Biochemical Factors

"Better biochemical methods of assessment and growing interest in interdisciplinary research in the field of personality research and individual differences will presumably yield more detailed knowledge about the biochemistry of temperament in the near future"

"The most relevant evidence for the cortical arousal theory of Extraversion and Introversion comes from EEG studies since these provide the most direct psychophysiological measure of cortical arousal. The evidence strongly suggests that the cortical augmenting-reducing paradigm is a marker for at least some of the traits in the P (Psychotocism) dimension, particularly disinhibition and impulsivity (p. 133-134).

Zukerman cautions however,

There are many methodological problems in this type of research, like defining the conditions in which to measure tonic arousal. But even when the analysis of literature is limited to the most conceptually and methodologically sound studies...the results are still inconclusive (p. 133).

Because the term temperament has considerable overlap with other dimensions of personality and with emotional and cognitive functions, there are very few studies directed explicitly to the biochemical measurement of tempreament. If, as Netter (1991) suggests, biochemical investigations are based on healthy human subjects, "...they usually start with a trait like extraversion or emotionality and explore the set of biochemical variables most likely associated with this trait (p. 148). In these theories, "...biochemical measures are mainly used for exploration of the psychological construct under investigation with the purpose of elucidating its biological roots" (p. 150).

Netter also notes that modern biological psychiatry also yields,

"...suitable models for extrapolating from psychopathology to normal variations in temperament. One example comes from research by Sulser (1979) in depression where modern biochemical techniques revealed upregulation, i.e., increase in number and sensitivity of beta-receptors in the brain is a major biological change in depression" (p.151).

Benzodiazepine, Serotonin, testosterone, and Monamine Oxidase and their link to temperament have also been investigated. Many theorists have suggested that the neurotransmitter dopamine is the basis of some kinds of general motivational trait involving exploration directed toward primary rewards in animals and novelty and sensation seeking in humans. Aditionally, there are also suggestions of a link to sensation seeking and impulsivity found in the psychoticism dimension (Zukerman, 1991).

Clinical observations of elevated levels of cortisal in some depressed patients, and decreased levels of serotinin metabolite 5-HIAA in cerbrospinal fluid of depressed patients having a history of particularly cruel attempts of suicide led to the theory of genetically low synthesis of serotonin in brain cells in these patients and in psychopaths, alcoholics, and pathological aggressors (Netter, 1991).

As Netter further summarizes, numerous investigators report a great variability in drug response. The underlying basis of which,

"...is of interest to the investigator of temperament, since the detection of sub- or supersensitivity of brain or vascular receptors or of ion channel systems may explain velocity, intensity, and duration of flexibility of behavioral responses...historical attempts to relate temperament to certain diseases like stroke or tuberculosis are revived by, for instance the temperament-related concept of type-A personality (Friedman & Rosenman, 1975) and by the theory that unconscious conflicts may determine the development of predominantly parasympathetically or sympathetically induced diseases" (p. 154).

There also appears to be some relationship, as example between high type-A personality behavior and coping-induced-related myocardial infarction.

Netter concludes that since temperament is that part of a person's psychological characteristic,

"...which is early detectable and genetically determined to a large extent, the search for psychological and biochemical correlates is certainly not altogether useless. Better biochemical methods of assessment and growing interest in interdisciplinary research in the field of personality research and individual differences will presumably yield more detailed knowledge about the biochemistry of temperament in the near future" (p.155).

Validity of biocehmical measures, as noted by Netter, are threatened because,