July 17, 2024

Why Did You Move Your Hand Just Now? Linking Free Will and Movement

Author: Kate Findley
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By Peter M. Vishton, Ph.D.William & Mary
Edited by Kate Findley, The Great Courses Daily

We like to believe that we’re in control of all our decisions. But as Dr. Peter M. Vishton explains, many of the actions we take are not governed by free will alone—including something as simple as lifting our hand!

Close up of a man's hand
Activity increases in the brain’s left or right motor cortex just before muscle movement begins in the body and before a person is aware of a decision to move. Photo by Liderina / Shutterstock

Free Will and Movement: The Surprising Connection

When it comes to the connection between free will and movement, you would think that your physical actions are always preceded by a conscious decision. But did you know that we can tell how people are going to move before they do so?

Indeed, it’s possible to know how they’re going to move even a few hundred milliseconds in advance. If you think about moving your left hand, even if you don’t actually move it, your right motor cortex activates a bit.

Studies using functional magnetic resonance imaging (fMRI) have suggested that, for some decisions, the lag time can be several seconds. In this type of study, you lay in the fMRI scanner and look at pictures of faces, pondering whether each face looks trustworthy or not. 

As you’re pondering, activity begins increasing in either your left or right motor cortex, the one that will cause the right or left hand to press the button. At some point, this activity becomes great enough that it causes a movement of your hand.

But well before your hand moves—in fact, several seconds before you’re even aware that you’ve made the decision—the person running the fMRI scanner can accurately predict the choice that you’ll make. 

Inducing Movement through Transcranial Magnetic Stimulation

Some recent studies by neuroscientist Alvaro Pascual-Leone have taken this investigation into movement and free will much further. He used a technique called transcranial magnetic stimulation (TMS). 

TMS sends a jolt of electromagnetic energy through the skull to the cortex and causes a burst of activity. If that burst is sent to the correct spot in the motor cortex, for instance, it’s possible to make your arm twitch. 

“If I stimulate a spot in the right motor cortex, the left hand twitches,” Dr. Vishton said. “For a corresponding jolt in the left motor cortex, the right hand will twitch. Our sensory and motor systems all have this crossover or contralateral organization.”

Pascual-Leone asked his participants to watch a screen, and when they received a cue, to decide whether they would twitch their left or right hand. They weren’t supposed to move right away, just decide how they would move a few seconds later. 

After a delay of a few seconds, a second cue was delivered, at which point the participant made the movement they had decided to make.

For many of the trials, Pascual-Leone didn’t do anything but record these activations. Participants would get the first cue, and they would decide to move one hand or the other. Then the second cue would occur, and the participant would move.

In some trials of this experiment, Pascual-Leone would deliver a TMS jolt to the motor cortex that the participant had chosen to move. The participant would move but rarely notice that they had.

The experimenters were causing the hand movement by stimulating the motor cortex, but the participants were about to do that same thing themselves anyway.

Who’s Actually in Control Here?

For a few key trials in this experiment, however, when the signal to move was given, Pascual-Leone would deliver a jolt to the motor cortex that the participant had not selected. This caused the wrong hand to move. 

Now, if our conscious experience of decisions is in control, this should feel strange—really strange. You’ve decided to do one thing, but your body has been hijacked and made to do something else. 

The strangest thing about the results of this study is that the participants didn’t even seem to notice that their brains had been hijacked.

Most participants had a very simple description of the experience. When asked why they moved their left hand, when their brain activity made it seem like they were going to move their right hand, most participants gave a nonchalant answer: “I just changed my mind.”

In this experimental situation, it’s clear that the experimenter—not the participant’s free will—is in control of the movement. The surprising result here is that participants don’t feel strange when they don’t have conscious control of their own movements. 

These experimenters argue that this is because we aren’t typically in control of those movements, even when we aren’t hooked up to a TMS stimulator in this type of experiment. The results of these studies by Pascual-Leone and others suggest that it doesn’t feel unusual—indeed, that it isn’t unusual—for our conscious mind to not be in control of our actions.

Think about this the next time you reach for a bag of chips or a pint of ice cream. 

This article was edited by Kate Findley, Writer for The Great Courses Daily.
Image of Professor Peter Vishton

Dr. Peter M. Vishton is Associate Professor of Psychology at William & Mary. He earned his Ph.D. in Psychology and Cognitive Science from Cornell University. Before joining the faculty of William & Mary, he taught at Northwestern University and served as the program director for developmental and learning sciences at the National Science Foundation.

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