Introduction: neuropsychological approaches to personality

In this chapter we discuss the hypothesis that personality is an expression of individual differences in brain function. There are several reasons for linking personality traits to neural systems. First, there is the evidence from behaviour genetics discussed in the last chapter. If personality traits are partially inherited, then there must necessarily be a biological influence on traits, encoded within the person's DNA. Of course, the influence of the genotype on brain physiology is likely to be influenced by interaction with the environment. Second, there is striking evidence for radical personality change resulting from brain damage (see Powell, 1981; and Zuckerman, 1991, 1999 for reviews). Damage to the frontal lobes of the cerebral cortex is notorious for disruption of personality; the person may become unstable, impulsive and even aggressive (depending on the exact region damaged). Third, there is evidence that traits correlate with psychophysiological indicators of brain functioning, such as the electrical activity of the brain and the increase in heart rate when the person is exposed to stress. Such observations suggest that we might develop neuropsychological theories of personality traits. Such theories should describe how individual differences in the functioning of specific brain systems influence individual differences in behaviour.

However, there are various difficulties involved in building a neuropsychological theory of personality traits. First, the complexity of the task is daunting.