Brain scans can hear our thoughts, make us learn by osmosis and even predict our actions. Now a new study claims that functional MRI scans can reliably judge a person’s most basic appetites, predicting future sexual behavior or weight gain.

Scientists at Dartmouth College recruited 58 incoming freshmen women for brain scans, and weighed them beforehand, telling them it was standard procedure. While in the scanner, the women saw various images of food, landscapes, animals and people. The scientists monitored activity in a brain region called the nucleus accumbens, the “reward center” of the brain. Then the women were invited back six months later to take a survey accounting for their behavior afterward.

The women whose brains lit up at the sight of food gained more weight than their counterparts, the authors found. And women whose brains responded to sexy imagery were more likely to be sexually active. “Just as cue reactivity to food images was investigated as potential predictors of weight gain, cue reactivity to sexual images was used to predict sexual desire,” the authors write.

Other studies have used fMRI to predict behavior — one of them found the scans can more accurately predict a person’s behavior than the person can. In that study, the scans were examining the medial prefrontal cortex and the precuneus, which are related to self-awareness. This new study examines our innate animal instincts, and it, too, can apparently be pretty accurate.

The Dartmouth team’s goal is to understand the physiological basis for willpower, and how environmental triggers can undermine it. If your brain activity spikes when you see a picture of a cake, you might be more likely to order a slice in a restaurant if the server brings over the dessert tray, for instance. Understanding the neural basis for this behavior could lead to treatments or at least awareness that could help people better control themselves.

“You need to actively be thinking about the behavior you want to control in order to regulate it,” explains William Kelley, associate professor of psychological and brain science and a senior author on the paper. “Self-regulation requires a lot of conscious effort.”

The paper appears in the Journal of Neuroscience.

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