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Brain cells communicate to support decision-making

Every decision, big or small, good or bad, starts somewhere in the brain. But how does it reach that final conclusion?

Deep within the brain lies a decision-making powerhouse: the posterior parietal cortex (PPC). It’s not just a control center, but a network of neurons. Harvard researchers have unlocked some of the secrets of how these neurons work together, giving us a better understanding of how we make decisions. 

“How the brain is organized to help make decisions is a big, fundamental question, and the neural circuitry – how neurons are connected to one another – in brain areas that are important for decision-making isn’t well understood,” said 

Study co-author Wei-Chung Allen Lee is an associate professor of Neurobiology in the Blavatnik Institute at Harvard Medical School. 

Observation in a maze

The researchers studied decision-making processes in the brains of mice by observing their behavior in a maze. Trained to turn left or right depending on visual cues, the mice provided behavioral data on how they make decisions. 

To peek inside the brains (specifically PPC) of these decision-makers, the researchers used a technique called 2-photon calcium imaging. This allowed them to observe activity patterns of individual neurons in the PPC, essentially witnessing how different brain cells “voted” during each choice.

Next, the team analyzed how the neurons were “wired” together, uncovering excitatory connections that boost activity and inhibitory connections that dampen it. 

Decision-making inside the mice brain

The researchers found that when a mouse explores a maze, it chooses a direction beforehand, like turning left. This activates groups of nerve cells in its brain that process that decision. The active groups become stronger, making the chosen path seem more attractive the next time.

Other nerve cells, groups that favored a different option like turning right, were silenced. This helps the mouse stick to its chosen path. 

“As the animal is expressing one choice, the wiring of the neuronal circuit may help stabilize that choice by suppressing other choices,” said Dr. Lee. “This could be a mechanism that helps an animal maintain a decision and prevents ‘changes of mind’.”

How the brain makes clear decisions

The study suggests a clear pattern in the PPC. When you decide something, like what to eat for dinner, two teams of brain cells battle it out. These are “excitatory” and “inhibitory” neurons.

When you start leaning towards one option, say pasta, the PPC sends out signals to reinforce that choice. The signals are amplified by excitatory neurons. They excite and activate other neurons, making your chosen meal seem more appealing and solidifying your decision in your mind.

But the PPC doesn’t just boost your preferred choice. It also actively suppresses signals related to options that are not “pasta.” This suppression comes from inhibitory neurons. They slow down or even stop other neurons from sending messages related to the alternative meal, preventing confusion and helping maintain balance in the decision-making process. This ensures that only one meal wins out, ultimately leading to a clear and focused decision.

The decision-making process

Several factors influence which neurons get activated during decision-making:

What you sense: Your eyes, ears, skin, and nose send information about your surroundings and yourself to your brain. This information, like seeing paths in a maze, triggers specific neurons related to navigation and choosing.

What you’ve learned: Past experiences and memories shape how your brain reacts to situations. Neurons involved in remembering and connecting things might activate based on what you’ve learned in similar situations before.

What you need to do: What you’re trying to achieve influences which neurons get involved. Neurons related to planning, taking action, and getting rewards might light up depending on your goal and the likely outcomes of your choices.

How you’re feeling: Interestingly, hunger, thirst, tiredness, or excitement can all affect your brain activity and decisions. Neurons that manage these internal states might activate to guide your choices towards fulfilling your needs.

How neurons talk: Brain cells don’t work alone. They send signals to each other, exciting or calming each other down. This creates groups of active neurons representing different parts of the decision-making process.

So, when you’re making a choice, your brain has a lot to consider. This complex interplay determines which neurons activate and ultimately guides your decision.

Broader implications

The study shows brain cells in mice activate in a specific order, and those representing “wrong” choices get suppressed as the decision becomes clear. Understanding this process in mice helps us understand how decisions “solidify” in humans.

By learning how animals make decisions, we can learn more about disorders like Alzheimer’s, schizophrenia, and addiction, where people struggle to make good choices. This knowledge might lead to better treatments for these conditions.

The study is published in the journal Nature.

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