Numerous studies have brought forward evidence for a prominent role of dopamine in planning. Because the direction of the effect of dopamine in planning is ambiguous this issue is in need of further investigation. In this between-subject, placebo-controlled study, administration of high doses (800 mg) of the dopamine D2/D3 antagonist sulpiride was combined with genetic analysis of the striatal dopamine D2 receptor. The One-Touch Stockings of Cambridge (OTSOC), a modified version of the original

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... Tower of London task was used to measure planning in a sample of 77 healthy male volunteers. As hypothesized we found impaired planning performance at the OTSOC following sulpiride administration. We did not find modulatory effects concerning striatal dopamine D2 receptor density. Our findings suggest that sulpiride might not predominantly act on striatal dopamine D2/D3. The exhibited sulpiride effect could also be the consequence of cortical dopamine D2/D3 receptor blockade. Furthermore, our findings question the proposed prominent role of dopamine D2 receptors in planning. Hence a possible crucial role of dopamine D3 receptors in planning should be investigated in future studies.