Segregated Limbic Cortical Pathways

The available evidence suggests that limbic-cortical pathways are sufficiently segregated among different emotional systems, with some overlap in regions such as medial prefrontal cortex, insula, and cerebellar vermis (Phan et al., 2002; Damasio et al., 2000; Liotti et al., 2000a), possibly subserving common dimensions of emotion (such as arousal). The task of identifying such segregated pathways is complicated by the frequent coexistence of different basic emotions in both normal feelings and affective disorders, and by the fact that only a few studies report cortical deactivations (critical to an evaluation of such networks).

In a comparison to transient memory-script-induced sadness and anxiety in healthy subjects (Liotti et al., 2000a), it was found that the regions involved in emotion generation and suppression (neocortex) are distinct for sadness versus anxiety, with dorsal cortical regions—right dorsolateral BA9 and inferior parietal cortex BA40—more involved in the control/expression of sadness, and ventral regions, particularly the inferior temporal cortex and parahippocampal gyri, more involved in the control/expression of anxiety (Fig. 2.9).

This hypothesized model fits with reports of (1) prefrontal and inferior parietal abnormalities in clinical depression, but not with inferior temporal and parahippocam-pal ones (Bench et al., 1992; Mayberg, 1997); (2) prominent inferior and middle temporal but not inferior parietal deactivations in anxiety patients with PTSD (i.e., Bremner et al., 1999); and most strikingly, (3) consistent findings of right parahippocampal

Sadness

Anxiety

Figure 2.9. Segregated limbic-cortical pathways in sadness and anxiety. In sadness (left), cortical deactivations (thick blue and thick arrows) are chiefly dorsal, in right dorsolateral prefrontal BA9 (RDPF9) and inferior parietal BA40 (iPar40). Activations (thick red) are in ventral (subgenual) cingulate BA25 (vCg25), and dorsal insula (dIns). In anxiety, cortical deactivations (thick blue and thick arrows) are chiefly ventral, in inferior temporal gyrus BA37 (iTemp37) and parahippocampal gyrus BA36 (GH36), and activations (thick red) are in orbitofrontal cortex, anterior temporal poles (OF-aT), and ventral insula (vIns). Dashed lines indicate regions not showing significant signal change. Other abbreviations: Amygdala (Amg), posterior cingulate BA31 (pCg31). [These data are adapted from Liotti et al. (2000a).] See ftp site for color image.

Sadness

Anxiety

Figure 2.9. Segregated limbic-cortical pathways in sadness and anxiety. In sadness (left), cortical deactivations (thick blue and thick arrows) are chiefly dorsal, in right dorsolateral prefrontal BA9 (RDPF9) and inferior parietal BA40 (iPar40). Activations (thick red) are in ventral (subgenual) cingulate BA25 (vCg25), and dorsal insula (dIns). In anxiety, cortical deactivations (thick blue and thick arrows) are chiefly ventral, in inferior temporal gyrus BA37 (iTemp37) and parahippocampal gyrus BA36 (GH36), and activations (thick red) are in orbitofrontal cortex, anterior temporal poles (OF-aT), and ventral insula (vIns). Dashed lines indicate regions not showing significant signal change. Other abbreviations: Amygdala (Amg), posterior cingulate BA31 (pCg31). [These data are adapted from Liotti et al. (2000a).] See ftp site for color image.

deactivation associated with normal and pathologic panic attacks and anxiety provocation, highly suggestive of a role of this structure in the suppression of efferent emotional responses (Reiman, 1997; Reiman et al., 1989). The observation of greater dorsal cortical deactivations (right prefrontal BA9, posterior parietal BA40/7) during sadness as compared to anxiety, and greater ventral cortical deactivations (inferior temporal BA37/20, parahippocampal gyri BA35/36) during anxiety as compared to sadness, also fit with a previous theoretical model. Liotti and Tucker (1995) proposed that asymmetries in dorsal/ventral cortical streams are relevant not only to differences in cognitive processing but also to differences in motivational/emotional control, with the dorsal stream more involved in the regulation of emotional phasic arousal (from sadness/depression to happiness/mania) and the ventral stream more involved in the regulation of emotional tonic activation (from relaxation to anxiety and hostility; Liotti and Tucker, 1995).

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