Impaired pre-attentive auditory processing in opioid dependence with and without benzodiazepine co-dependence revealed by combined magnetoencephalography and electroencephalography

Cognitive dysfunctions may be a significant factor in drug-seeking behavior, reducing the efficiency of rehabilitation in opioid dependence. Neurophysiological basis of these dysfunctions is poorly understood. 21 opioid-dependent patients and 15 healthy controls with no experience of illicit drugs were studied with simultaneous electroencephalography (EEG) and magnetoencephalography (MEG). Among opioid dependents 15 were benzodiazepine co-dependent. In a passive oddball paradigm, a train of 700-Hz standard tones (80%), presented to the left ear, was occasionally interrupted by infrequent deviants, which were either 600-Hz or 400-Hz pure tones or complex novel sounds. The auditory evoked potentials (AEP) and fields (AEF) were analyzed. The strength of the N1m dipoles was enhanced in patients with benzodiazepine co-dependence, but the latency of the response or the source location was not changed. A delay of mismatch negativity (MMN) response of novel tones in EEG, and delay of P3am response on the contralateral hemisphere to stimulated ear in MEG in opioid-dependent patients were observed. There were no differences in source locations or strengths of the dipoles for P1m, MMNm, and P3am determined using equivalent current dipoles. There were no group differences in EEG amplitude measures. In conclusion, our results suggest delayed pre-attentive auditory processing of novel information in opioid dependence. Benzodiazepine co-dependence modulated N1m response.