 8. The Neurobiology of Personality  205
eral frontal cortex (Farr, Hu, Zhang, & Li, 
2012). On the same trials, impulsivity was 
also associated with less functional con -
nectivity between right anterior insula and 
regions of the PFC and visual cortex. One 
reasonable interpretation of these findings is 
that the insula is involved in the generation 
of potentially distracting impulses, whereas 
regions of lateral PFC are involved in re -
straining those impulses.
Potentially in keeping with this interpre -
tation, a DTI study of white matter in 556 
older adults found that conscientiousness 
was positively associated with WM coher -
ence in the uncinate fasciculus, a WM tract 
connecting the insula to frontal regions 
(Lewis et al., 2016). Conscientiousness may 
depend in part on the efficiency with which 
regions of PFC can influence the insula. No -
tably, the association between WM coher -
ence and conscientiousness in this study was 
attributable to variance shared with agree -
ableness and low neuroticism—  that is, to 
the metatrait stability. Given that the behav -
ioral correlates of stability typically involve 
self- control and restraint versus impulsivity, 
it would not be surprising if some of the neu -
ral correlates of conscientiousness are linked 
to the top-down control of emotional or ag -
gressive impulses more generally associated 
with stability (De  Young, 2015; Hirsh, De -
Young, & Peterson, 2009).
Not all brain regions linked to conscien -
tiousness are part of the goal priority net -
work. One additional region that has been 
linked repeatedly to conscientiousness is the 
lateral OFC (Cheetham et al., 2017; Jackson 
et al., 2011; Matsuo et al., 2009; Nouchi et 
al., 2016). The lateral OFC appears to be im -
portant for encoding the contrasting values 
of different outcomes, a function of clear im -
portance for the ability to prioritize different 
goals that seems to be central to conscien -
tiousness (Rudebeck & Murray, 2011).
Finally, conscientiousness, like neuroti -
cism, may be linked to serotonin. In a phar -
macological study, Manuck et al. (1998) 
found that conscientiousness was positively 
associated with serotonergic function in 
men. A similar study failed to replicate this 
effect, but its sample was only half as large 
(Brummett et al., 2008). In a PET study 
( Zientek et al., 2016), serotonin transporter 
availability was correlated with effortful control in dlPFC, OFC, and dorsal ACC, all 
regions that have been implicated in consci -
entiousness.
Agreeableness
Agreeableness  encompasses a variety of 
traits linked to cooperation and altruism. 
As a social species, humans must coordinate 
their goals with those of others, and this co -
ordination is enabled by neural systems that 
process and respond to social information. 
Yet there is obvious variation in the degree 
that individuals are motivated or able to co -
ordinate with others, rather than ignoring 
or exploiting them, and this variation is re -
flected in agreeableness. The two aspects of 
agreeableness are politeness,  which encom -
passes tendencies to follow social rules and 
avoid aggressive or exploitative behavior, 
and compassion,  which encompasses empa -
thy, sympathy, and kindness (De  Young et al., 
2007). Individual differences in agreeable -
ness, therefore, seem likely to reflect varia -
tion in neural systems that orchestrate ag -
gression, inhibitory control, representation 
of the mental states of others (also called 
mentalizing  or theory of mind ), and car -
ing for others emotionally. One study found 
that agreeableness positively predicted per -
formance on a theory-  of-mind test (Nettle 
& Liddle, 2008), and another indicated that 
this association was specific to facets re -
flecting compassion and lack of aggression; 
facets reflecting honesty and unwillingness 
to manipulate others were negatively asso -
ciated with performance on the test (Allen, 
Rueter, Abram, Brown, & De  Young, 2017).
Much of the personality neuroscience re -
search relevant to agreeableness comes from 
the study of empathy, and most measures 
of trait empathy are indicators of compas -
sion (De  Young et al., 2007, 2016), includ -
ing the Empathic Concern subscale (and 
potentially the Perspective Taking subscale) 
of the Interpersonal Reactivity Index (IRI; 
Davis, 1983), the Balanced Emotional Em -
pathy Scale (Mehrabian & Epstein, 1972), 
and the Empathy Quotient (Baron-Cohen & 
Wheelwright, 2004). Research using fMRI 
suggests two general processes involved in 
empathy, one involving the ability to simu -
late and understand the mental states of 