Luckily, we usually like what we want and want what we like. Still, in some situations we may like something without wanting it, for example, when we already own bed, we may not want to own another one, even though we like it. Conversely, addiction has been portrayed as a situation where we may want a drug of abuse without really liking it anymore. Together, wanting and liking can be viewed as two often converging but sometimes complementary aspects that determine the value of goods.
Animal researchers made headway with elucidating how the brain processes these two aspects of the value of goods. They measured “liking” with positive facial expressions, (e.g., licking in response to sugar solution) and “wanting” with approach behavior and found that a region in the center of the brain, called the ventral, striatum plays a role for both. However, it remained unclear how the brain makes it possible that in some situations our behavior is driven by liking and in other situations by wanting.
The present study investigated this issue with everyday consumer goods (such as a padlock, a candle, and sunscreen). While we scanned their brains with functional magnetic resonance imaging, participants viewed one good at a time, and for each good, provided judgments of how much they wanted the good and, separately, of how much they liked the good. Thus, we measured wanting and liking in a similar fashion, providing a close match between the two judgment types regarding sensory stimulation and motor output.
We aimed to reduce the normally tight link between liking and wanting by having participants play a game in the middle of the experiment. For this game, participants came out of the scanner. Each participant won half of the goods and put these goods away in a bag to take home at the end of the experiment. Then, they went back into the scanner and provided another set of wanting and liking judgments for each good.
When we compared judgments before the game with those after the game, we found that after the game, participants wanted the goods they had won less than before the game. For example, if they had won a padlock in the game, they subsequently wanted the padlock less but still liked it just as much. Conversely, they liked the goods they had not won less than before the game but still wanted them as much as before the game. It is possible that the disappointment of not having won a particular good reduced how much participants subsequently liked the good, although we did not directly test this possibility.
Next, we asked how the brain processes wanting and liking. To do so, we looked for brain regions where activity increased in sync with the degree to which a participant wanted or liked a good. Participants differed in their evaluations of the goods. We, therefore, took the individual judgments of each participant and correlated them with the participant’s brain activity. Then, we localized brain regions where activity increased with evaluations across all participants. We found regions with such activity in the front and bottom of the brain. Specifically, activity in one region (medial prefrontal cortex) increased with wanting while activity in another region (central orbitofrontal cortex) increased with liking. Importantly, both of these regions encoded wanting or liking levels irrespective of whether participants provided wanting or liking judgments.
So, what did the ventral striatum do? In keeping with the animal literature, activity in the ventral striatum increased with both wanting and liking levels. In contrast to the two regions described above, though, activity increased with wanting levels only during wanting judgments and not during liking judgments. Conversely, during liking judgments, activity increased with liking but not with wanting levels. Thus, the ventral striatum switched between processing the degree of wanting or liking depending on whether participants made wanting or liking judgments. In other words, activity in the ventral striatum reflected one or the other aspect of the value of goods depending on which aspect was behaviorally relevant.
In a final step, we investigated whether and how the ventral striatum communicated with the wanting and liking regions in the front of the brain. We found that during wanting judgments, the more strongly participants wanted the good the more strongly the ventral striatum interacted with the wanting region in the front of the brain. Conversely, during liking judgments, the ventral striatum interacted with the liking region in the front of the brain according to the degree to which participants liked the good.
Our findings inform models of brain organization by elucidating the interplay between the ventral striatum and regions in the front of the brain during value judgments. Moreover, they illustrate how the brain contributes to selecting between different aspects of value. We show that behavioral relevance is particularly important for the ventral striatum while other regions stick to processing one or the other aspect of value irrespective of current behavior. Our findings may provide a knowledge basis for targeted interventions aiming to reduce increased wanting levels (craving) in addiction and obesity.
These findings are described in the article entitled Frontostriatal pathways gate processing of behaviorally relevant reward dimensions, recently published in the journal PLOS Biology.