Amygdala activation in the processing of neutral faces in social anxiety disorder: is neutral really neutral?

Abstract

Previous research has suggested that Social Anxiety Disorder (SAD) is associated with a tendency to interpret ambiguous social stimuli in a threatening manner. The present study used event-related functional magnetic resonance imaging to examine patterns of neural activation in response to the processing of neutral facial expressions in individuals diagnosed with SAD and healthy controls (CTLs). The SAD participants exhibited a different pattern of amygdala activation in response to neutral faces than did the CTL participants, suggesting a neural basis for the biased processing of ambiguous social information in SAD individuals.

Full text

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Brief report
Amygdala activation in the processing of neutral faces in social
anxiety disorder: Is neutral really neutral?
Rebecca E. Cooney⁎, Lauren Y. Atlas, Jutta Joormann, Fanny Eugène, Ian H. Gotlib
Department of Psychology, Bldg. 420, Jordan Hall, Stanford University, Stanford, CA 94305, United States
Received 26 January 2006; received in revised form 3 May 2006; accepted 10 May 2006
Abstract
Previous research has suggested that Social Anxiety Disorder (SAD) is associated with a tendency to interpret ambiguous social
stimuli in a threatening manner. The present study used event-related functional magnetic resonance imaging to examine patterns of
neural activation in response to the processing of neutral facial expressions in individuals diagnosed with SAD and healthy controls
(CTLs). The SAD participants exhibited a different pattern of amygdala activation in response to neutral faces than did the CTL
participants, suggesting a neural basis for the biased processing of ambiguous social information in SAD individuals.
© 2006 Elsevier Ireland Ltd. All rights reserved.
Keywords: Amygdala; Social phobia; Social anxiety disorder; Functional magnetic resonance imaging (fMRI)
1. Introduction
Social Anxiety Disorder (SAD) is a prevalent and
debilitatingdisordercharacterizedbyintensefearofsocial
situationsthatsignificantlyimpairsqualityoflife(Cramer
et al., 2005). Negatively biased processing of social
information has been posited to play a critical role in this
disorder; indeed, individuals diagnosed with SAD have
been found to have better memory for critical than for
accepting faces (Lundh and Ost, 1996) and to selectively
attend to negative faces and other threatening social
stimuli (Amir et al., 2003; Clark and McManus, 2002).
Recently, investigators have begun to examine the
neurobiological bases of the processing of social stimuli
in SAD and have found that individuals with SAD
exhibit elevated activation to negative faces (specifically
anger and disgust) in the anterior cingulate cortex,
insula, parahippocampal gyrus, and amygdala when
their responses are contrasted with activations to neutral
faces (Straube et al., 2004; Amir et al., 2005). In inter-
preting these findings, researchers have suggested that,
in particular, amygdala activation to threatening social
stimuli plays an important role in SAD (Phan et al.,
2006; Stein et al., 2002). It is important to note, how-
ever, that behavioral studies suggest that participants
with SAD are likely to interpret neutral and other
emotionally ambiguous facial expressions negatively
(Winton et al., 1995). This is consistent with brain ima-
ging studies that demonstrate that individuals diagnosed
with SAD, compared with control participants, exhibit
different patterns of amygdala activation when pre-
sented with neutral faces that are paired with an aversive
stimulus (Birbaumer et al., 1998; Schneider et al., 1999;
Veit et al., 2002). Given these behavioral and imaging
finding indicating that SAD individuals may perceive
Psychiatry Research: Neuroimaging 148 (2006) 55–59
www.elsevier.com/locate/psychresns
⁎Corresponding author. Fax: +1 650 725 5699.
E-mail address: rcooney@psych.stanford.edu (R.E. Cooney).
0925-4927/$ - see front matter © 2006 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.pscychresns.2006.05.003

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neutral faces as threat-related, it is critical to assess the
neural responses of SAD individuals to neutral faces
alone. Indeed, the possibility that SAD participants are
characterized by threat-related neural activations to
neutral faces would have important implications for
how one interprets results of contrasts of activations to
negative versus neutral faces. The present event-related
functional magnetic resonance imaging (fMRI) study
was designed to examine whether SAD participants
exhibit activation to neutral faces in areas of the brain
that have been found to be associated with the pro-
cessing of negative faces. Specifically, we hypothe-
sized that individuals diagnosed with SAD, compared
with nonpsychiatric controls, would exhibit increased
amygdala activation in response to neutral faces
versus an oval fixation and that the strength of
amygdala activation within the group of SAD partici-
pants would be correlated with level of state and trait
anxiety.
2. Methods
2.1. Participants
Ten participants with SAD (mean age=28.7 years, S.
D.=8.46; 6 female; all right-handed) and ten healthy
control participants (CTL; mean age=28.8 years, S.D.
=5.33; 7female, 9right-handed) were recruited from the
Department of Psychiatry at Stanford University and
from the community. Participants were diagnosed using
the Structured Clinical Interview for DSM-IV (First et
al., 1996). Nine of the ten SAD participants received a
diagnosis of Generalized Social Anxiety Disorder. SAD
participants were excluded if they had comorbid Major
Depressive Disorder or Panic Disorder, or if they repor-
ted alcohol or substance abuse symptoms in the last
6 months; we did not exclude SAD participants for
lifetime Axis-I comorbidity. Control participants were
free of current or lifetime diagnoses of any Axis-I dis-
order. Five of the ten SAD participants were taking
selective serotonin reuptake inhibitors (or Wellbutrin) at
the time of scanning. All participants were fluent in
English and free of head trauma. Participants completed
theState-Trait Anxiety Inventory (STAI),State (STAI-S)
and Trait (STAI-T) versions (Spielberger et al., 1970),
immediately before being scanned.
2.2. Procedure
Color stimuli were selected from the MacArthur
Network Face Stimuli Set (http://www.macbrain.org/
faces/index.htm). Fearful, happy, sad, angry, and neutral
faces from 20 actors, and an oval with a cross-hair in the
middle that was the same size as the actors' faces, were
presented in the scanner in an event-related design
(because of the specific question being addressed in the
present study, only the neutral faces and the oval figures
are compared here). Each actor's neutral pose was
presented no more than four times over the course of the
experiment. Participants were instructed to use a button
box to make valence ratings (negative, neutral, or
positive) and to indicate ‘neutral’ when they saw an
oval. Faces and ovals each were presented for 2 s
separated by a fixation cross (jittered, mean of 4 s). Data
were collected from two runs (approximately 337 TRs
and 11 m each).
Functional scans were acquired on a 1.5T GE Signa
scanner using a T2⁎ in-/out-spiral pulse sequence
(TE=40 ms, flip angle=90; Glover and Law, 2001)
consisting of 24 4-mm interleaved slices (axial in-plane
resolution 3.75×3.75 mm, no gap) at a temporal
resolution of 2 s (1.00 TR). All preprocessing and
analyses were conducted using Analysis of Functional
Neural Images (AFNI; Cox, 1996). Time series data
were concatenated, slice time and motion corrected,
excluding subjects who moved more than 1 mm. Data
were spatially smoothed with a 4-mm Gaussian kernel,
high-pass filtered, converted to percent signal change
and coregistered to anatomical images.
Preprocessed time series data for each individual
were analyzed with multiple regression. The neutral face
vs. oval contrast was convolved with a canonical hemo-
dynamic gamma-variate function response (Cohen,
1997), including terms for residual motion, trend, and
the neutral face vs. oval contrast regressors. Resulting
individual t-statistic maps were transformed into z-
scores and warped into Talaraich space (Talairach and
Tournoux, 1988). The CTL and SAD group maps were
analyzed with a two-sample t-test to compare neutral
face vs. oval contrast activations, and the t-scores were
then converted into z-scores.
For the a priori regions of interest (ROIs; left and
right amygdala), we used a Monte Carlo simulation
(1000 iterations) to determine a joint voxel-wise and
cluster size threshold protected at P<0.05, corrected.
Percent signal change to the neutral faces vs. oval
contrast was extracted from 2-mm radius spherical
masks at the peak voxel between groups in the bilateral
amygdala ROIs and was correlated with STAI scores.
3. Results
The CTL participants correctly identified a nonsignif-
icantly higher proportion of neutral faces than did the
56 R.E. Cooney et al. / Psychiatry Research: Neuroimaging 148 (2006) 55–59

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SAD participants (CTL: 90.95%; SAD: 84.37%), who
were nonsignificantly more likely than controls to
misidentify neutral faces as negative (CTL: 5.7%; SAD:
9.6%). Analyses of activations in the bilateral amygdala
ROIs for the neutral face vs. oval contrasts revealed that
whereas SAD participants demonstrated significantly
greater activation in the right amygdala [Tal., 19, −7,
−19] than controls (z=2.80, P=0.005; Fig. 1 — left),
CTLparticipantsexhibitedsignificantlygreateractivation
in the left amygdala [Tal., −19, −3, −17] than SAD
participants (z=−2.98, P=0.003; Fig. 1 — right). Impor-
tantly, the SAD and CTL groups did not differ signi-
ficantly in the time course to ovals, suggesting that the
group differences in amygdala activations in the neutral
face vs. ovals contrasts were not driven by increased
activation to ovals in the SAD group.
To assess whether this pattern of differential neural
responding to neutral faces extends to positive faces, we
alsoexaminedthehappyfacesvs.ovalcontrastintheSAD
and CTL groups. There was no group difference in either
the left amygdala (z=1.22, P=0.222) or the right
amygdala (z=0.564, P=0.573) for this contrast. Finally,
therewasalsonogroupdifferenceforthecontrastofhappy
vs. neutral faces in either the left amygdala (z=0.148,
P=0.882) or the right amygdala (z=0.125, P=0.901),
indicatingthatthegroupdifferenceinamygdalaactivation
is a function of how SAD and CTL participants differen-
tially activated to the neutral faces.
As expected, the SAD and CTL groups differed
significantly in levels of both state and trait anxiety
(STAI-S: SAD m=28.0, CTL m=45.0, t(18)=3.84;
STAI-T: SAD m=27.2, CTL m=54.2, t(18)=6.50,
both P's<0.001). Within the SAD group, mean percent
signal change in the right amygdala for the neutral face
vs. oval contrast was correlated significantly with scores
on both the STAI-S (r=0.69, P<0.03) and the STAI-T
(r=0.74, P<0.02); neither STAI-S nor STAI-T scores
were correlated with mean percent signal change in the
left amygdala (STAI-S: r=−0.46, P=0.19; STAI-T: r=
−0.18, P=0.62). In contrast, within the CTL group,
neither right nor left amygdala mean percent signal
change was correlated significantly with either STAI-S
or STAI-T scores (all P's>0.05). Finally, to examine
whether medication status was associated with activa-
tions within the SAD group, we compared activation to
neutral faces vs. ovals in the medicated (n=5) and the
unmedicated (n=5) SAD participants. There were no
significant differences between medicated and unmed-
icated SAD participants in activation in either the left or
right amygdala (left amygdala: z=0.067, P=0.50; right
amygdala: z=1.44, P=0.15).
4. Discussion
This is the first study to examine specifically neural
correlates of the processing of neutral faces in individuals
diagnosed with SAD. Previous studies investigating the
neural bases of SAD have shown amygdala and associated
limbic hyperactivity in response to threat-related facial
expressions. These studies, however, have used “neutral”
Fig. 1. (Left) Yellow activation in the right amygdala represents Social Anxiety Disorder (SAD)>Control (CTL). Bar graph depicts significant group
differences in mean percent signal change for the neutral faces vs. ovals contrast in the right amygdala for SAD and CTL groups (P=0.005). (Right)
Results of between-groups t-test for neutral faces vs. ovals. Blue activation in the left amygdala represents CTL>SAD. Bar graph depicts significant
group differences in meanpercent signalchange for the neutral faces vs. ovals contrast in the left amygdalafor CTL andSAD groups (P=0.003).(For
interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
57 R.E. Cooney et al. / Psychiatry Research: Neuroimaging 148 (2006) 55–59

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expressions as a baseline in contrast analyses (e.g.,Straube
et al., 2004; Amir et al., 2005). In the present study we
employed an event-related design to clarify and elucidate
thepatternofamygdalaactivationinresponsetofaceswith
neutral expressions in SAD and CTL participants. The
present results suggest not only that neutral faces actually
elicitaffectiveappraisalsinSADandCTLparticipants,but
more importantly, that they do so differentially. Whereas
SADindividualsexhibitedrightamygdalaactivationinthe
contrast of neutral faces vs. ovals, CTL participants
exhibited left amygdala activation. These findings have
importantimplicationsforinterpretingtheresultsofstudies
that have examined neural responses to negative faces in
individuals diagnosed with mood and anxiety disorders by
using neural activations to neutral faces as a contrast con-
dition (e.g., Thomas et al., 2001; Cannistraro et al., 2004).
Indeed, these results could explain discrepancies in the
findings obtained both within and across these studies.
Specifically,itisnotcleartowhatdegreepreviousfindings
of differential amygdala activation in SAD compared with
control participants are actually due to differential proces-
singofthenegativeemotionalexpressionsortodifferential
processing of the neutral faces that are commonly used as
the baseline or contrast condition.
Interestingly, the differential activation of the right
amygdala in SAD individuals and of the left amygdala in
CTL participants in response to neutral faces parallels
findings obtained in studies investigating the laterality of
the neural response to emotionally salient stimuli. The fact
that neutral faces elicited emotional processing in both
groups of participants indicates that neutral faces are best
conceptualized as emotionally ambiguous stimuli instead
of as neutral stimuli. These findings suggest that control
andSADparticipantsprocesstheseemotionallyambiguous
faces differently. Indeed, in studies of healthy participants,
left amygdala activation has been observed more consis-
tentlythanrightamygdalaactivationduringtasksinvolving
the processing of affective stimuli (Baas et al., 2004).
Combined with the present results in the CTL participants,
this pattern of findings offers further support for the
formulationthatneutralfacesareperceivedashavingsome
level of affect. Previous findings that left amygdala
activation is implicated in more sustained cognitive
appraisals of emotional stimuli, whereas right amygdala
activation is implicated in rapid orienting responses or
whenstimuliareambiguous(GlascherandAdolphs,2003;
Wright and Liu, 2006) suggest that SAD individuals are
quickly attending to, and evaluating, the neutral faces to a
greater degree than are the CTL participants.
Importantly, the elevated right-sided amygdala acti-
vation found in the SAD sample in response to neutral
facial expressions replicates findings of studies that have
investigated the processing of threatening stimuli in
anxiety disorders, specifically socialanxiety(Fredrikson
and Furmark, 2003; Straube et al., 2004; Phan et al.,
2006). Similarly, in a recent study of healthy controls,
Somerville et al. (2004) found that self-reported state
anxiety correlated positively with right amygdala activa-
tion to neutral faces. Consistent with these results, in the
present study we found a significant correlation between
right amygdala activation in response to the neutral faces
and levels of both state and trait anxiety within the SAD
group,furtherhighlightingapossiblelinkbetweenanxiety
and right-lateralized amygdala functioning.
It is important to point out that the relatively small
sample size in our study and the possibility of signal drop-
out in regions near the sinuses (e.g., the amygdala) may
limitthereliabilityofourfindings.Weshouldalsonotethat
thelateralityeffectintheprocessingofemotionalstimuliin
anxiety disorders is not a consistent finding; indeed, there
are reports of increased left amygdala activation in anxiety
disorders(e.g.,SAD:Steinetal.,2002;PTSD:Bryantetal.,
2005). Clearly, therefore, further research is required to
corroboratethepresenceofaright-lateralizedassociationin
individuals diagnosed with anxiety disorders during
emotional face processing. Equally important, the present
findings strongly indicate that future studies must include
baseline conditions other than neutral faces to elucidate
more systematically abnormal patterns of neural response
to emotional stimuli.
In closing, the present findings of right amygdala
activation to neutral faces in participants diagnosed with
SAD, but not in controls, suggest a hyperactivity in the
threat-detection and emotional evaluation system of SAD
individuals when they are confronted with ambiguous
interpersonal stimuli. These results clearly underscore the
importance of selecting adequate baseline or control
conditions in studies investigating neural correlates of the
processing of emotional stimuli in individuals experienc-
ing emotional disorders.
Acknowledgments
We thank Anne Sawyer-Glover, Jenni Champion,
Kathryn Dingman, and Faith Brozovich for their assis-
tance. This research was supported by NIMH Grant
MH59259 to Ian H. Gotlib.
References
Amir, N., Elias, J., Klumpp, H., Przeworski, A., 2003. Attentional bias
to threat in social phobia: facilitated processing of threat or
difficulty disengaging attention from threat? Behavioral Research
and Therapy 41, 1325–1335.
58 R.E. Cooney et al. / Psychiatry Research: Neuroimaging 148 (2006) 55–59

Page 5

Amir, N., Klumpp, H., Elias, J., Bedwell, J.S., Yanasak, N., Miller, L.S.,
2005. Increased activation of the anterior cingulate cortex during
processing of disgust faces in individuals with social phobia.
Biological Psychiatry 57, 975–981.
Baas, D., Aleman, A., Kahn, R.S., 2004. Lateralization of amygdala
activation: a systematic review of functional neuroimaging studies.
Brain Research Brain Research Reviews 45, 96–103.
Birbaumer, N., Grodd, W., Diedrich, O., Klose, U., Erb, M., Lotze, M.,
Schneider, F., Weiss, U., Flor, H., 1998. fMRI reveals amygdala
activationtohumanfacesinsocialphobics.Neuroreport9,1223–1226.
Bryant, R.A., Felmingham, K.L., Kemp, A.H., Barton, M., Peduto, A.S.,
Rennie, C., Gordon, E., Williams, L.M., 2005. Neural networks of
information processing in posttraumatic stress disorder: a functional
magneticresonanceimagingstudy.BiologicalPsychiatry58,111–118.
Cannistraro, P.A., Wright, C.I., Wedig, M.M., Martis, B., Shin, L.M.,
Wilhelm, S., Rauch, S.L., 2004. Amygdala responses to human faces
inobsessive–compulsivedisorder.BiologicalPsychiatry56,916–920.
Clark, D.M., McManus, F., 2002. Information processing in social
phobia. Biological Psychiatry 51, 92–100.
Cohen, M.S., 1997. Parametric analysis of fMRI data using linear
systems methods. Neuroimage 6, 93–103.
Cox, R.W., 1996. AFNI: software for analysis and visualization of
functional magnetic resonance neuroimages. Computers and
Biomedical Research 29, 162–173.
Cramer, V., Torgersen, S., Kringlen, E., 2005. Quality of life and
anxiety disorders: a population study. Journal of Nervous and
Mental Disease 193, 196–202.
First,M.B.,Spitzer,R.L.,Gibbon,M., Williams, J.B.,1996.Structured
Clinical Interview for DSM-IV. American Psychiatric Association,
Washington, DC.
Fredrikson, M., Furmark, T., 2003. Amygdaloid regional cerebral
blood flow and subjective fear during symptom provocation in
anxiety disorders. Annals of the New York Academy of Sciences
985, 341–347.
Glascher, J., Adolphs, R., 2003. Processing of the arousal of subli-
minal and supraliminal emotional stimuli by the human amygdala.
Journal of Neuroscience 23, 10274–10282.
Glover, G.H., Law, C.S., 2001. Spiral-in/out BOLD fMRI for
increased SNR and reduced susceptibility artifacts. Magnetic
Resonance in Medicine 46, 515–522.
Lundh, L.G., Ost, L.G., 1996. Recognition bias for critical faces in
social phobics. Behaviour Research and Therapy 34, 787–794.
Phan, K.L., Fitzgerald, D.A., Nathan, P.J., Tancer, M.E., 2006.
Association between amygdala hyperactivity to harsh faces and
severity of social anxiety in generalized social phobia. Biological
Psychiatry 59, 424–429.
Schneider, F., Weiss, U., Kessler, C., Müller-Gartner, H.W., Posse, S.,
Salloum, J.B., Grodd, W., Himmelmann, F., Gaebel, W., Birbaumer,
N.,1999.Subcorticalcorrelates of differential classicalconditioningof
aversiveemotionalreactionsinsocialphobia.BiologicalPsychiatry45,
863–871.
Somerville, L.H., Kim, H., Johnstone, T., Alexander, A.L., Whalen, P.J.,
2004. Human amygdala responses during presentation of happy and
neutral faces: correlations with state anxiety. Biological Psychiatry
55, 897–903.
Spielberger,C.,Gorsuch,R.,Lushene,R.,1970.ManualfortheState-Trait
Anxiety Inventory. Consulting Psychologists Press, Palo Alto, CA.
Stein,M.B.,Goldin,P.R.,Sareen,J.,Zorrilla,L.T., Brown,G.G.,2002.
Increased amygdala activation to angry and contemptuous faces in
generalized social phobia. Archives of General Psychiatry 59,
1027–1034.
Straube, T., Kolassa, I.T., Glauer, M., Mentzel, H.J., Miltner, W.H.,
2004. Effect of task conditions on brain responses to threatening
faces in social phobics: an event-related functional magnetic reso-
nance imaging study. Biological Psychiatry 56, 921–930.
Talairach, J., Tournoux, P., 1988. Co-Planar Stereotaxic Atlas of the
Human Brain, 3-Dimensional Proportional System: An Approach
to Cerebral Imaging. Thieme Medical Publisher, Inc., Georg
Thieme Verlag, New York.
Thomas, K.M., Drevets, W.C., Dahl, R.E., Ryan, N.D., Birmaher, B.,
Eccard, C.H., Axelson, D., Whalen, P.J., Casey, B.J., 2001. Amy-
gdala response to fearful faces in anxious and depressed children.
Archives of General Psychiatry 58, 1057–1063.
Veit, R., Flor, H., Erb, M., Hermann, C., Lotze, M., Grodd, W.,
Birbaumer, N., 2002. Brain circuits involved in emotional learning
in antisocial behavior and social phobia in humans. Neuroscience
Letters 328, 233–236.
Winton, E.C., Clark, D.M., Edelmann, R.J., 1995. Social anxiety, fear
of negative evaluation and the detection of negative emotion in
others. Behaviour Research and Therapy 33, 193–196.
Wright, P., Liu, Y., 2006. Neutral faces activate the amygdala during
identity matching. Neuroimage 29, 628–636.
59 R.E. Cooney et al. / Psychiatry Research: Neuroimaging 148 (2006) 55–59