Title : Inhibitory oculomotor control in cannabis and psychostimulant dependents
Abstract:
The loss of inhibitory control (IC) has been closely associated with addictive behaviors. The IC is a cognitive process that has considerably influence in the behavioral regulation. Alterations in IC in patients with substance use disorder have been identified mainly in inhibitory motor and interference control; however, the results are not always conclusive. The oculomotor inhibitory control is a type of inhibitory control related to the same brain areas where most drugs (including cannabis and psychostimulants) take place of action, predominantly in the prefrontal cortex and basal ganglia that are a neurobiological substrate of IC. Oculomotor tasks have been considered as a sensitive tool to detect inhibitory control alteration, because participants must suppress the automatic response, they not require complex cognitive processes and its activation time is quick. Therefore, the aim of this study was to determinate the presence of deficit in oculomotor inhibition in chronic cannabis consumers and psychostimulant dependents. Two experiments were carried out. The same pro-saccade and anti-saccade tasks under the overlap and gap conditions were applied with an infrared eye tracker in both experiments. In the first one, 39 psychostimulant dependents (GS) and 22 control persons (CG) participated. All dependents were inpatients in abstinence. The results revealed that GS showed significantly higher error rates under the pro- and anti- gap conditions; higher rates of express saccades under the pro- and anti- overlap condition, and anticipatory saccades rates than GC in all conditions. In the second experiment, 25 chronic cannabis users (THCG) and 25 control group participants (CG) were recruited. Inclusion criteria for cannabis users were consuming at least 4 times a week in the past year and having at least 12 hours of abstinence before the assessment. The THCG committed a greater number of anticipatory prosaccades in the gap condition than CG. The results point out that the inhibitory deficit in psychostimulant and cannabis users is associated to alterations in the oculomotor inhibitory system due to toxic effect of drugs mainly on the basal ganglia. Apparently, the psychostimulant use produces a greater deficit in oculomotor inhibitory control than the cannabis use. High anticipatory saccades rates and express saccades are related with impulsivity. Similar data have been reported in patients with Tourette’s syndrome, whose main symptom is motor impulsivity and compromise the basal ganglia and frontal cortex. In addition, in cannabis users the inhibitory oculomotor deficit is evident when the task turns more complex (gap condition), i.e. when condition is given without contextual clues.
