I've just begun to read Brain Rules, in which the John Medina presents peer reviewed and replicated studies delineating how our brains function, what inhibits that function, and what we can do to illicit the best possible outcomes from our brains.
The chapter on stress and its effects on the brain were of particular interest. Therefore I offer below the definition of stress that can sometimes inhibit the functioning of our brains and sometimes give us the power to think more effectively.
Writers who are creating complex characters interacting in situations which increase readers desire to turn the page may find these findings, these definitions, useful.
A measurable physiological response: There must be an aroused physiological response to the stress, and it must be measurable by an outside party. I saw this the first time my then 18-month-old son encountered a carrot on his plate at dinner. He promptly went ballistic: He screamed and cried and peed in his diaper. His aroused physiological state was immediately measurable by his dad, and probably by anyone else within a half mile of our kitchen table
A desire to avoid the situation: The stressor must be perceived as aversive - something that, given the chic, you'd rather not experience. It was obvious where my son stood on the matter. Within seconds, he snatched the carrot off his plate and threw it on the floor. Then he deftly got down off his chair and tried to stomp on the predatory vegetable.
A loss of control: The person must not feel in control of the stressor. Like a volume knob on some emotional radio, the more the loss o control, the more severe the stress is perceived to be. This element of control and its closely related twin, predictability lie at the heart of learned helplessness. My son reacted as strongly as he did in part because he knew I wanted him to eat the carrot and he was used to doing what I told him to do. Control was the issue.
Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School,
Seattle, Washington 2014