Sleepless nights have a direct impact on areas of the brain that regulate decision making processes, making us crave French fries as opposed to Greek yogurt and strawberries. “What we have discovered is that high-level brain regions required for complex judgments and decisions become blunted by a lack of sleep, while more primal brain structures that control motivation and desire are amplified,” says Matthew Walker, a UC Berkeley professor of psychology and neuroscience and senior author of the study.