According to Eysenck, extraverts have a reticular activating system that is tight, and introverts have an open reticular activating system.
Explanation:
Hans Jurgen Eysenck, a German-born British psychologist, is well-known for his developments in the field of personality and intelligence within the domain of psychology.
As a part of his biological trait theory, he spoke about extraversion and introversion - the former referring to individuals who are extremely expressive and outgoing, while the latter referring to those who are relatively more shy, quiet or reserved in nature.
According to him, the reticular activating system is responsible for controlling the quantities of sensory inputs in the brain. In introverts, this system is wide open (hence introverts tend to avoid any extra stimulation). However, in extraverts, this system can be seen to be somewhat tighter, making them insensitive (and hence craving extra stimulation).
