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Neurobiological dimensional models of personality aim to account for the structure of personality traits and disorders through links to neurotransmitter systems. Three such models are reviewed: those of Cloninger, Depue, and Siever. While these proposals have heuristic value, none of them has obtained strong empirical support. Our current understanding of neurobiology is insufficient to develop a model of personality on this basis. At this point, dimensions of personality should be derived from factor analysis rather than from neurobiological theories.
Personality disorders can be understood as reflecting pathological amplifications of personality trait profiles (Siever & Davis, 1991; Livesley et al., 1998; Depue & Lenzenweger, 2001; Costa & Widiger, 2001; Paris, 2003). In fact, all of psychopathology, whether on Axis I or Axis II, need not necessarily fall into categories, and reflects interactions between a few broad dimensions (Krueger, 1999). Many researchers have therefore supported, at least in principle, the development of a dimensional model that can describe both normal traits as well as personality disorders. Another reason for adopting such a model is that research has failed to identify any consistent biological factors that correlate with the current categories of personality disorder on Axis II, whereas many studies have shown relationships between trait dimensions and measures of brain function (Paris, 2003).
However there has been a lack of consensus as to which model should be adopted. There is also some doubt as to whether dimensional models capture the clinical picture of certain well-researched categories, such as borderline personality disorder (Morey and Zanarini, 2000). The situation is well summarized by Matthews, Deary, and Whiteman (2003, p. 295): ". .. research on personality disorders is in a state of crisis. The current categorical schemes lack validity, but there is not yet agreement about whether to move to a dimensional system, or which one might be preferable."
Historically, there have been two approaches to defining personality dimensions. One is primarily empirical, based on the results of factor analysis of self-report data, yielding broad traits that are relatively independent of each other, and which can be further subdivided into narrower facets or subtraits. While a number of such schema have been developed, the most widely researched is the Five-Factor Model (FFM; Costa & Widiger, 2002) describing Neuroticism, Extraversion, Openness...