Response inhibition and psychomotor speed during methadone maintenance: impact of treatment duration, dose, and sleep deprivation.

Background: In opiate-dependent individuals, abstinence results in deficits in cognitive functioning, which may be exacerbated by medication-associated sleep disruption.

Method: To assess cognitive function and the influence of sleep deprivation (SD), 14 healthy control (HC) and 22 methadone maintained (MM) participants completed the continuous performance task (CPT) after a baseline night, a night of total SD, and two recovery sleep nights. The digit symbol substitution task (DSST) was administered at bedtime and in the morning. Secondary analyses separated MM participants into short- (< 12 months; n=8) and long-term (≥ 12 months; n=14) treatment duration groups, and into low- (< 80 mg; n=9) and high-dose (≥ 80 mg; n=13) groups.

Results: Linear mixed model ANOVAs revealed that there was no effect of SD. Across all days MM participants had more errors of omission, fewer correct responses, and slower reaction times (RTs) on the CPT, and fewer accurate substitutions on the evening and morning DSST. Short-term MM participants exhibited slower RTs on the CPT, and fewer correct substitutions on the evening DSST compared to long-term MM participants. Low-dose MM participants had slower RTs on the CPT than HCs and high-dose MM participants.

Conclusion: These data demonstrate that methadone-maintained individuals exhibit poorer performance on tasks of psychomotor speed and selective attention/impulsivity, but with longer-term treatment, performance appears to return toward control levels. Furthermore, while one day of SD was enough to alter subjective reports of sleep quality, cognitive function may be more resilient.