What's the science?
Serotonin is a neurochemical in the brain important for feelings of happiness. A current theory of serotonin function suggests that serotonin is involved in patience and inhibiting actions. Currently, we do not understand whether this involves patience in the sense of behavioral inhibition (i.e. not acting) or patience in the form continuing to act (i.e. persistence).This week in Nature Communications, Lottem and colleagues show that serotonin release in the brain is responsible for persistent behavior in mice.
How did they do it?
They used optogenetics to activate serotonin neurons (in the dorsal raphe nucleus) in the brains of mice during a foraging experiment. During foraging, animals explore an area for food or water, and at some point, they must give up and move on to a different area. This means the animal requires active patience (persistence) when exhausting their search in a given area. Water-restricted mice were required to “nose poke” to obtain a water reward while foraging an area. The probability of obtaining water at each reward station was reduced with each nose poke. The authors used a higher number of nose pokes as a measure of persistence, while a reduced number of nose pokes meant inhibition of behavior. They also used video tracking to measure how long it took for mice to switch to another area.
What did they find?
Mice exhibited optimal foraging behavior, meaning they optimized the trade-off between time spent searching an area for water and leaving to find reward in another area. The mice that received serotonin neuron stimulation performed a greater number of nose pokes compared to mice who did not receive stimulation. They also took longer to leave an area (but not to move in general) suggesting they were more persistent. The authors modelled this leaving behavior using a proportional hazards model to show that serotonin neuron stimulation reduced the probability of a mouse leaving an area.
What's the impact?
This is the first study to show that serotonin neuron firing is responsible for active persistent behavior. Previously, it was hypothesized that serotonin was involved in patience through inhibiting behavior. We now know that serotonin neuron firing is involved in persistence. This extends what we know about the role of serotonin in behavior.
Reach out to study author Dr. Zachary F. Mainen on Twitter @zmainen and @mainenlab
E. Lottem et al., Activation of serotonin neurons promotes active persistence in a probabilistic foraging task. Nature Communications (2018). Access the original scientific publication here.