 8. The Neurobiology of Personality  203
and regions of dlPFC. Extraversion, in con -
trast, was associated with connectivity be -
tween the dopaminergic region and the nu -
cleus accumbens and caudate nucleus (and 
only during rest). Because the dlPFC plays 
an important role in voluntary attention, 
this finding suggests more dopaminergically 
driven attention to sensory stimuli in people 
high in O/I and may help to explain their 
heightened curiosity and pleasure in sensory 
experience.
Much of the dlPFC is part of a broader 
neural network known as the cognitive con -
trol or frontoparietal network,  which ap -
pears to be crucial for intelligence and work -
ing memory (Jung & Haier, 2007; Vincent, 
Kahn, Snyder, Raichle, & Buckner, 2008). 
Working memory  is the voluntary mainte -
nance and manipulation of information in 
short-term memory and appears to be the 
most important cognitive function contribut -
ing to intelligence (Conway, Kane, & Engle, 
2003). This network is likely to be crucial 
for intellect, and one fMRI study found that 
intellect (but not openness) predicted neural 
activity in regions of this network during a 
working memory task (De  Young, Shamosh, 
Green, Braver, & Gray, 2009). Specifically, 
these were regions of PFC in which neural 
activity was associated with accurate work -
ing memory performance, which was also 
correlated with intellect but not openness.
Whereas the frontoparietal network is 
likely to be most relevant to intellect specifi -
cally, another of the brain’s major networks 
is likely to be important for O/I more broad -
ly. This is the so-  called “default network,” 
which was discovered fortuitously as a set 
of regions that were more active during rest 
than during various cognitive tasks (includ -
ing working memory tasks). Later, however, 
certain tasks (e.g., episodic memory tasks) 
were shown to activate this network reliably 
(Andrews-  Hanna, Smallwood, & Spreng, 
2014). Its functions have been described in 
terms of “self-  generated thought,” and many 
of them involve imagination or simulation in 
one form or another. Imagining the past, the 
future, or any hypothetical scenario requires 
the default network, making it a promising 
candidate as a substrate of O/I (De  Young, 
2015). In a recent functional connectivity 
study, Beaty et al. (2016) explicitly tested 
this hypothesis in two independent samples and showed that efficiency of information 
processing among the core regions of the de -
fault network was positively associated with 
O/I.
The majority of reasonably large structur -
al MRI studies have found no association be -
tween O/I and measures of regional volume, 
cortical area, or cortical thickness (Bjørne -
bekk et al., 2012; De  Young et al., 2010; Liu 
et al., 2013). However, in the largest such 
study to date ( N = 507), Riccelli et al. (2017) 
detected a number of associations between 
O/I and cortical morphometry. O/I was as -
sociated with decreased cortical thickness 
(but increased surface area) in the postcen -
tral sulcus of the parietal lobe, which is simi -
lar to the findings of a longitudinal study re -
porting that volume loss in a similar parietal 
region was linked to increases in O/I (Taki 
et al., 2013). This parietal region appears to 
be part of the frontoparietal network impli -
cated in working memory, as do several of 
the other regions where Riccelli et al. (2017) 
found associations of cortical morphometry 
with O/I, in the dlPFC and cingulate cortex. 
Several other associations were detected in 
the occipital lobe, which is largely respon -
sible for vision; this seems congruent with 
the heightened sensory awareness associated 
with openness.
Evidence for a neural correlate specific 
to openness rather than intellect is emerg -
ing from studies of white-  matter structure. 
White matter  (WM) refers to the bundles 
of axons that connect different parts of the 
brain, and the coherence of these bundles 
or tracts can be assessed using a form of 
MRI called diffusion tensor imaging (DTI). 
Several DTI studies have examined the as -
sociation of O/I with WM coherence with 
apparently conflicting results. One found 
a positive association of O/I with WM co -
herence in the frontal lobes (Xu & Potenza, 
2012), another found no association (Bjør -
nebekk et al., 2013), and yet another found 
a negative association (Jung, Grazioplene, 
Caprihan, Chavez, & Haier, 2010). What 
distinguished the third of these from the 
other two is that Jung et al. controlled for 
IQ, which is positively correlated with WM 
coherence throughout much of the brain 
(Chiang et al., 2009; Grazioplene Chavez, 
Rustichini, & De  Young, 2016; Penke et al., 
2012). Because O/I is associated with IQ, 