This 2014 human study was notable for defining away the limbic system and lower brain from consideration in processing positive and negative stimuli for value.

However, the researchers didn’t fully reveal their biases until the last paragraph of the supplementary material, where they were obligated to comment on a previous study that included the limbic system. Good for the reviewer if that was how the researchers became obligated to deal with the previous study.

It isn’t difficult to include the limbic system in studies of value. For example, the Teenagers value rewards more and are more sensitive to punishments than are adults study found:

• Cerebral areas increased activity when the expected value of the reward increased.
• Limbic system areas increased activity when the expected value of the reward decreased.

http://www.pnas.org/content/111/13/5000.full “Disentangling neural representations of value and salience in the human brain”