How your brain makes a decision before you know it

Before you make a decision, your brain is already busy. It starts pulling in evidence, thinking through options, and slowly leaning toward a choice – all without you even realizing it.

Take a simple situation: two drivers in rush hour traffic. They both see the same congested road. One hits the gas to merge. The other taps the brakes and waits.

Same scene, different reaction. Why? That’s a question that scientists have been trying to answer for years.

Decision-making in the brain

Researchers from Princeton University, working with teams from Cold Spring Harbor Laboratory, Stanford University, and Boston University, may be closer to cracking the code.

The study was focused on how individual brain cells – each with its own quirks – somehow work together to land on a decision. In particular, the team investigated the dorsal premotor cortex – a part of the brain that helps turn decisions into actions.

When we choose to reach, move, or act, the dorsal premotor cortex is in play. But it’s not as simple as one neuron equals one thought. The activity here is all over the map.

The researchers trained rhesus macaques to look at a checkered screen and figure out whether red or green was more dominant. Sometimes the answer was obvious, while other times it was tough to call.

Signals from individual neurons

While the monkeys made their choices, the scientists recorded signals from individual neurons.

The researchers found that even during the same trial, the neurons didn’t behave in sync. The monkeys showed a wide range of responses, something scientists call “heterogeneity.”

Dr. Tatiana Engel, an associate professor at the Princeton Neuroscience Institute, is the senior author of the study.

“The widespread assumption is that this heterogeneity reflects the complex dynamics involved in cognition,” said Dr. Engel. “But surprisingly, we found that this apparent complexity arises from a very different neural coding principle.”

Neurons work together for a decision

The team developed a new type of computational model to help explain this complexity. It revealed that a neuron’s behavior is shaped by two key factors.

The first is tuning – when a neuron responds and what kind of decision it reacts to. The second is neural dynamics – how the brain’s internal state influences that activity as it unfolds over time.

Imagine a rolling landscape. In this model, valleys represent stable decisions. As neurons activate, their patterns move like a ball rolling down a hill.

On steeper slopes (easier choices), the ball moves quickly toward a clear answer. On flatter ground (harder decisions), the ball wobbles more, making mistakes more likely.

A coordinated journey in the brain

When the team compared this model to real brain data, it held up. The tuning stayed the same no matter how easy or hard the task was, but the shape of the mental terrain shifted.

That shift helped explain why neurons that look random on the surface are actually following the same deeper logic.

“Think of it like a group of skiers descending a mountain,” explained Dr. Engel. “Each prefers a slightly different path, but all are shaped by the same slope beneath them.”

“Similarly, each neuron has its own preference and activity, but the group of cells collectively in the premotor cortex takes a coordinated journey and gradually settles into a stable state that represents the decision.”

Why this matters beyond the lab

The study helps decode how the brain works when we’re weighing choices, especially the tricky ones. That kind of insight is crucial – not just for understanding everyday decision-making, but for understanding mental health disorders.

In conditions like schizophrenia or bipolar disorder, decision-making can be disrupted. Knowing how neurons usually coordinate could help pinpoint what’s going wrong. It also opens the door to designing more targeted therapies that focus on decision-related brain activity.

The team isn’t done yet. Their next step is to dig deeper into the roles of different types of neurons and how their connections shape this internal landscape.

“Every decision is unique,” said Dr. Engel. “But by digging down to the level of single trials and single neurons, we can start to make sense of it.”

The full study was published in the journal Nature.

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