The effects of increasing and decreasing dopamine on inhibition of return: a psychopharmacological investigation.

Inhibition of Return (IOR) is the phenomenon of being slower to re-attend to previously attended locations, and is thought to improve the efficiency of attention. Previous studies of dopaminergic disorders indicate that excessive or insufficient dopamine signaling in the striatum of the brain reduces IOR magnitude. However, there have been no studies of the direct effects of dopamine depletion on IOR in healthy individuals, or that have compared the effect of dopamine increases and decreases within the same population. Therefore, in the present study, we administered a selective dopamine-2 receptor (D2R) agonist and antagonist to the same healthy participants (cabergoline and amisulpride, respectively) and measured IOR. We further investigated the effects of dopamine manipulation on the underlying cognitive processes of IOR using event-related potentials. Both manipulations reduced the IOR effect relative to placebo, consistent with a non-linear relationship between dopamine and IOR. Given the D2R selectivity of both drugs and the accompanying changes in eye-blink rate, these effects are likely driven by primarily striatal dopamine, potentially reflecting frontostriatal modulation of the balance between attentional flexibility and stability.