Rewards Rapidly Shape the Brain's Behavior: How Rewards are Linked to Dopamine Release

Monday - January 1 2024, 22:14 UTC - 1 year ago

A recent publication by a joint team of scientists reveals a new process linking specific actions with dopamine release. It showed that mice changed their behavior quickly and dynamically in response to dopamine release, and could even quickly learn a series of actions and distinguish between two elements.

Rewards don’t just reinforce a specific action—they quickly change the whole pattern of how we behave.

Imagine you’re teaching a dog to play fetch. You throw a ball, and your dog sprints after it, picks it up, and runs back. You then reward your panting pup with a treat. But now comes the real trick for your dog: figuring out which part of that sequence earned the treat. Scientists call this the ‘credit assignment problem’ in the brain. It’s a fundamental question about understanding which actions are responsible for the positive outcomes we experience.

Dopamine, a key chemical messenger in the brain, is known to play a crucial role in this process. But exactly how the brain links specific actions to dopamine’s release has remained unclear.

A study published on December 13 in Nature by scientists at the Allen Institute, Columbia University’s Zuckerman Mind Brain Behavior Institute, the Champalimaud Centre for the Unknown, and Seattle Children’s Research Institute sheds new light on this mystery. It reveals how dopamine not only signals a reward but also guides animals to home in on the specific behaviors that lead to these rewards through trial and error.

Intriguingly, the research also shows that the brain’s reward system can swiftly and dynamically alter the full range of an animal’s movements and behaviors. This highlights a sophisticated learning strategy where behaviors are not just reinforced, but actively shaped and fine-tuned through experience, said Rui Costa, D.V.M, Ph.D., the study’s senior author.

“When you reinforce behavior, we often think it’s just that action,” said Costa, the president and CEO of the Allen Institute. “But no: you’re changing the entire behavioral structure. And what was really surprising was how rapid it was.” .

To uncover those insights, the team collaborated with engineers and neuroscientists at the Champalimaud Centre for the Unknown to develop a novel “closed loop” system that could link specific actions by mice to real-time dopamine release. The researchers outfitted mice with wireless sensors to track their movements within a simple controlled space. They then fed this data into a machine learning algorithm, which categorized these actions into distinct groups. The researchers then used optogenetics, a method for controlling neurons with light, to stimulate dopamine neurons once the mice performed predefined “target actions.” .

They found that mice swiftly changed their behavior in response to dopamine release. Initially, they not only increased the frequency of the target action, but also of similar actions and those that occurred a few seconds before the dopamine release. Meanwhile, actions dissimilar to the target rapidly decreased. Over time, this refinement became more precise, with the mice increasingly focusing on the exact action that led to dopamine release.

The study also examined how mice learn a series of actions, unveiling a key process similar to rewinding time to understand what leads to a reward. When actions triggering dopsmine release included two elements—press the lever and run to the corner, for example—the mice learned to divide the process into two distinct steps. This suggests the brain remembers the previous steps enabled by dopamine release and unwinds the sequence sometime later.