I'm working through the Psychological, Social, and Biological Foundations of Behavior section bank, and am on passage 7, question #56.

The question asks, "Similar activation levels in which brain region were LEAST likely in S and TSD participants when they were viewing the images presented in the study?"

The passage states, "This observation suggests that an increased sensitivity of the reward system to food in sleep-deprived individuals may contribute to obesity."
TSD = total sleep deprivation group and S = sleep group.

The answer is apparently "cerebellum" because "the cerebellum is not a primary structure of the reward system."

However, I thought the question was asking which brain region was LEAST likely to show SIMILARITY between the two groups? Least likely to be similar would mean most likely to be different, right? So cerebellum doesn't make sense, and neither does their explanation. Shouldn't the cerebellum be most likely to show similarity in activation between the groups, not least likely? Is this a mistake, or am I missing something?

I chose A)Nucleus accumbens, because I recall that this is the stereotypical "reward center" of the brain, and it should thus have different activation levels between the two groups.