This is what happens when our minds are faced with a split-second decision

If possible, it’s always advisable to take one’s time with decisions, both big and small. Of course, not all situations afford us that luxury.

We’re all faced with split-second decisions in life, such as whether or not to cross a street before the traffic light changes or take on that high-priority client that your manager just offered you. Somehow, though, our minds always seem to make a decision in a pinch.

Up until now, modern science has struggled to understand how the mind can perform such a feat in literal milliseconds. However, a fascinating new study from the University of Colorado Anschutz Medical Campus has uncovered the neurological processes, brain areas, and neurons responsible for the human mind’s ability to make decisions instantly.

“We wanted to know how this kind of decision making takes place,” says senior study author Diego Restrepo, Ph.D., professor of cell and developmental biology at the University of Colorado School of Medicine, in a release. “How, for example, do you decide to swing or not swing at a fastball in baseball?”

The research team found that an understudied portion of the cerebellum looks to be the main facilitator of split-second decisions. This is especially interesting because the cerebellum is usually associated with bodily movements, not decisions.

As more researchers turn their attention to the entire cerebellum, it’s becoming more and more clear that it’s responsible for far more than just motion. Recent research has connected it to cognition, emotion, and even autism spectrum disorders.

More specifically, molecular layer interneurons (MLIs) within the cerebellum were focused on. Using a multiphoton microscope researchers were able to observe the brains of a group of lab rodents in real-time as the animals decided whether or not to drink a water solution. 

Throughout the experiment, researchers periodically released a pleasant odor into the rodents’ environment. In the presence of that smell, the rodents were rewarded with a sugar treat each time they drank some water. But, when the smell was replaced by unscented mineral oil, the rodents would be punished (given a time out) for drinking water.

Initially, the rodents’ MLI responses didn’t seem to change according to smell. However, after some time had passed and the rodents started to learn the smell conditioning, the pleasant reward-associated odor incited a significant jump in MLI calcium responses. Conversely, the mineral oil resulted in a reduction in MLI activity.

Then the study’s authors used a group of chemogenetic agents to subdue and stop all MRI activity in the rodents’ cerebellums. When this happened, all the mice became much more indecisive about when to drink water.

Essentially, these findings confirm that MLIs are involved in both learning and decision-making when it comes to personal benefits and drawbacks.

“Our data indicate that the MLIs have a role in learning valence,” Restrepo notes. “That is, it helps determine whether something is good for me or not.”

So, it appears that MLIs keep track of what helps or hurts an individual, and then reactivates that information instantly when faced with a quick decision.

“We found an entire subset of brain cells that change after learning,” Restrepo concludes. “It sheds further light on how the cerebellum functions and the complex web of connections that go into quick decision making.”

The full study can be found here, published in Nature Communications.