This analysis showed a drug × genotype interaction [ F 1,60) = 9.2; p =.004], with Met-COMT subjects outperforming Val-COMT subjects in the placebo groups (p =.024) and Val-COMT subjects tending to outperform Met-COMT subjects in the tolcapone groups (p =.053).
Because of the small number of Met homozygous subjects, Met/Met and Met/Val subjects were grouped together.
In the placebo group, Met-COMT subjects outperformed Val-COMT subjects on the 2- back, and they were more risk averse.
On placebo, Met-COMT subjects out-performed Val-COMT subjects (p =.006), but in the tolcapone group, this difference was reversed such that Val-COMT subjects outperformed Met-COMT subjects (p =.022); tolcapone significantly impaired performance in Met-COMT subjects (p =.019) and improved it in Val-COMT subjects (p =.007).
We found a trend-level RT × genotype interaction [ F(1.86,98.7) = 2.79, p =.070], with Met-COMT subjects reacting faster than Val-COMT subjects (p =.049).
On placebo, Met-COMT subjects reacted faster than Val-COMT subjects on the 2-back (p =.046) and 3-back (p =.039); no genotype differences in RT were seen for subjects on tolcapone.
Our findings that, on placebo, Met-COMT subjects performed better than Val-COMT subjects at the 2-back replicates the result of one large study (15,40) but many other studies (e.g., Blanchard et al).
Tolcapone made Met-COMT subjects less risk averse but Val-COMT subjects more so.
Tolcapone had opposite effects in the two genotype groups: it worsened N-back performance in Met-COMT subjects but enhanced it in Val-COMT subjects.
After whole-body CT for attenuation correction and intravenous bolus injection of MET, the subjects were scanned from the parietal to the groin.
