Infection, incest, and iniquity: investigating the neural correlates of disgust and morality

Abstract

Disgust, an emotion related to avoiding harmful substances, has been linked to moral judgments in many behavioral studies. However, the fact that participants report feelings of disgust when thinking about feces and a heinous crime does not necessarily indicate that the same mechanisms mediate these reactions. Humans might instead have separate neural and physiological systems guiding aversive behaviors and judgments across different domains. The present interdisciplinary study used functional magnetic resonance imaging (n = 50) and behavioral assessment to investigate the biological homology of pathogen-related and moral disgust. We provide evidence that pathogen-related and sociomoral acts entrain many common as well as unique brain networks. We also investigated whether morality itself is composed of distinct neural and behavioral subdomains. We provide evidence that, despite their tendency to elicit similar ratings of moral wrongness, incestuous and nonsexual immoral acts entrain dramatically separate, while still overlapping, brain networks. These results (i) provide support for the view that the biological response of disgust is intimately tied to immorality, (ii) demonstrate that there are at least three separate domains of disgust, and (iii) suggest strongly that morality, like disgust, is not a unified psychological or neurological phenomenon.

Figure 1

An illustration of the organization of the 12 blocks in each run: 3 neutral (N), 3 pathogen (P), 3 incest (I ), and 3 nonsexual moral (M).

Figure 2

Self-report ratings. M = nonsexual moral acts; I = incest acts; P = pathogen acts; N = neutral acts. ns = not significant.

Figure 3

Conjunction analysis of all disgust > neutral conditions (pathogen + incest + nonsexual moral > neutral) overlaid on SPM2 canonical T1 brain. (FDR corrected p < .001, cluster minimum = 10 voxels, neurological convention).

Figure 4

Regions more active in pathogen condition than in the sociomoral and neutral conditions (pathogen > sociomoral) overlaid on SPM2 canonical T1 image. (FDR corrected p < .05, cluster minimum = 10 voxels, neurological convention).

Figure 5

Regions more active in the sociomoral condition than in the pathogen and neutral conditions (sociomoral > pathogen) overlaid on SPM2 canonical T1 image. (FDR corrected p < .001, cluster minimum = 10 voxels, neurological convention).

Figure 6

Regions more active in the incest condition than in the nonsexual moral condition (incest > nonsexual moral) overlaid on SPM2 canonical T1 image. (FDR corrected p < .0001, cluster minimum = 10 voxels, neurological convention).