A video game has helped scientists find the precise place in the brain where decisions are assembled, half-a-second before a person acts on them, according to a new study. Researchers at the University of California (UC) San Francisco and UC Berkeley logged brain activity just behind a subject’s eyes, known as the orbitofrontal cortex. The patients who took part in the study already had electrodes secured in that part of the brain for surgical evaluations of epilepsy. The research team noticed that side-by-side parts of the brain were signalling in opposite direction. One side leaned towards “do it” and the other towards “don’t do it.” Their study, published in Nature Neuroscience, has the potential to reimagine how conditions like depression, obsessive-compulsive disorder (OCD) and gambling disorders, which display imbalances of risk-taking and caution, are treated. “We’ve long suspected that this region was where the brain weighs reward against risk, but we’ve never been able to measure it while it is happening in the human brain in real time until now,” Dr. Edward Chang, MD, co-senior author of the study, said in a release. In other studies that examined how decisions are weighed, Dr. Clara Starkweather, a neurosurgery chief resident at UC San Francisco, found that participants appeared bored and not compelled to take chances, or receive a reward. “They’d be falling asleep, and I thought there was no way they really cared about what they were doing,” Starkweather said. “But then I’d see patients sitting in their beds playing Candy Crush, getting really into it.” That’s what helped Starkweather design an immersive video game, which got study participants to make their way through a series of hallways lined with a different number of bombs, to try and reach a tower of glowing treasure chests. “There’s just one decision point — whether you go down each hallway,” Starkweather said. The participant’s electrodes examined their brain activity down to the millisecond of when decisions were made. Sides of the brain worked like a tug-of-war Starkweather tracked the recorded activity of six participants across their orbitofrontal cortices. The region known as the medial orbital, near the centre of the eyebrows, spiked in activity right before participants took a risk, like going down one of the bomb-lined hallways. A section approximately two centimetres away, closer to the side of the eyebrows, did the opposite — it would spike before participants avoided a risk by forgoing the bomb-lined hallway. Researchers found that the two parts moved in opposite directions, right to the millisecond. Using a computer model, Starkweather found the two sides acting like a tug-of-war, with one side’s signal spiking as the other dropped, and vice versa, until one side won in the decision-making. “Most models of decision-making assume the brain gradually ramps up evidence until it crosses a threshold, like a dial slowly turning,” said Dr. Robert Knight, professor of Psychology and Neuroscience at UC Berkeley and co-senior author of the study. “What we saw instead was more like a switch flipping back and forth, oscillating between two extremes until one held.” Potential for more targeted treatment Risk and risk avoidance is a major part of many psychiatric issues. By understanding exactly which smaller areas of the brain inspire different behaviours, researchers believe it could lead to more targeted and useful stimulation. “Right now, psychiatry mostly relies on asking people how they feel,” Starkweather said. “I want to give it something more objective: a real, measurable signature of how someone’s brain weighs risk, so treatment can target the specific circuit that’s off, in addition to a mood score.” You can play the online video game here.
