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Open Access Research article

Spider phobia is associated with decreased left amygdala volume: a cross-sectional study

Melanie S Fisler1*, Andrea Federspiel1, Helge Horn1, Thomas Dierks1, Wolfgang Schmitt1, Roland Wiest2, Dominique J-F de Quervain3 and Leila M Soravia1

Author Affiliations

1 Department of Psychiatric Neurophysiology, University Hospital of Psychiatry, University of Bern, Bolligenstrasse 111 3000, Bern, 60, Switzerland

2 Diagnostic and Interventional Neuroradiology, Inselspital and University of Bern, OP-Ost C215, Bern, 3010, Switzerland

3 Division of Cognitive Neuroscience, Faculty of Medicine & Faculty of Psychology, University of Basel, Birmannsgasse 8 4055, Basel, Switzerland

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BMC Psychiatry 2013, 13:70  doi:10.1186/1471-244X-13-70

Published: 26 February 2013

Abstract

Background

Evidence from animal and human studies imply the amygdala as the most critical structure involved in processing of fear-relevant stimuli. In phobias, the amygdala seems to play a crucial role in the pathogenesis and maintenance of the disorder. However, the neuropathology of specific phobias remains poorly understood. In the present study, we investigated whether patients with spider phobia show altered amygdala volumes as compared to healthy control subjects.

Methods

Twenty female patients with spider phobia and twenty age-matched healthy female controls underwent magnetic resonance imaging to investigate amygdala volumes. The amygdalae were segmented using an automatic, model-based segmentation tool (FSL FIRST). Differences in amygdala volume were investigated by multivariate analysis of covariance with group as between-subject factor and left and right amygdala as dependent factors. The relation between amygdala volume and clinical features such as symptom severity, disgust sensitivity, trait anxiety and duration of illness was investigated by Spearman correlation analysis.

Results

Spider phobic patients showed significantly smaller left amygdala volume than healthy controls. No significant difference in right amygdala volume was detected. Furthermore, the diminished amygdala size in patients was related to higher symptom severity, but not to higher disgust sensitivity or trait anxiety and was independent of age.

Conclusions

In summary, the results reveal a relation between higher symptom severity and smaller left amygdala volume in patients with spider phobia. This relation was independent of other potential confounders such as the disgust sensitivity or trait anxiety. The findings suggest that greater spider phobic fear is associated with smaller left amygdala. However, the smaller left amygdala volume may either stand for a higher vulnerability to develop a phobic disorder or emerge as a consequence of the disorder.

Keywords:
Spider phobia; Amygdala; Morphology