Abstract
Threatening faces are potent cues in social anxiety disorder (SAD); therefore, neural response to threatening faces, particularly regions in the “fear” circuit such as amygdala, may classify individuals with SAD. Previous studies of indirect/implicit processing of threatening faces have shown that support vector machine (SVM) pattern recognition significantly differentiates individuals with SAD from healthy participants, though evidence for the role of the fear circuit in classification has been inconsistent. We extend this literature by using SVM during direct face processing. Individuals with SAD (n=47) and healthy controls (n=46) completed a validated emotional face matching task during functional MRI, which included a matching shapes control condition. SVM was based on brain response to threat (vs. happy) faces, threat faces (vs. shapes), and threat/happy faces (vs. shapes) in 90 regions encompassing frontal, limbic, parietal, temporal, and occipital systems. Recursive feature elimination (RFE) was used for feature selection and to rank the contribution of regions in predicting SAD diagnosis. SVM results for threat (vs. happy) faces revealed satisfactory accuracy (e.g., area under the curve=0.72); results with shapes as “baseline” yielded less optimal classification. RFE for threat (vs. happy) indicated that all 90 brain regions were necessary for classification. RFE-based ranking suggested diffuse neurofunctional activation to threat (vs. happy) faces in classification. When using an RFE cut-point, regions implicated in sensory and goal-directed processes contributed relatively more in differentiating SAD from controls than other regions. Results suggest that neural activity across large-scale systems, as opposed to fear circuitry alone, may aid in the diagnosis of SAD.
Highlights
Social anxiety disorder (SAD) is one of the most common anxiety disorders in the United States [1] and a major public health problem
Results showed that the social anxiety disorder (SAD) group was more socially anxious [Liebowitz Social Anxiety Scale (LSAS); t(91) = 24.01, p < 0.001], generally anxious [Hamilton Anxiety Rating Scale (HAM-A); t(91) = 11.21, p
Recursive feature elimination (RFE) feature importance (i.e., Fischer score) results yielded a smooth decay across regions of interest (ROIs) as opposed to a robust inflection separating high and low feature importance (Figure 2)
Summary
Social anxiety disorder (SAD) is one of the most common anxiety disorders in the United States [1] and a major public health problem. It is characterized by excessive fear and avoidance in a range of situations that involve potential negative judgment by others [2] and is associated with severe impairment [3,4,5]. In light of social fears, this work has generally used threatening facial expressions and focused on brain regions central to threat processing and the mediation of fear responses (e.g., amygdala, insula, infralimbic cortex) [8,9,10]. Neuroimaging results based on group effects (e.g., SAD vs. controls) do not delineate which regions predict SAD status at the individual level, the objective of brain-based markers of SAD
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