A working scheme and other relevant traits

All the evidence seems consistent with previous research in animals, which has shown that Brattelboro rats (a genetically defective line lacking the vasopressin receptor gene) are less fearful, more aggressive, and less prone to forming strong infant-mother bonds, (3Z> and that in the two Roman rat lines selectively bred for differential fearfulness RHAs are more aggressive and more avid incentive-seekers then their RLA counterparts. (35) Thus temperamental styles in animals show differential clustering of behavioural traits, which correspond to specific (and complex) neurohormonal profiles. Sometimes a specific genetic modification is sufficient to promote a fully differentiated temperament, as in the case of the mice lacking a-CaMKII mentioned above(54) (Table 1).

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Table 1 Summary of behavioural phenotypes in a-CaMKII mutant mice

It is possible that this may also hold for particular temperamental clusters in humans. However, we have already established that, when trying to explain the genetic contribution to basic ('universal') personality traits, a multigenic/interactional approach was necessary to explain just part of the measured variance in each trait. Nevertheless, this contribution can be very important, as most of the systematic research involving twins has yielded estimates of just over 40 per cent for the genetic input to typical personality traits, with modest estimations of around 7 per cent assignable to the so-called shared (familial/cultural) environment. (!°>60,)

Despite this, non-shared environmental influences (from the womb onwards) and genetic-environmental interactions make a well-known contribution to each individual temperament/6!,6.2) These complex influences may act first by modelling the development of basic neuroendocrine regulatory systems that cope with both natural and social challenges, and second by shaping the neurocognitive architecture that results in an autonomous and particular lifestyle. An interactional approach along these lines is now laying the foundation for a better description of the different factors that contribute to building the typical profiles of normal or abnormal personalities.

Such a general scheme must include other factors, in addition to the basic ones considered so far. For instance, the recent detection of a substantial genetic contribution to the baseline level of happiness,(63) which all individuals show throughout life independently of the events or episodes that they encounter, must be important for personality diagnoses, because such a 'calibration point' has a direct relationship with the affective tone of optimism or pessimism. (1. 64,)

Moreover, other traits and measures in the domain of cognitive performance (e.g. attention spans and oscillations, perceptual/appraisal reliability, typical thinking styles, and memory biases) or of character (e.g. religiosity/transcendence, conservatism, self-directness/self-esteem, and the drive to achieve/enthusiasm) should be incorporated into the whole description of personality structure. This is essential if the aim is to produce a general framework powerful enough to contain the complex categories that clinicians have tried to construct on the basis of systematic observation for more than a century. Cloninger (!, 6 ,6,6,) has advanced a proposal along these lines, which may function as an initial useful step to guide future work.

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