New research uncovers patterns in the resting brains of highly sensitive people. Sensory processing sensitivity (SPS) is a biological trait present in roughly a third of the population. In a world of constant information overload and stress, it’s a characteristic that can result in a variety of behaviors, from emotional outbursts to withdrawal, overwhelm, and procrastination. “Behaviorally, we observe it as being more careful and cautious when approaching new things,” says Bianca Acevedo, a researcher in the University of California, Santa Barbara’s department of psychological and brain sciences. “You might see this behavior anywhere, from fruit flies to humans.” In a new situation, those with the trait are more likely to hang back and see what happens, she explains.