1. A stimulus triggers the senses. The brain receives the stimulus instantaneously. It can be something your character hears, intuits, sees, smells, tastes, or touches.
2. The body has an involuntary response that takes a nanosecond. The limbic system evaluates the stimulus and sends chemicals racing through the body as neurons fire, depending on its evaluation of whether the stimulus is negative, positive, or neutral. The brain decides if there is a potential threat or reward.
3. The response triggers a reflexive action.
4. The brain then regains control over the body and makes a conscious decision about how to proceed.
A posited theory is that everyone we meet (and everything we come across) leaves a neural imprint. The brain decides if a person, place, or thing is a friend or foe and whether the next encounter will be negative or positive. The composite images are stored in an easily accessed file folder for comparison. How much a person or thing resembles the positive or negative composites determines how likely you are to like or dislike a new person, place, or thing when you encounter it. It decides whether snakes are lovely or lethal, whether a physical action is comforting or threatening, and whether an action you take is likely to result in reward or punishment.
It compares faces and decides that your new boss looks a lot like the girl you liked in elementary school. Your initial reaction is positive. She may turn out to be perfectly awful.
The brain makes these split-second decisions every second of every day. It is important to understand this process as you write, but it's only necessary to zero in on this part of the response at the most critical turning points of your story.
Next, the body reacts involuntarily to the stimulus. It recoils or reaches out. It startles or is soothed. A character gasps, coughs, sneezes, laughs, or screams. This reaction is embedded deep within the animal part of the brain. It is governed by sheer instinct and raw emotion. It is the fight or flight response at play. His pulse, breathing, and muscles react. His skin erupts in chills. His mouth goes dry. The character is not speaking or moving yet. He flinches, blinks, tenses, and displays a micro-expression.
What happens next depends on how the brain filters the stimulus through the character's conditioning, personality, and emotional connection to the stimulus. It tests the emotion of the moment. The brain decides to override or reinforce the initial involuntary response. If the stimulus is a threat from a comforting person, it causes dissonance. The same is true if the loving gesture is issued from a threatening stimulus. Dick's impulse may be to hug someone. It is awkward when that someone pulls away from it.
Finally, the character's conscious mind takes over and is free to decide which course of action to take next. The body recovers from the initial reflex. It overcomes the muscle memory and moves with intention. Conscious control over his breathing, pulse, and muscles is restored. Dick moves deliberately forward or backward and speaks. He alters his breathing, flexes his trembling knees, or relaxes his tightened gut and jaw. He smiles and shakes hands or fake smiles and avoids shaking hands.
If Dick has been startled, shocked, or wounded, his body recovers. Writers often forget to mention this step of the process. His system returns to normal once the threat has passed. Make sure you show the recovery after a major impact.
Not every encounter needs to reveal every beat. Use more beats when the tension is high, less when the tension is low. Use extreme actions and reactions sparingly. The verbal camera should zoom in on the mechanics during critical parts and zoom out for the noncritical parts.
Next time we will discuss distance and touching. How close is too close?