the amplitudes of the ERP components in the subjects, it increased the P300 amplitudes in the low P300 amplitude subjects and decreased them in the high P300 amplitude subjects. This tendency for a bidirectional response was also found for the N100 and N200 amplitudes. A single administration of 150 or 300 mg sulpiride is considered to affect the ERP latencies and amplitudes in healthy subjects, the bidirectional response that takes place being dependent on the difference in the initial values. The results of this study are discussed in relation to the 'Law of initial value'.