Free will might have been the province of philosophers until now, but we’ve cracked the problem with an fMRI. Neuroscientists from Johns Hopkins report in the journal Attention, Perception, & Psychophysics that they were able to see both what happens in a human brain the moment a free choice is made, and what happens during the lead-up to that decision — how activity in the brain changes during the deliberation over whether to act.

“How do we peek into people’s brains and find out how we make choices entirely on our own?” asked Susan Courtney, a professor of psychological and brain sciences and coauthor of the report. “What parts of the brain are involved in free choice?”

The team devised a novel way to track a participant’s focus without using cues or commands, avoiding a Schrodinger’s-like dilemma of altering the process of choice by calling attention to it. Participants took positions in MRI scanners, and then were left alone to watch a split screen as rapid streams of colorful numbers and letters scrolled past on both sides. They were asked just to pay attention to one side for a while, then to the other side. When to switch sides, and for how long to look, was entirely up to them. Over the duration of the experiment, the participants glanced back and forth, switching sides dozens of times.

With regards to connectivity in the brain, the actual process of switching attention from one side to the other was tightly linked with activity in the parietal lobe, which is sort of the top back quadrant of the brain. Activity during the period of deliberation before a choice took place in the frontal cortex, which engages in reasoning and plans movement. Deliberation also lit up the basal ganglia, important parts of the deep brain that handle motor control, including the initiation of motion. The basal ganglia has also been an important target for research on dopaminergic diseases like Huntington’s and Parkinson’s, but the area has also been implicated in OCD, which has a lot to do with attention and volition.

Connectivity isn’t the only important factor here, though. Participants’ frontal-lobe activity began earlier than it would have if participants had been cued to shift attention, which demonstrates that the brain was planning a voluntary action rather than merely following an order. Following commands or running through practiced actions, like the way you can sometimes drive home on autopilot, don’t need the same lead time. Timing is crucial.

It’s worth pointing out, too, that this is an entirely novel research tool. It should be examined and held up to criticism and comparison, because it stands to revolutionize how we study not just the brain but the mind. Now that scientists have a way to follow the execution of free will, they can use the technique to watch what’s happening in the brain as people navigate more complex decisions, such as weighing short-term rewards against long-term rewards — and perhaps even pinpoint the tipping point between them.