Figure 2.

Habituation of responses to the US. a, Habituating responses to the US on the behavioral level (pain ratings and SCR). For each subject, we calculated a regression with time as predictor and then compared the ensuing average regression coefficients of both groups. The bars in this graph thus represent the average regression coefficient of each group. The control group showed stronger habituation effects in the pain ratings (as reflected by a more negative average regression coefficient) than the naloxone group. In addition to this trend-level significant effect, the control group showed significantly stronger habituation effects in SCR to the US. b, Habituating BOLD responses to the US. The dorsal anterior cingulate cortex showed significantly stronger habituating responses to the US in the control group than in the naloxone group. The bar graph on the right shows peak voxel parameter estimates that reflect the strength of habituation (i.e., the more negative, the stronger the habituation). The parameter estimates show that the BOLD responses in the control group habituate strongly, whereas the naloxone group shows sustained BOLD responses in dorsal anterior cingulate cortex. The image is thresholded at p < 0.005 (uncorrected) for visualization purposes. *p < 0.05. Error bars indicate SEM.