Substance-related and addictive disorders have been strongly linked to inhibitory control impairment. However, inhibitory deficits in this class of psychiatric disorders have been tested almost exclusively with measures of inhibition of motor, overt behavior. Here, instead, we investigated inhibitory deficits in these disorders by assessing the integrity of inhibitory control over internal, covert responses. Two groups of patients with alcohol and drug addiction and a control group of healthy individuals were administered a retrieval-practice paradigm assessing inhibition of competing memories. All groups showed comparable beneficial effects of retrieval practice. In contrast, successful suppression of competing memories was achieved by the control group only. This indicates that the deficit in clinical groups can be ascribed to an impairment in inhibitory control over memory retrieval rather than to a general memory impairment. In conclusion, inhibitory deficits in addiction are more widespread than previously shown, as they encompass memory control mechanisms.
