Relationship to Physiology and Health

Research has demonstrated that there is considerable variability across individuals
in their physiological response patterns, both at rest and in response
to various situational stimuli or laboratory manipulations. Evidence indicates
that part of this variability across individuals may, in some cases, be attributable
to certain personality traits or characteristic patterns of behavior.
Furthermore, research suggests that these personality traits may also be related
to the development of psychological or physical disorders. Although
the causal links are not well understood, a growing body of research points
to relations among personality, physiological measures, and psychopathology/
health.

Examples of these relationships are evident in the field of psychopathology,
or the study of abnormal behavior. Hans Eysenck proposed that the
general characteristics of introversion and extroversion lead individuals to
interact very differently with their environment. Some psychophysiological
studies support this notion and suggest that the behaviors characteristic of
these traits may be driven by physiological differences. Anxiety sensitivity
and locus of control are two personality traits that some suggest are related
to the development of anxiety disorders and depression, respectively. To
varying degrees, anxiety disorders and depression have been investigated in
the psychophysiology laboratory and have been found to differentiate individuals with high and low levels of the personality trait, based on their physiological
responses.

Introversion describes the tendency to minimize interaction with the environment;
extroversion is characterized by the opposite behaviors, or the
tendency to interact more with the environment. Eysenck proposed that
such traits reflect physiological differences that are genetically determined
and reflected in the individual’s physiology. Introverted individuals are
thought to be chronically physiologically hyperaroused and thus to seek to
minimize their arousal by minimizing external stimulation. Extroverted individuals
are believed to be chronically physiologically underaroused and to
seek a more optimal level of arousal through increased environmental stimulation.
It should be easy to confirm or disprove such a theory with psychophysiological
studies of resting physiological activity in introverts and extroverts.
Electroencephalograph (EEG) studies have produced contradictory
evidence about the validity of Eysenck’s theory, however; problems in EEG
methodology, experimental design, and measurement of the traits themselves
have led to considerable confusion about whether the traits actually
do have a physiological basis.