The mythology of the Wild West suggests the person who draws first in a gunfight is usually the first to get shot, and new findings now hint at a reason why this might happen.

Inspired by Hollywood cowboy movies, Nobel Laureate atomic physicist Niels Bohr once conjectured why, during a duel, the gunslinger who drew first was the one to get shot — the intentional act of drawing and shooting is slower to carry out than the "quick draw" response to another gun. Anecdotal reports note that Bohr tested his idea using toy pistols, with the reactive Bohr apparently winning every duel against his colleague George Gamow.

Now an international team of scientists has found a basis for this idea — people move faster when reacting than when initiating the same movement. But the ultimate outcome is not so simple.

Shootout at the O.K. Lab

In laboratory versions of gunfights, the researchers had volunteers each press a row of three buttons. When they faced off against other "gunslingers" — either people directly across from them, people in another room, or computers — the volunteers on average were roughly 10 percent faster when they reacted than when they initiated "shootouts," a boost in speed of roughly 21 milliseconds they dubbed "the reactive advantage."

Still, while participants moved faster when reacting than initiating, reactors only rarely beat initiators. The extra milliseconds it took volunteers to respond to the movements of their opponents greatly offset any benefit the reactive advantage granted.

"As a general strategy for survival, having this system in our brains that gives us quick-and-dirty responses to the environment seems pretty useful," said researcher Andrew Welchman, an experimental psychologist at University of Birmingham in Britain. "Twenty-one milliseconds may seem like a tiny difference, and it probably wouldn't save you in a Wild West duel because your brain takes around 200 milliseconds to respond to what your opponent is doing, but it could mean the difference between life and death when you are trying to avoid an oncoming bus!"

These findings also suggest that Bohr's victories in his duels could not be ascribed to the reactive advantage. Instead, "he was probably just a very good shot," Welchman said.

What's going on?

The researchers now want to learn what is responsible for this difference between intentional and reactive actions. They suggest the brain circuits that control reactive actions could be faster than ones in charge of intentional motions, providing a potentially useful means of promoting survival.

"One idea is that when we are reacting to the things around us in the world, that information comes in from the eyes, gets sent to the back of the brain, and then from the back of the brain up towards the areas that control our movements," Welchman explained. In contrast, when one makes an intentional action, the information goes from the decision areas in the front of the brain back toward the motor areas in charge of movement.

"The key idea is that effectively, the brakes get taken off faster when we are making reactive movements so we can get moving faster than when we're making intentional movements," he said. "That could be responsible for us being 20 milliseconds quicker when we respond to our opponents." However, what one gains in speed might be lost in accuracy, the researchers added.

There might be some evidence for two different brain systems in people with Parkinson's disease — for instance, they might find it far harder to pick up a ball from a table than they would to catch the same ball if it were thrown at them. If Parkinson's does indeed affect areas of the brain that contribute more to intentional actions than reactive ones, it might be possible to develop strategies to ease movement in such patients, the researchers added.

The findings will be detailed online Feb. 3 in the Proceedings of the Royal Society B: Biological Sciences.