According to Gray,there are differences among people in the introversion- extroversion and emotional stability. They come from two associated brain systems. 1) The BAS or Behavioural approach system and 2) The BIS or the Behavioural Inhibition System. BAS is composed of areas that affect individuals sensitivity to rewards and their drive to recieve rewards. BAS is responsibale for how impulsive a person is. It has been called the "go" system. BIS is composed of regions involved with sensitivity toward punishment and the motivation to avoid being punished. Can be refered to as "stop" system.

Introverts are opposite. They can be insensitive to rewards but are highly affected by punishment. Where as emotionally unstable people are affected more by rewards and punishment than those who are emotionally stable.
Gray's theory is now more accepted than
Eysenck's theory mainly because it has more evidence behind it and it is more consistent with neuroscientists' knowledge of the brain, neurotransmitters and the function of them. (Bernstein et al, 2008).

According to an article written by Anderson and Berdahl (2002) which introduces the approach/ inhibition theory of power, it is proposed that power tips the balance of activation between the behavioural approach and the inhibition systems.
The behavioural approach system is supposed to regulate behaviour associated with rewards such as food, sex, safety, achievement and social attachment. The presence of attainable rewards and opportunities activates approach- related process that helps the individual pursue and obtain these goals related to the rewards they are seeking.
The article gives an example of positive affect motivates approach- related behaviour scanning for certain rewards (Anderson & Berdahl, 2002, p.1363).

Leading a high power life
(leaders, members of majority groups, people in high socioeconomic status) will activate the approach system for two reasons:
1) Higher power is in conjunction with increased access to rewards, for example financial resources, physical comforts, as well social resources that boost self-esteem, praise and positive attention and
2) When people have power they are aware they will receive less interference from others when approaching potential rewards (Anderson & Berdahl, 2002).

According to Anderson and Berdahl (2002) for complementary reasons, having low power is associated with activating the inhibition system.
When people have low power (followers, members of minority groups, people in low socioeconomic status) they are more subject to social and material threats and they are aware of the threats and constraints put on them by others (Anderson & Berdahl, 2002, p.1364).