The results, according to University of California San Diego researchers Green and Murphy, were pronounced: “[Diet soda drinkers] who consumed a greater number of diet sodas had reduced caudate head activation. These findings may provide some insight into the link between diet soda consumption and obesity.”
Researchers posit that consumption of diet soda had confused the reward loops normally processed by the caudate head: because sweetness was no longer a reliable indicator of incoming calories, the brain had trained itself to respond less in the face of sweet flavors. Unreliable sweet tastes threw off normal predictions about calories and energy in the changed brains of diet soda drinkers—making it more likely that these people would consume additional calories later in the day.
We can’t always foresee the unintended negative responses our brain makes—who would have thought diet coke might do quite the opposite of what its name suggests?—but there are positive ways to harness your brain’s ability to change. Just a little Lumosity training every day, for example, can change your brain for the better: instead of confused reward signals, you could experience faster processing speed, quicker flexibility, and improved problem solving.