Auditory event-related potentials in methadone substituted opiate users

The effects of methadone maintenance treatment (MMT) on neurophysiological function are unclear. Using an auditory oddball paradigm, event-related potential (ERP) amplitudes and latencies were measured in 32 patients undertaking MMT, 17 opiate users who were addicted but not receiving substitution treatment and 25 healthy control subjects. Compared with healthy control subjects, the MMT and opiate user groups showed an increased P200 amplitude in response to target stimuli. The opiate user group also exhibited a decreased amplitude and an increased latency of N200, and a greater number of task-related errors than either healthy control subjects or patients undertaking MMT. There were no significant group differences in the P300 amplitude. However, it is noteworthy that the frontal P300 amplitude of the MMT group was greater than that of opiate users or healthy controls. Our findings suggest that altered sensory information processing associated with a history of opiate use remains in patients undertaking MMT. However, there are less marked ERP abnormalities in those receiving MMT than in active opiate users. The deficits in information processing associated with illicit opiate use are likely to be reduced during MMT.