Inter-trial variability in postural control and brain activation: Effects of previous opiate abuse.

There is an abundant literature demonstrating the superiority of inter-trial variability (ITV) of reaction time over mean reaction time in the early identification of subtle cognitive processing decrements. The present study extends these ideas by examining brain activation and postural control ITV among participants with versus without a history of chronic opiate abuse. Participants enrolled in opiate abuse (n = 82) and control (n = 112) groups completed tasks that challenged selective attention and balance. During the respective tasks, the inter-trial variabilities in frontal P300a electroencephalographic responses and sway strategy scores outperformed their mean levels in differentiating the groups. The relevance of several potential alternative explanations for the differences, including premorbid conduct disorder and comorbid alcohol abuse, depression, and methadone use, was discounted via simultaneous or post hoc analyses. It appears that chronic opiate abuse has adverse CNS effects that persist into the protracted abstinence period. These effects alter the temporal stability of its response to external and internal stimuli.