Editing Trait theory (section)

===Causality===
Although both major trait models are descriptive, only the three-factor model offers a detailed causal explanation. Eysenck suggests that different personality traits are caused by the properties of the [[brain]], which themselves are the result of [[Genetics|genetic]] factors.<ref>{{cite book|last1=Eysenck|first1=H. J.|last2=Eysenck|first2=M. W.|year=1985|title=Personality and individual differences: A natural science approach|location=New York|publisher=Plenum|name-list-style=vanc}}</ref> In particular, the three-factor model identifies the [[reticular system]] and the [[limbic system]] in the brain as key components that mediate cortical arousal and emotional responses respectively. Eysenck advocates that extraverts have low levels of cortical arousal and introverts have high levels, leading extraverts to seek out more stimulation from socializing and being venturesome.<ref>{{cite book|last=Eysenck|first=H. J.|year=1967|title=The biological basis of personality|location=Springfield, Ill.|publisher=Thomas|name-list-style=vanc}}</ref> Moreover, Eysenck surmised that there would be an optimal level of arousal, after which inhibition would occur and that this would be different for each person.<ref>{{cite journal | last1 = Eysenck | first1 = H. J. | year = 1994 | title = Creativity and personality: Word association, origence, and Psychoticism | journal = Creativity Research Journal | volume = 7 | issue = 2| pages = 209–216 | doi=10.1080/10400419409534525|name-list-style=vanc}}</ref>

In a similar vein, the three-factor approach theorizes that neuroticism is mediated by levels of arousal in the limbic system and that individual differences arise because of variable activation thresholds between people. Therefore, highly neurotic people when presented with minor stressors, will exceed this threshold, whereas people low in neuroticism will not exceed normal activation levels, even when presented with large stressors. By contrast, proponents of the five-factor approach assume a role of [[genetics]]<ref name="Costa1992"/> and environment<ref name="Jeronimus2014"/> but offer no explicit causal explanation.

Given this emphasis on [[biology]] in the three-factor approach, it would be expected that the third trait, psychoticism, would have a similar explanation. However, the causal properties of this state are not well defined. Eysenck has suggested that psychoticism is related to [[testosterone]] levels and is an inverse function of the [[Serotonin|serotonergic system]],<ref>{{cite journal | last1 = Eysenck | first1 = H. J. | year = 1992 | title = The definition and measurement of psychoticism | journal = Personality and Individual Differences | volume = 13 | issue = 7| pages = 757–785 | doi=10.1016/0191-8869(92)90050-y|name-list-style=vanc}}</ref> but he later revised this, linking it instead to the [[dopaminergic system]].<ref>{{cite journal | last1 = Eysenck | first1 = H. J. | year = 1997 | title = Personality and experimental psychology: The unification of psychology and the possibility of a paradigm | journal = Journal of Personality and Social Psychology | volume = 73 | issue = 6| pages = 1224–1237 | doi=10.1037/0022-3514.73.6.1224|name-list-style=vanc}}</ref>