As we go about our daily lives, we do not simply react to the world around us. Instead we build up mental representations of the world and use these to guide our behavior. For example, we know that if we are hungry we can go into the kitchen to get a slice of our favorite cake. But we also adapt our behavior when circumstances change. If you have just eaten an entire box of cookies you are unlikely to go looking for cake.
Which parts of the brain help us to adapt our decisions to reflect our circumstances? To find out, Baltz et al. trained mice to press levers in order to receive sugar water. In initial experiments the mice completed the training while not hungry. Afterward, some of the mice were placed on a diet that made them hungry. A re-exposure period then occurred where the mice could taste more sugar water without having to press the lever. Finally, the next day, they were given the opportunity to press the levers again.
Mice that were hungry during the re-exposure period pressed the levers more than mice that had been re-exposed while full. Further experiments showed that this was true regardless of how hungry the mice were when they first learned the task. The mice updated how much they valued the sugar water — and so changed how eagerly they tried to obtain it — based on how hungry they were during the re-exposure period.
Baltz et al. repeated the experiments, but this time blocked the activity of a brain region called the orbitofrontal cortex in the mice during the re-exposure period. This prevented the mice from updating how much they valued the sugar, and so they did not adjust their behavior accordingly. If hungry mice had performed the first training stage when they were full, they pressed the levers less often than expected after the re-exposure period. Likewise, full mice who had trained when they were hungry pressed on the lever more times, as if they were still hungry. This suggests that the orbitofrontal cortex helps to update the values that guide decision-making.
There are many disorders that can impair decision-making and prevent people from adjusting their behavior when circumstances change. These include addiction, in which affected individuals also show altered activity in their orbitofrontal cortex. This raises the possibility that in the future we may be able to treat disorders like addiction by restoring normal activity in this region of the brain.
To find out more
Read the eLife research paper on which this eLife digest is based:
