The same brain region can both motivate us to undertake a learned behavior or suppress it altogether, a new study found. The results will help us better understand how our brain stores memories and how they’re called upon when needed.
While there is a general consensus that different memories are stored in different areas of the brain, there has been a lot of debate if each area can hold contradicting memories — those that control opposing behavior. For example, are the behaviors for a red or green traffic light encoded in the same area of the brain?
Pushing both ways
Questions like this one may seem a bit like nit-picking, but they’re actually really important in understanding us and our minds. Memories make us who we are. They’re also what the brain relies on to decide when and whether to take an action. So scientists are obviously keen on understanding how they work.
A new study from The Scripps Research Institute comes to answer this question. It is the first to offer proof that the same brain region can both motivate and suppress the same learned behavior.
“We behave the way we do in a specific situation because we have learned an association — a memory — tying an environmental cue to a behavior,” said Nobuyoshi Suto, TSRI Assistant Professor of Molecular and Cellular Neuroscience and co-author of the study.
“This study provides causal evidence that one brain region can store different memories.”
Suto’s work focuses on the brain structures that control motivation. For the study, he and the team trained rats to press a lever to get a reward of sugar water. After they got this down (the rats caught on pretty fast) the researchers further trained the animals to recognize two colored lights: green if the reward was available when pressing the lever, red if they would receive none. The rats quickly started adjusting their behavior after training in response to the colors. They pressed the lever more often when the green light was on, and didn’t bother with it when the red one was shining.
Based on previous electrophysiology studies, the team suspected that the mice’s brains stored both sessions of training they received in a region of the brain called the infralimbic cortex.
“We’ve seen correlational evidence, where we see brain activity together with a behavior, and we connect the dots to say it must be this brain activity causing this behavior,” said Suto.
“But such correlational evidence alone cannot establish the causality — proof that the specific brain activity is directly controlling the specific behavior.”
A weapon against addiction
The scientists then started systematically switching off specific groups of brain cells, or ‘neural ensembles’. These ensembles react to ques signaling if the reward is available or not. With the neurons inactivated, the rats didn’t perform any of the behavior encoded in the memories of those ensembles.
This proves that distinct neural ensembles in the same region of the brain directly control reward-seeking behavior or its suppression. Suto called the findings a step towards understanding how different memories are stored in the brain. He says the findings could help battle addiction by discovering which neurons are activated to motivate or prevent drug relapse.
In the future, he’d like to look at what other brain regions these infralimbic cortex neurons may be communicating with. In addition, he also would like to determine the brain chemicals mediating the promotion or suppression of reward seeking.
The full paper “Distinct memory engrams in the infralimbic cortex of rats control opposing environmental actions on a learned behavior” has been published in the journal eLife.
