Trait conscientiousness and the personality meta-trait stability are associated with regional white matter microstructure
Trait conscientiousness and the personality meta-trait stability are associated with regional white matter microstructure
Gary J. Lewis 2
Simon R. Cox 0 1 4
Tom Booth 0 1
Susana Mu n~oz Maniega 0 3 4
Natalie A. Royle 0 3 4
Maria Valde´ s Hernandez 0 3 4
Joanna M. Wardlaw 0 3 4
Mark E. Bastin 0 3 4
Ian J. Deary 0 1
0 Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh , 7 George Square, Edinburgh EH8 9JZ , UK
1 Department of Psychology
2 Department of Psychology, Royal Holloway, University of London , Egham, Surrey TW20 0EX , UK
3 Brain Research Imaging Centre, Neuroimaging Sciences, Centre for Clinical Brain Sciences, University of Edinburgh, Western General Hospital , Edinburgh EH4 2XU , UK
4 Scottish Imaging Network, a Platform for Scientific Excellence (SINAPSE) Collaboration , Edinburgh , UK
Establishing the neural bases of individual differences in personality has been an enduring topic of interest. However, while a growing literature has sought to characterize grey matter correlates of personality traits, little attention to date has been focused on regional white matter correlates of personality, especially for the personality traits agreeableness, conscientiousness and openness. To rectify this gap in knowledge we used a large sample (n > 550) of older adults who provided data on both personality (International Personality Item Pool) and white matter tract-specific fractional anisotropy (FA) from diffusion tensor MRI. Results indicated that conscientiousness was associated with greater FA in the left uncinate fasciculus (b ¼ 0.17, P < 0.001). We also examined links between FA and the personality meta-trait 'stability', which is defined as the common variance underlying agreeableness, conscientiousness, and neuroticism/emotional stability. We observed an association between left uncinate fasciculus FA and stability (b ¼ 0.27, P < 0.001), which fully accounted for the link between left uncinate fasciculus FA and conscientiousness. In sum, these results provide novel evidence for links between regional white matter microstructure and key traits of human personality, specifically conscientiousness and the meta-trait, stability. Future research is recommended to replicate and address the causal directions of these associations.
personality; conscientiousness; stability; white matter microstructure; fractional anisotropy; uncinate fasciculus
Understanding the origins of individual differences in
personality traits has been an enduring challenge for psychologists
(Eysenck, 1967; Gray and McNaughton, 2000; Zuckerman, 2005)
An area of current interest is the association between brain
white matter microstructure and personality traits. Research
has shown links between white matter microstructure and both
neuroticism and (to a lesser extent) extraversion
et al., 2013; McIntosh et al., 2013)
. Less well studied are the other
Big Five personality dimensions: agreeableness,
conscientiousness and openness. This relative lack of attention probably
reflects the clinical orientation of much of the work in this field to
(e.g. Westlye et al., 2011; McIntosh et al., 2013)
, in line with
neuroticism and extraversion (and closely related constructs)
showing strong associations with psychopathology and
wellbeing (Kotov et al., 2010). However, agreeableness,
conscientiousness and openness are important traits in their own right,
with links to a range of important life outcomes
Bogg and Roberts, 2004; Graziano and Tobin, 2013)
therefore deserve further investigation.
To address this gap in knowledge, we sought to advance
understanding regarding links between white matter
microstructure and agreeableness, conscientiousness, and openness
using a large sample of older adults drawn from the Lothian
Birth Cohort 1936 (LBC1936) who completed personality
measures and underwent brain MRI scanning. To capture white
matter microstructure we employed fractional anisotropy (FA)
measured in specific tracts of interest using diffusion tensor
MRI (DT-MRI) and quantitative tractography. We next briefly
summarize research addressing regional white matter
microstructure links with personality, before moving to tests of
association between white matter microstructure and
agreeableness, conscientiousnessand openness in the LBC1936.
Personality and brain white matter microstructure: a brief overview
Broad consensus has now been reached that much variation in
human personality can be understood through five dimensions,
commonly referred to as the Big Five
(John et al., 2008)
agreeableness, conscientiousness, extraversion, neuroticism and
openness. Because there are correlations among the five traits,
two meta-traits are proposed to sit above these five dimensions
(Digman, 1997; DeYoung, 2006)
and a larger number of facets of
each of the dimensions sit at a level below in this hierarchy of
traits (DeYoung et al., 2007). Although interest in the neural
bases of personality traits precedes current thinking regarding
personality trait organization
(e.g. Eysenck, 1967)
neuroimaging technologies, coupled with the broad-based
acceptance concerning the importance of the Big Five as a core model
of personality differences, has led to an increase in efforts
directed towards understanding the neurostructural foundations
of these traits
(DeYoung and Gray, 2009)
Most recently this interest has turned towards examining
brain white matter microstructure correlates of personality,
with FA and mean diffusivity (MD) the most common measures
reported. Higher levels of FA and lower levels of MD are typically
indicative of better white matter microstructure
exception of conditions such as abnormal hypermyelination: e.g.
Moritani et al., 2008)
. There are reported associations between
neuroticism and white matter microstructure, with links to the
uncinate fasciculus—a tract connecting the anterior temporal
lobe with the orbitofrontal cortex
(Catani et al., 2002)
particularly notable. For example,
McIntosh et al. (2013)
, in the
sample of healthy Scottish elderly adults (n > 550) who are also the
participants in this study, observed that FA in the left uncinate
fasciculus was negatively associated with neuroticism
(b ¼ 0.12). Similarly, in a sample of healthy, adult Norwegians
(n ¼ 265), widespread negative associations in FA and positive
associations with MD, including the uncinate fasciculus, have
been reported with neuroticism (Bjørnebekk et al., 2013).
Further, using a sample of 51 healthy adults, neuroticism was
positively associated (r ¼ 0.59) with MD in the left uncinate
fasciculus: while no significant association with FA was found, a
moderate negative association was observed with the left
(r ¼ 0.29: Xu and Potenza, 2012)
. Finally, harm
avoidance, which is in turn highly correlated with neuroticism
(e.g. Jokela and Keltikangas-Ja€rvinen, 2011)
, has also shown
links with FA in the right uncinate fasciculus (r ¼ 0.71) in a
small sample of Italian adolescents
(n ¼ 20; Taddei et al., 2012)
For other Big Five traits the results are less consistent.
McIntosh et al. (2013)
, in addition to the observation of a link
between left uncinate fasciculus FA and neuroticism noted earlier,
reported a positive association with right uncinate fasciculus FA
and extraversion (b ¼ 0.13).
Xu and Potenza (2012)
openness and agreeableness were positively related to FA (rs
from 0.14 to 0.47) and negatively with MD (rs from 0.62 to
0.58) in the corona radiata and superior longitudinal fasciculus
(bilaterally), but observed no links with FA or MD for
extraversion or conscientiousness. In contrast, in a sample of university
students (n ¼ 72),
Jung et al. (2010)
reported that openness was
negatively associated with FA in the right uncinate fasciculus
and anterior thalamic radiation, but no associations were
reported for the other Big Five traits. Of additional note,
Bjørnebekk et al. (2013)
, in a sample of 265 healthy adults,
reported no white-matter associations for Big Five traits other
than neuroticism (as detailed earlier).
More broadly, indirect evidence for associations between
personality and white matter microstructure comes from
studies of groups with personality disorders.
Carrasco et al. (2012)
compared FA in individuals with a borderline personality
disorder (n ¼ 28)—a diagnosis linked with low agreeableness, low
conscientiousness and neuroticism
(Widiger and Costa, 1994)
to FA in a healthy control group (n ¼ 26). Those with a borderline
diagnosis showed lower FA in the left genu and rostral corpus
callosum and in left prefrontal fasciculi, including the anterior
Sundram et al. (2012)
antisocial personality disorder (n ¼ 30: 15 cases, 15 controls)—which in
turn is linked to low agreeableness and low conscientiousness
(Lynam and Widiger, 2001)
—was negatively associated with FA
in several regions, including the genu of the corpus callosum
and the right uncinate fasciculus. Finally,
Mao et al. (2011)
reported that psychoticism measured using the Eysenck
Personality Questionnaire—which is noted to be a combination
of agreeableness and conscientiousness
(e.g. McCrae and Costa,
—was related to FA in the arcuate fasciculus (r ¼ 0.29,
0.36: L/R hemisphere, respectively) in a sample of patients
with epilepsy (n ¼ 65); no significant correlations with
neuroticism or extraversion were observed.
The current study
Beyond neuroticism, relatively little is known regarding brain
white matter microstructure associations with Big Five
dimensions of personality. This observation reflects the fact that only
a handful of studies in this field have been reported to date.
Moreover, most of these studies have been confined to small
(i.e. n < 80, with the exceptions of Bjørnebekk et al.,
2013, McIntosh et al., 2013)
. Here we sought to address this gap
in knowledge. As noted earlier, recent work with the LBC1936
has already examined white matter microstructure links to
neuroticism and extraversion (McIntosh et al., 2013):
accordingly, here we specifically focused on the traits of
agreeableness, conscientiousness and openness. Although results in the
field have been mixed, we made the following predictions based
on the reported associations between these three traits and
white matter microstructure. We hypothesized that there would
be positive links from the corpus callosum genu and uncinate
fasciculus to both agreeableness and conscientiousness in line
with observations in related constructs
(Carrasco et al., 2012;
Sundram et al., 2012)
. We also predicted negative links from the
uncinate fasciculus and anterior thalamic radiation to
openness, in line with findings from Jung et al. (2010). All other
tracttrait analyses were deemed exploratory.
The LBC1936 is a sample (n ¼ 1091) of community-dwelling and
relatively healthy individuals without dementia who, at the
time of being recruited in older age, resided in or close to the
city of Edinburgh (the Lothian region), Scotland. All were born in
1936. Most took part in the Scottish Mental Survey of 1947 in
which they undertook a mental ability test at school on 4 June
1947. They were recruited in older age, at about mean age 70
years, to Wave 1 of a study of cognitive ageing. They have been
extensively followed-up every 3 years during their 70s. Full
details of the study are available in the form of a study protocol
(Deary et al., 2007)
, cohort profile
(Deary et al., 2012)
, and brain
(Wardlaw et al., 2011)
. The data from the
LBC1936 cohort used in this study were obtained at Wave 2 of
the study, when the participants had a mean age of about 73
years. This was the first wave in which brain imaging was
performed. Participants travelled to the Wellcome Trust Clinical
Research Facility in Edinburgh for testing. The study was
approved by the Lothian (REC 07/MRE00/58) and Scottish
Multicentre (MREC/01/0/56) Research Ethics Committees and all
subjects gave written informed consent.
Big Five personality traits were measured using the
wellcharacterized and validated International Personality Item Pool
(IPIP) 50-item inventory
(Goldberg, 1999; Gow et al., 2005)
10 items each tapping emotional stability (the opposite of
neuroticism), extraversion, intellect (similar to openness),
agreeableness and conscientiousness. Participants rated each
self-description on a 1 (very inaccurate) to 5 (very accurate)
History of stroke, hypertension, and cigarette use
At Wave 2, participants gave self-reported information on
history of stroke, hypertension and cigarette use as part of a
medical interview. We used these as covariates in our analyses, as
all are linked to brain white matter microstructure damage
Gons et al., 2011; Staals et al., 2014; Wardlaw et al., 2014)
. All were
coded as a binary variable. Stroke was coded as 0 ¼ no
self-report of stroke, and 1 ¼ self-report of stroke. Hypertension was
coded as 0 ¼ no, and 1 ¼ yes. Cigarette use was coded as
0 ¼ never smoked, and 1 ¼ current or past smoker.
Brain white matter tract microstructure
Diffusion MRI was performed using a GE Signa HDXt 1.5-T
clinical scanner (General Electric, USA) using a self-shielding
gradient set with maximum gradient strength of 33 mT m 1, and a
manufacturer-supplied eight-channel phased-array head coil.
Single-shot, spin-echo echo-planar imaging diffusion-weighted
volumes (b ¼ 1000 s mm 2) were acquired in 64 non-collinear
directions, along with seven T2-weighted volumes (b ¼ 0 s
mm 2). Seventy-two contiguous axial slices of thickness 2 mm
were acquired with a field of view of 256 256 mm and matrix
size of 128 128, giving a resolution of 2 2 2 mm. The
repetition time was 16.5 s and echo time 95.5 ms. The total scan time
was 20 min
(see Wardlaw et al., 2011 for details of the full
Diffusion MRI data were converted into NIfTI (http://nifti.
nimh.nih.gov/nifti-1) format. Pre-processing steps were
performed using the tools provided in FSL (FMRIB, Oxford, UK;
www.fmrib.ox.ac.uk) to extract the brain, remove bulk motion
and eddy current induced artifacts and estimate water DT
parameters. Brain connectivity data were created using the
BEDPOSTX/ProbTrackX tractography algorithm with a two-fiber
model and 5000 streamlines to reconstruct tracts of interest.
An automatic tract selection method—probabilistic
neighbourhood tractography (PNT)—with good reproducibility
(Clayden et al., 2009a)
, based on a model of tract topology
(Clayden et al., 2007), was used to generate equivalent tracts of
interest in each participant. PNT, which was implemented in
the TractoR package (http://www.tractor-mri.org.uk), optimizes
the choice of seed point for tractography by estimating the best
matching tract from a series of candidate tracts generated from
a neighbourhood of voxels (7 7 7) placed around a voxel
transferred from standard space against a pre-defined reference
tract. The topological tract model was also used to reject any
false positive connections
(Clayden et al., 2009b)
. As a
consequence, this procedure significantly improved tract
segmentation. Twelve white-matter tracts were segmented: the genu and
splenium of corpus callosum, cingulum bundles, anterior
thalamic radiations, uncinate, arcuate and inferior longitudinal
fasciculi. For each subject, the seed point that produced the best
match tract to the reference for each of the 12 pathways was
determined, with the resulting tractography mask applied to
each participant’s FA volume. Tract-averaged FA values were
calculated from these masks and used in all subsequent
analyses. In order to make sure that the segmented tracts were
anatomically plausible representations of the tracts of interest, a
researcher (S.M.M.) visually inspected all masks blind to the
other study variables and excluded tracts that showed aberrant
or truncated pathways.
Of the 866 LBC1936 participants who attended Wave 2 testing,
668 (males ¼ 53%) individuals provided usable tractography data
which passed the visual quality control procedures outlined
earlier. The range of available data was from a low of n ¼ 556 for
the left anterior thalamic radiation to a high of n ¼ 664 for the
right inferior longitudinal fasciculus.
We first tested for association between white matter
microstructure, as assessed by tract-averaged FA, and the traits
agreeableness, conscientiousness, and openness. For hypothesized
white-matter-personality links, our nominal level for statistical
significance was P < 0.05. These results are detailed in full in
Table 1. For all other associations, we used a false discovery rate
(FDR) corrected P-value
(Benjamini and Hochberg, 1995)
results are detailed in full in Table 2. Additional analyses using
alternative measures of the Big Five traits (i.e. NEO-FFI traits
measured at age 70, and thus collected 3 years prior to the
diffusion MRI, and a mean score for each dimension derived from
the NEO-FFIage70 and IPIPage73) are reported in the
Supplementary Materials. These subsidiary results are mostly
unchanged from those reported below, with all key results
As predicted, we observed significant positive associations
between uncinate fasciculus FA bilaterally with
conscientiousness (r ¼ 0.17/.09; P ¼ 0.00005/.03, L/R hemisphere, respectively:
also see Supplementary Figure S1), left uncinate fasciculus FA
with agreeableness (r ¼ 0.13; P ¼ 0.002), and right anterior
thalamic radiation FA with openness (r ¼ 0.09; P ¼ 0.03).
Our exploratory analyses revealed significant associations
between conscientiousness and FA measured in bilateral
cingulum (r ¼ 0.13/.14; P ¼ 0.009/0.008, L/R hemisphere, respectively),
inferior longitudinal fasciculus (r ¼ 0.10; P ¼ 0.03; r ¼ 0.13;
P ¼ 0.009, L/R hemisphere, respectively), left arcuate fasciculus
(r ¼ 0.12; P ¼ 0.02) and right anterior thalamic radiation (r ¼ 0.12;
P ¼ 0.01). Agreeableness was significantly associated with FA in
left inferior longitudinal fasciculus (r ¼ 0.10; P ¼ 0.03).
In order to establish whether the observed associations were
specific to individual tracts, or reflected more generalized tract
(see Booth et al., 2014)
, we next examined whether the
above associations were robust when controlling for mean tract
integrity. To this end we took a mean score of tract integrity,
excluding the tract of interest for any given analysis, and used
this score as a control variable. Not all individuals had usable
data for each of the 12 tracts; as such, we used only individuals
who had 10 or more of the tracts available for analysis. Left
uncinate fasciculus (b ¼ 0.12, P ¼ 0.03) remained an independent
predictor of conscientiousness when controlling for mean tract
integrity (left uncinate fasciculus was correlated with mean
tract integrity r ¼ 0.62, P < 0.001). Moreover, this association was
almost unchanged when additionally controlling for history of
stroke, hypertension, and smoking. However, the other
significant associations between FA and personality fell below
nominal significance when controlling for mean tract integrity.
Mean tract integrity was associated with agreeableness (r ¼ 0.10,
P ¼ 0.01) and conscientiousness r ¼ 0.18, P < 0.001, but not with
openness r ¼ 0.06, P ¼ 0.12)
(see also Booth et al., 2014)
. Finally, in
line with the association between openness and general
(Ashton et al., 2000)
we also examined whether openness
was associated with white-matter microstructure when
controlling for general intelligence (defined here as the first unrotated
principle component from six WAIS III tests: this component
accounted for 51% of the test score variance); however, the pattern
of correlations was virtually unchanged to those reported
earlier and no significant observations were noted.
The positive link between left uncinate fasciculus FA and
both conscientiousness and agreeableness (albeit with the latter
not significant when controlling for mean tract integrity),
alongside an association with neuroticism as reported in previous
work in this sample
(McIntosh et al., 2013)
, gives rise to the
possibility that the personality link with this tract is better
represented at the meta-trait level. Specifically, a body of work has
indicated that covariation between agreeableness,
conscientiousness and neuroticism can be understood as a higher-order
latent factor commonly termed ‘stability’
(DeYoung, 2006; also
see Digman, 1997)
. To test for this possibility we used a
structural equation modelling approach using Amos version 22
(Arbuckle, 2013). This analysis indicated that the higher-order
latent factor of stability was significantly associated with left
uncinate fasciculus FA (b ¼ 0.27, P < 0.001: see Figure 1, Panel A).
This association remained significant (b ¼ 0.21, P < 0.001) when
controlling for mean tract integrity (see Figure 1, Panel B: note,
neuroticism/emotional stability and mean tract integrity were
correlated r ¼ 0.09, P ¼ 0 .02). We also tested whether variation
in agreeableness, conscientiousness, and
neuroticism/emotional stability (i.e. the residual variance for each of these traits),
over and above the stability factor, showed links to left uncinate
fasciculus FA. No such links were observed (all bs < 6 0.02, all
Ps > 0.88) indicating that left uncinate fasciculus’s link to
personality is most parsimoniously understood at the meta-trait
This study used a relatively large sample (n > 550) of older adults
to examine links between regional white matter microstructure
and several core dimensions of personality: specifically,
agreeableness, conscientiousness and openness. Several key results
were noted. First, we observed a positive link between left
uncinate fasciculus FA and conscientiousness. We also noted a
positive association between left uncinate fasciculus FA and
agreeableness (although this association fell below nominal
significance when controlling for mean tract integrity). These
associations, coupled with recent work highlighting a negative link
between neuroticism and left uncinate fasciculus FA
et al., 2013)
, led us to examine whether the common factor
accounting for shared variance in agreeableness,
conscientiousness and neuroticism/emotional stability—stability
2006; also see Digman, 1997)
—was associated with left uncinate
fasciculus microstructure. This additional analysis highlighted
the fact that the personality meta-trait of stability was the most
parsimonious level at which to account for associations
between individual personality traits and the left uncinate
fasciculus; i.e. the associations between this tract and
agreeableness, conscientiousness or neuroticism/emotional stability
were mediated by stability.
Is this association between stability and the left uncinate
fasciculus plausible? Stability is argued to reflect the ‘need to
maintain a stable organization of psychosocial function’
and thus would likely be dependent on
neural systems instantiating impulse control, emotion
regulation and related cognitive-affective processes. The uncinate
fasciculus is a major connection between anterior temporal and
ventral prefrontal regions of the brain. Social-cognitive abilities
are associated with both orbitofrontal and anterior temporal
(MacPherson et al., 2015; Olson et al., 2013)
characteristics in left uncinate fasciculus (Jalbrzikowski et al.,
2014) and with neuroticism and agreeableness
(e.g. Nettle and
; thus the uncinate fasciculus appears to be ideally
placed to modulate these personality traits and related
(Cardinal et al., 2002)
Specific recommendations for future research are
warranted. First, we were only able to explain a modest proportion
of personality trait variation via the white matter tract
microstructure measures examined here, and previous research
Xu and Potenza, 2012)
has identified white matter
microstructure links to personality in tracts not investigated in this study.
The modest effects observed here thus likely reflect the fact
that multiple brain regions and neuroanatomical components
(e.g. white matter microstructure, regional cortical thickness)
collectively account for individual differences in personality.
Future work, then, should seek to extend on the scope of the
current observations in order to more fully characterize the
neuroanatomical bases of personality. Second, with the
crosssectional design employed here we are not able to determine
the direction of causality underlying the observed relationships
between white matter microstructure and personality. In this
sample of older adults it is conceivable that individual
differences in brain structure personality lead to personality trait
variation, or that personality leads to changes over time in brain
structure, or both. The latter perspective is somewhat mitigated
by our key results robust when controlling for the effects of
mean tract integrity. Nonetheless, future work utilizing
longitudinal studies of brain development and change could contribute
to understanding the direction of causal influences underlying
(Hedman et al., 2012)
In summary, we provide evidence from a relatively large
sample of older adults that core aspects of
personality—specifically conscientiousness and the meta-trait of stability—are
associated with regional white matter microstructure;
specifically, left uncinate fasciculus. Future research is recommended
in order to establish the causal direction of this association, as
well as to characterize more fully the neuroanatomical bases of
We thank the members of the LBC1936 who participated in
this study, radiographers at the Brain Research Imaging
Centre, and the LBC1936 research associates who collected
and entered some of the data used in this article.
This research was supported by Research Into Ageing and
continues as part of The Disconnected Mind project, funded
by Age UK. Magnetic Resonance Image acquisition and
analyses were conducted at the Brain Research Imaging Centre,
Neuroimaging Sciences, University of Edinburgh (www.bric.
ed.ac.uk) which is part of SINAPSE (Scottish Imaging
Network—A Platform for Scientific Excellence) collaboration
(www.sinapse.ac.uk) funded by the Scottish Funding
Council and the Chief Scientist Office. This work was
undertaken within The University of Edinburgh Centre for
Cognitive Ageing and Cognitive Epidemiology (www.ccace.
ed.ac.uk), part of the cross council Lifelong Health and
Wellbeing Initiative (MR/K026992/1), for which funding from
the BBSRC and MRC is gratefully acknowledged.
Supplementary data are available at SCAN online.
Conflict of interest. None declared.
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