Psychoticism/Impulsivity/Sensation Seeking/Conscientiousness/Constraint 99augmenting pattern were active, exploratory, and approached
rather than withdrew from novel stimuli. Augmenting cats
adapted easily to novel situations, were responsive to a sim-
ple reward task, but were poor at learning to inhibit responses
where they were only reinforced for low rates of response
(Hall, Rappaport, Hopkins, Griffin, & Silverman, 1970;
Lukas & Siegel, 1977; Saxton, Siegel, & Lukas, 1987).
Siegel extended this paradigm to a study of two geneti-
cally selected strains of rats, one actively avoidant or more
aggressive and the other passive and frozen in reaction to
shock (Siegel, Sisson, & Driscoll, 1993). The first strain
consistently showed the augmenting EP pattern, and the sec-
ond showed the reducing. Other behavioral characteristics of
these strains were consistent with the human model of im-
pulsive sensation seeking: The augmenting strain was ag-
gressive, more willing to ingest alcohol, had high tolerance
for barbituates, and self-administered higher intensities of
electrical stimulation in reward areas of the limbic brain than
the reducing strain.
Biochemical reactions suggested the basis for behavioral
differences in characteristics of stress-reactive neurotransmit-
ter and hormonal responses. Under stress, the augmenting
strain showed more dopaminergic activity in the prefrontal
cortex of brain, whereas the reducers had a stronger reaction in
the hypothalamic-pituitary-adrenal cortex (HYPAC) stress
pathway including increased serotonergic activity and corti-
cotropin releasing factor in the hypothalamus and adrenocor-
ticotropic hormone in the pituitary gland. Dopamine is a
neurotransmitter implicated in action tendencies and theo-
rized to be the basis of novelty and sensation seeking.
Dopamine release would explain the active avoidance patterns
that were the basis for selecting the two strains. Conversely,
serotonin activity is associated with behavioral inhibition.
Monoamines
The animal model described earlier suggests that sensation
seeking and related traits in humans may be associated posi-
tively with dopaminergic and negatively with serotonergic
reactivity. Indirect evidence of this association comes from
patients with Parkinson’s disease (PD), in which dopamine is
depleted 75% in ventral tegmental neurons. A study of per-
sonality of PD patients showed that the PD patients were sig-
nificantly lower on novelty seeking than controls but did not
differ from them on harm avoidance or reward dependence
(Menza, Golbe, Cody, & Forman, 1993). The PD patients
were more depressed than controls, but depression did not
correlate with novelty seeking scores.
Simple correlations between sensation seeking and
dopamine and serotonin metabolites (HVA and 5-HIAA)
assayed from CSF reveal no correlations between these
metabolites and sensation seeking or the P scale or impulsiv-
ity scales (Ballenger et al., 1983; Limson et al., 1991). How-
ever, the correlational study by Ballenger et al. found a
significant negative correlation between norepinephrine in
the CSF and sensation seeking. A significant correlation was
found between P and dopamine D2 binding in left and right
basal ganglia in a PET study of a small group of normal sub-
jects (Gray, Pickering, & Gray, 1994).
An experimental study by Netter, Hennig, and Roed
(1996) used drugs that stimulate (agonist) or inhibit (antago-
nist) activity in the serotonergic and dopaminergic systems
and measured their effects on hormonal, emotional-state, and
behavioral reactions. Their findings suggested a low respon-
sivity of the serotonergic system in high sensation seekers,
but no association of dopaminergic response to an agonist and
sensation seeking. However, craving for nicotine was in-
creased by a dopamine agonist in high sensation seekers, sug-
gesting that dopamine stimulation may induce more approach
behavior in high than in low sensation seekers. Experiments
in which nicotine or amphetamine is given to participants
high or low in sensation seeking or novelty seeking showed
that the high sensation/novelty seekers had more intense
“highs” or subjective effects in response to these drugs than
did low sensation seekers (Hutchison, Wood, & Swift, 1999;
Perkins, Wilson, Gerlach, Broge, & Grobe, 2000). The effect
for nicotine was most intense for nonsmokers, and the study
on amphetamine did not use persons with a drug history.
These special reactions of high sensation/novelty seekers to
the novel drugs suggests some sensitivity to these dopamine
agonists, perhaps in the receptors.
Another study by the German group found that the disin-
hibition type of sensation seeking and impulsivity, as well as
aggression, were correlated with a response to a serotonin
antagonist indicating low serotonergic responsivity in impul-
sive sensation seekers (Hennig et al., 1998).Monoamine OxidaseFairly consistent negative relationships have been found be-
tween sensation seeking and MAO. A survey of results in 1994
showed low but significant negative correlations between
platelet MAO and sensation seeking trait in 9 of 13 groups,
and in 11 of 13 groups the correlations were negative in sign.
The gender and age differences in sensation seeking are con-
sistent with the gender and age differences in MAO described
previously. Low MAO levels are characteristic of disorders
characterized by impulsive, antisocial behavior including an-
tisocial and borderline personality disorders, alcoholism and
heavy drug abuse, pathological gambling disorder, bipolar