Ready…Set…Go!


Want to improve your reaction speed? Take a few seconds to focus on the movement you’re about to make, says a new study.

"I shall allow you the use of your premotor cortex, Mr. Bond."

Before a planned movement is converted into actual motion, the brain assembles a “motor plan,” which helps prep the necessary neurons to send signals to muscles extra quickly. The more the brain’s motor plan is optimized for that particular movement, the faster the reaction time will be. Sprinters and wild-west gunfighters should take notes.

This breakthrough comes as a result of some new technologies, which allow researchers to simultaneously monitor the activity of hundreds of neurons. By mathematically analyzing the results of these measurements, scientists are finally starting to understand how the activity of a group of neurons gives rise to muscular movement.

Though the study is published in the journal Neuron, the team leaders were actually electrical engineers – Krishna Shenoy and Maneesh Sahani, who led the study at the Stanford School of Engineering. To measure the neural activity the leads to movement, the team implanted tiny chips with 100 electrodes onto the brains of rhesus monkeys. The electrodes targeted the dorsal premotor cortex (PMd), an area that becomes very active when animals are planning an arm movement.

The scientists trained the monkeys to quickly touch a target whenever it appeared on a screen, and then set about logging their reaction times while measuring their premotor activity.

What the scientists found upsets years of theory about motor planning:

The existing hypothesis, known as “rise-to-threshold,” held that in anticipation of a “go” cue, our brains begin to plan the motions necessary to satisfactorily complete the movement by simply increasing the activity of neurons. Neurons begin to fire, but not enough to cause the movement to take place. Upon the “go” signal, the brain accelerates this neural firing until it crosses a “threshold” initiating the motion. According to the theory, the longer a preparatory period one has, the greater the neural activity will be and, thus, the faster the reaction time.

In other words, the leading hypothesis was that neural activity “builds up,” and then is “released” by a “go” signal. But as the Stanford team found, the switch from planning to motion has much more to do with neural activity focusing in on a specific area, then shooting off down a trajectory when the “go” signal fires:

In graphs of neural activity prior to display of the target, the monkeys’ neural activity appears somewhat scattered. The moment a target is displayed, however, the neural activity concentrates in an activity region that the researchers dubbed the “optimal sub-space.”

Because some points in the optimal sub-space are closer to the intended movement pathway than others are, activity focused in these points leads to faster reaction times. In fact, the researchers got pretty good at predicting what a monkey’s reaction time would be, just by watching the activity in its brain’s optimal sub-space.

The next steps, Shenoy says, will probably involve neural prostheses for people with amputations or paralyses. The better we understand how the brain plans motion, the more we can speed up the response times of robotic limbs and thought-controlled cursors.

But for those of us who just want to win at the “slaps” game, these discoveries hint at the potential for exciting new powers. Which, I promise, I will only use for good.

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