Objective: The aim of this functional magnetic resonance imaging (fMRI) study was to investigate reward-related brain activity in satiated overweight and healthy-weight participants in response to high-calorie palatable food pictures, when viewing the pictures without prior instructions (called unbiased viewing) versus imagining the taste of the shown pictures (called taste imagination). We predicted that neural activation in brain reward regions would be greater in overweight participants than in healthy-weight ones and that this difference between groups would be strongest during unbiased viewing. Method: Neural activation was measured using fMRI in 14 overweight (mean body mass index (BMI): 29.8 kg m À2 ) and 15 healthy-weight (mean BMI: 21.1 kg m À2 ) participants who were satiated, in response to palatable and unpalatable highcalorie and low-calorie food pictures, presented in an event-related design during two conditions: unbiased viewing (no prior instructions) versus taste imagination. Results: A group  condition interaction was found in 14 brain regions involved in food reward processing during the presentation of high-calorie palatable food stimuli. During the taste imagination condition, neural activation in these regions was greater in the overweight participants than in the healthy-weight ones. Contrary to our expectations, the opposite pattern was observed during unbiased viewing: activation in reward regions in the overweight participants was reduced compared with the healthy-weight ones. In all brain reward regions except for the left amygdala, the group  condition interaction was specific to high-calorie palatable food stimuli. Conclusion: Greater reward activity in the overweight participants compared with the control group when imagining taste may represent an increased reward response induced by high-calorie palatable food. During unbiased viewing, reduced reward activation in the overweight participants compared with those with a healthy weight may reflect avoidance of high-calorie palatable food stimuli. Taken together, this pattern of activation may reflect ambivalence in the overweight group between desire for (in the taste imagination condition) and avoidance of (in the unbiased viewing condition) high-calorie palatable food stimuli.

Cue reactivity and craving can be influenced by cue exposure with response prevention (CERP). This study investigated the neural correlates of CERP using functional magnetic resonance imaging, while participants smelled chocolate (17 participants) or a control object (17 participants). CERP was interrupted by 7 scanning sequences measuring the brain response to neutral and chocolate pictures. Chocolate craving was hypothesized to be mirrored by activation in brain reward regions. As expected, control group craving remained similar throughout the session. A short exposure (30 min) increased chocolate craving in the experimental group, which was mirrored by significant group differences in activation in brain reward regions. Unexpectedly, a long exposure (60 min) did not lead to craving extinction in the experimental group, although craving started to decrease at this point. On a neural level, however, activation in regions of interest in the experimental group seemed to have extinguished after the long exposure, as activation levels returned to or fell below control group levels. These results indicate that brain reward activation during CERP is linked to craving, at least for a short exposure. Regarding a longer exposure, the decline in brain reward activation in the experimental group may be a precursor of a decrease in craving.

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