The extreme way people with BPD experience the world may reflect a glitch in brain dynamics. Typically, the prefrontal cortex, the part of the forebrain responsible for self-control and decision-making, governs the limbic system, an evolutionarily ancient set of brain regions that generate primal emotions such as fear, centered in the amygdala. But people with BPD seem to have less input from the prefrontal cortex to the amygdala. This leads to an overactive amygdala—perceiving threat and rejection where others would not.