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A lot happens in your brain during a simple decision. Here's the tl;dr version.

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If you think your typical day is hectic, imagine how your brain feels. As it turns out, even the simplest decisions require a complex network of brain activity. Somehow, though, even with all that possibility for things to go very wrong, our brains tend to act rationally when faced with decisions.

It all (sort of) started with decoding German messages during WWII. Born in 1912, Alan Turing was, among other things, a math genius way ahead of his time. He invented a mathematical tool that could judge the reliability of information. That tool helped to decipher encoded messages during World War II.

But now, that same tool has a more modern use: According to the Smithsonian, neuroscientists are using it to decode the ways in which our brains make decisions.

The German Enigma machine of the early 1900s created code by swapping the original letters in a message for new ones, producing a piece of (seemingly) indecipherable nonsense. The device also had rotating disks inside that changed the encoding with each keystroke — not easy stuff. But Turing’s tool used an algorithm that simplified the decoding process by helping codebreakers decide whether two messages were useful while looking at the fewest possible number of letters.

That’s also kind of how our brains make decisions. We know this largely thanks to Columbia University neuroscientist Michael Shadlen (who studies rhesus monkeys looking at dots).

We take in information from various sources we experience, like our senses or our memories. As Shadlen writes, “We assign more or less weight to cues that differ in their reliability, calculate expected costs and benefits associated with anticipated outcomes, process elapsed time to meet a deadline or to assess temporal cost, and implement rules (such as deciding on what to decide upon) and policies (balancing accuracy against speed).”

Our brains consistently make decisions using the same processes. At least that’s true of smaller day-to-day decisions. For those bigger existential choices, we have a lot more to figure out.

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