Dartmouth researchers studying rats have recently discovered that activating designer neural receptors can suppress cravings in a brain region that’s involved in triggering those same cravings. This study is the first to systematically show how designer brain receptors and designer drugs work together to change how cues for food stimulate motivation. These findings, which could help scientists fight unhealthy habitual behavior in humans.
Humans are bombarded in our everyday life with cues that garner our attention and trigger us into buying products, or rewards. For example, the golden arches of McDonald’s can produce cravings for fast food even if you aren’t hungry. Scientists study this phenomenon with sign-tracking, also known as autoshaping, which is an experimental conditioning in which the reward is given regardless of how the subject behaves. For their study, the researchers were mostly interested in whether or not the ventral pallidum, a brain region implicated in processing reward, is also involved in sign-tracking. It’s previously been impossible to repeatedly activate brain areas like this one and temporarily study how cues become valuable in themselves. Yet thanks to a new technology called DREADDs, that’s all changed. DREADDs are engineered receptors that are introduced into neurons using viruses, which shut down neurons as a sort of remote control.
The DREADDs technology allowed Dartmouth researchers to inactivate the ventral pallidum repeatedly and temporarily during tests where a lever was inserted into the experimental chamber for 10 seconds, which was then followed by a food pellet reward when the lever was withdrawn. Even if the food was delivered regardless of how the rat behaved, they pressed and bit the lever as if it were the reward itself. These results showed that activating DREADDs in the ventral pallidum before each training session blocked this behavior, and recordings of individual neurons in the ventral pallidum after DREADD activation revealed that ventral pallidum activity can become suppressed or excited to various speeds and amounts.
The results of this test are the first to show that the ventral pallidum is necessary for attributing value to cues that are paired with rewards, which the researchers say is surprising, since the ventral pallidum was historically considered to just be an area for expressing motivations in behavior. If you’d like to learn more about this study, you can click here!