Chapter 14 Eysenck’s Biologically Based Factor Theory 427in the brain involved in emotion and motivation, primarily the amygdala and hypo-
thalamus. Therefore, researchers have explored Eysenck’s hypothesis that differ-
ences in limbic system activity and physiology are the basis for neuroticism—the
disposition to experience negative emotions such as stress, anxiety, guilt, and
depression. In general, there is quite a bit of empirical evidence supporting this
theory.
For instance, Mincic (2015) conducted a meta-analysis on the topic of neu-
roticism and the structure and function of the amygdala. Meta-analyses are the pro-
cess of collecting all of the published and even as much unpublished literature as
one can find on one specific topic or question and calculating the overall size of the
effect on the question at hand. It is a quantitative review of the literature and tells
us how large of an effect there is across all studies rather than just one. Mincic col-
lected and analyzed 13 quantitative studies on brain structure and function and neu-
roticism. Across these 13 studies, there was consistent evidence for more grey
matter (cell bodies) in the amygdala of people high in neuroticism compared to those
who were low in neuroticism. More grey matter is consistent with increased activity
or responsiveness of the amygdala. To be fair, this association is not true for each
amygdala. Like all subcortical structures the amygdala come in twos: one in the right
hemisphere and one in the left. Increased amygdala activity is found more in the left
than right amygdala (Mincic, 2015). Other research suggests that there are reduced
neural connections between the amygdala and other brain regions involved in control-
ling thoughts. This lack of connection appears to inhibit the “off switch” in the
amygdala resulting in its over activity to negative experiences (Canli, 2008; Ormel
et al., 2012). In short, people high in neuroticism are biased toward and more sensi-
tive to negative emotional experiences partly due to an overactive amygdala.
Increased physiological reactivity—as seen in sweating—is also associated
with neuroticism. In one study, for example, 169 adults (mean age of 27) had their
physiological responses measured as they watched a 60-minute TV program (House)
(Brumbaugh, Kothuri, Marci, Siefert, & Pfaff, 2013). This TV episode was chosen
because it included four separate 1-minute scenes that have been demonstrated to
portray strong negative emotions (violence-fear, sadness, tension, and threat-hostility).
Participants wore a vest that continuously measured heart-rate, skin conductance
(sweating), and respiration (breathing). They also completed a short 10-item measure
of personality (Gosling et al., 2003). Inspired by Eysenck’s theory, Brumbaugh and
colleagues predicted that people high in neuroticism would have greater physiologi-
cal response to each of the four negative emotion scenes. They found partial support
for these predictions in that the violent-fear scene produced greater galvanic skin
conductance (sweating) in people high in neuroticism than those low in it. Heart rate
and respiration differences, however, did not exist. Other research reported that
greater skin conductance reactivity in people with high compared to low levels of
neuroticism peaked at 4–5 seconds after the negative stimulus and did not return to
normal for about 9 seconds (Norris, Larsen, & Cacioppo, 2007). In those low in
neuroticism, however, the peaks were small and occurred at about 2 seconds after
the stimulus and reactivity was back to normal by 3–4 seconds after the stimulus.
So the reactivity is both stronger and longer lasting in people high in neuroticism.
In sum, the current research on the biology of neuroticism supports Eysenck’s
theoretical ideas going back to the 1960s, namely that the differences in limbic