Manipulated mouse brains reveal that brain structure regarded for fear also has role in rewards

As scientists get better at parsing how complex activity like emotions are processed in our brains, it seems that we may have been unfairly painting at least one structure as a bit of a pessimist. The amygdala, two almond-sized structures towards the center of your brain, have been long associated with processing emotion and decision-making. Most famously, this is the part of your brain credited with responding to potential danger with either ‘fight or flight,’ an instant and occasionally misguided way to quickly avoid harm by challenging or escaping adversaries.

To dig deeper into how the amygdala does its job, mice were altered and equipped for optogenetic manipulation. Their brains were injected with a virus that then doped their amygdalas with light-sensitive proteins. This then allowed for light to be used as a trigger for those doped neurons, allowing researchers to control specific brain cells by piping light into the mice’s brains. This process has been used in a variety of experiments, and in this case it allowed researchers to see exactly what kind of stimulus different cells in the amygdala would respond to.

More positive motivations

While some groups of these brain cells did seem tied to fear-oriented stimuli, which for the mice meant bitter tasting water or small electric shocks to the feet, they were in the minority. Most of the tested cells actually responded to positive rewards. Once mice had experienced light exposure, they sought it out again, indicating it being a positive experience.

This doesn’t completely rewrite our model of what the amygdala does, but it may prove helpful on a couple of fronts. Since fear is still a factor in the amygdala’s circuitry, it may hint at new ways to help people cope with traumatic memories or depression. One a more general basis, it may also help explain why slightly scary experiences, like a scary movie, can feel fun instead of just stressful. It seems that there’s a bit of reward tied to our fear feedback, and that like so many things in the brain, there are a lot more questions to be answered.

Source: Scientists identify brain circuit that drives pleasure-inducing behavior by MIT, Science Daily