There are many biological theories for personality, but for this article, we will look at the following psychologists and their theories: Jeffrey Gray’s Reinforcement Sensitivity Theory, and Hans Eysenck's Three-Factor Model of Personality (PEN model).
Reinforcement Sensitivity Theory
Jeffrey Gray’s Reinforcement Sensitivity Theory is based on the notion that we use three types of biologically-driven responses when faced with stress or fear. It posits that everyone has a specific response method when faced with certain stimuli. These individual reactions can underlie personality traits for anxiety and impulsivity.
The three responses that people use when faced with stress or fear are called the fight, flight, or freeze response. This process explains that the person will either fight (face the stimuli head-on), fly (run away from the stimuli), or freeze (not react to stimuli) in stressful or fear-inducing situations. How one instinctively reacts can correspond with personality traits linked to anxiety, overthinking, impulsivity, and worrying.
Mark, Andrew, and Greyson are currently on a hike in the Appalachian mountains. They see signs warning of bear dens nearby. They overlook the signs because it is winter time and they know that it is hibernation season. As they continue to walk, they suddenly hear loud rustling in the bushes nearby. A large bear pops out scaring the three boys. Mark runs away screaming, while Jake is frozen in fear, and Greyson is trying to get his pepper spray out. Based on their reactions, Mark chose flight, Jake chose freeze, and Greyson chose to fight.
In North America, there are around 11 brown bear attacks reported annually, with most surviving the encounter. National parks that have bear residents suggest that the best way to survive an attack is to stay calm and collected. You do not want to run away screaming, as this can cause the bear to attack. If you do encounter one, you should back away slowly with your arms raised. If the bear does charge, lay down in a fetal position and cover your head with your arms. Bear spray does work, but it is not 100 percent effective.
How would you react?
Jeffrey Gray also introduced two behavioral systems that coincided with neurobiological processes.
Gray's Behavioral Inhibition System
Gray theorized that our responses to situations we associate with negativity can be predicted, because our brain recalls previous reactions to the same event or environment. The behavioral inhibition system is a neurobiological system that can predict our response to specific stimuli, because of earlier experiences that we viewed as negative.
Angelica discovered that she was highly allergic to shellfish after trying it for the first time. Now, whenever she sees shellfish, she gets anxious, as she recalls her trip to Urgent Care for treatment.
This behavioral system is associated with personality traits that involve carefulness, trust, anxiety, and emotionality.
Gray's Behavioral Activation System
In contrast, Gray's behavioral activation system suggests that our brain/body is predisposed to pursuing and achieving goals due to our mind's positive association. The behavioral activation system is a neurobiological system that promotes motivation and encourages the pursuit of goals based on experiences that we view as positive.
Sammy creates a goal for each month through the year. This started as a way for her to deal with procrastinating, but over time, it became a habit. She enjoyed the feeling of completing her monthly goal, which motivates her to continue setting goals every month.
Explanations 
Exams 
Magazine 
