Disrupted amygdalar subregion functional connectivity and evidence of a compensatory network in generalized anxiety disorder

Abstract

Context: Little is known about the neural abnormalities underlying generalized anxiety disorder (GAD). Studies in other anxiety disorders have implicated the amygdala, but work in GAD has yielded conflicting results. The amygdala is composed of distinct subregions that interact with dissociable brain networks, which have been studied only in experimental animals. A functional connectivity approach at the subregional level may therefore yield novel insights into GAD.

Objectives: To determine whether distinct connectivity patterns can be reliably identified for the basolateral (BLA) and centromedial (CMA) subregions of the human amygdala, and to examine subregional connectivity patterns and potential compensatory amygdalar connectivity in GAD.

Design: Cross-sectional study.

Setting: Academic medical center.

Participants: Two cohorts of healthy control subjects (consisting of 17 and 31 subjects) and 16 patients with GAD.

Main outcome measures: Functional connectivity with cytoarchitectonically determined BLA and CMA regions of interest, measured during functional magnetic resonance imaging performed while subjects were resting quietly in the scanner. Amygdalar gray matter volume was also investigated with voxel-based morphometry.

Results: Reproducible subregional differences in large-scale connectivity were identified in both cohorts of healthy controls. The BLA was differentially connected with primary and higher-order sensory and medial prefrontal cortices. The CMA was connected with the midbrain, thalamus, and cerebellum. In GAD patients, BLA and CMA connectivity patterns were significantly less distinct, and increased gray matter volume was noted primarily in the CMA. Across the subregions, GAD patients had increased connectivity with a previously characterized frontoparietal executive control network and decreased connectivity with an insula- and cingulate-based salience network.

Conclusions: Our findings provide new insights into the functional neuroanatomy of the human amygdala and converge with connectivity studies in experimental animals. In GAD, we find evidence of an intra-amygdalar abnormality and engagement of a compensatory frontoparietal executive control network, consistent with cognitive theories of GAD.

Figure 1.

Differential connectivity of the basolateral (BLA) and centromedial (CMA) amygdalar subregions during resting-state functional magnetic resonance imaging. Findings are shown in 2 separate cohorts of healthy subjects (A and B) and a formal conjunction between these cohorts (C). The BLA connectivity was primarily cortical, whereas the CMA connectivity was primarily subcortical. Color scales represent t scores for the main effect of region in a voxelwise analysis of variance. Red indicates that BLA connectivity is increased compared with CMA connectivity; blue, CMA connectivity is increased compared with BLA connectivity. FG indicates fusiform gyrus; M1/S1, primary somatosensory and motor cortices; Occ, occipital cortex; OFC, orbitofrontal cortex; PAG, periaqueductal gray; STG, superior temporal gyrus; vmPFC, ventromedial prefrontal cortex; and VTA/SN, ventral tegmental area/substantia nigra.

Figure 2.

Specificity of amygdalar subregion connectivity with target regions in healthy subjects and patients with generalized anxiety disorder (GAD). A, Connectivity of the basolateral (BLA) or the centromedial (CMA) amygdalar regions of interest (ROIs), separately on the right and left sides, with target networks defined by differential BLA vs CMA connectivity maps from the analysis of variance (ANOVA) effect of region analysis from just the first control cohort (GAD controls) (shown in Figure 1A). Dissociable patterns of BLA and CMA connectivity (eg, greater connectivity of BLA ROIs with BLA targets than with CMA targets, and the reverse for CMA ROIs) were found to a similar degree in both control cohorts but were significantly reduced in GAD patients, who were demographically matched with the GAD controls. Bars represent mean values; error bars, standard error of the mean. B, Results of a voxelwise group×region ANOVA comparing differential BLA-CMA connectivity in healthy controls and GAD patients. Significance in this analysis would mean that there is a group difference in the dissociability of BLA-CMA connectivity because of decreased connectivity with the correct targets or because of increased connectivity with the incorrect targets in 1 group. That BLA and CMA targets (see labels) are significant suggests that there is an intra-amygdalar subregional disorganization in the GAD patients rather than alterations in the connectivity of the amygdala with some targets but not others. Results are displayed at P=.05, uncorrected, to ensure a complete view of group differences. The color scales reflect F scores from the ANOVA. C, A voxel-based morphometry analysis of structural magnetic resonance images from the GAD controls and GAD patients, focusing on the amygdalar subregions used for the functional connectivity analyses, identified increased gray matter volume in the right CMA subregion in GAD patients. *P=.03. Bars represent mean values; error bars, standard error of the mean. AU indicates arbitrary units.

Figure 3.

Group connectivity differences across amygdalar subregions and evidence of a compensatory network in generalized anxiety disorder (GAD). A, The analysis of variance (ANOVA) effect of group is shown for the basolateral amygdalar subregions (BLA). B, The ANOVA effect of group is shown for the centromedial amygdalar subregions (CMA). Red indicates connectivity was increased in GAD patients compared with control cohorts; blue, connectivity was increased in control cohorts compared with GAD patients. Thus, the majority of blue in part A indicates decreased connectivity of GAD patients’ BLA to normal BLA targets, whereas the majority of red in part B indicates increased inappropriate connectivity of GAD patients’ CMA to normal BLA targets. C, Common increased or decreased connectivity in GAD patients across both amygdalar subregions identifies a bilateral frontoparietal network with increased connectivity (red) and a bilateral insulocingulate network with decreased connectivity (blue). For figure clarity, only the right side of the brain is shown. D, Subregional connectivity of the right dorsolateral prefrontal cortex (DLPFC) from part C in controls and GAD patients demonstrates that this is an adaptation in patients not normally seen in controls. Bars represent mean values; error bars, standard error of the mean. E, Average connectivity of the right DLPFC to the amygdala in GAD patients is negatively correlated with anxiety scores, suggesting that it reflects connectivity with a compensatory network.