On the biological determination of personality structure

The controversy surrounding two particular problems has stymied the development of a consensus view concerning the structure of personality. First, there has been disagreement concerning the ‘independence’ of introversion-extraversion and measures of neuroticism. The other problem concerns the ‘duality’ of introversion-extraversion and whether it is even useful to retain this concept when it may only represent a ‘shotgun wedding’ of ‘sociability’ and ‘impulsivity’. Recent findings are discussed which relate to the neurophysiological underpinnings of personality. It is suggested that these findings, and the associated model, lie outside the circulus vitiosus of factor analysis and therefore that they provide a basis for resolving the independence and duality issues. It is argued that the tendency for introversion-extraversion to correlate with neuroticism only reflects a degree of coincidence and not equivalence. The psychological coincidence is conceived as resulting from the anatomical linkage of different neurophysiological subsystems which provide the substrata for the two personality dimensions. It is also argued that the ‘sociability’ and ‘impulsivity’ duality relates to distinct ‘sensitivity’ and ‘synergistic’ aspects of thalamocortical arousability. These distinct arousability dimensions nevertheless both contribute to the effectiveness of descending inhibitory projections that act on the brain-stem reticular formation and hence determine introversion-extraversion differences. In this scheme of things the three psychological dimensions are different but again there are anatomical linkage correlations reflecting coincidence rather than equivalence.