How we know it hurts: item analysis of written narratives reveals distinct neural responses to others' physical pain and emotional suffering

Abstract

People are often called upon to witness, and to empathize with, the pain and suffering of others. In the current study, we directly compared neural responses to others' physical pain and emotional suffering by presenting participants (n = 41) with 96 verbal stories, each describing a protagonist's physical and/or emotional experience, ranging from neutral to extremely negative. A separate group of participants rated "how much physical pain", and "how much emotional suffering" the protagonist experienced in each story, as well as how "vivid and movie-like" the story was. Although ratings of Pain, Suffering and Vividness were positively correlated with each other across stories, item-analyses revealed that each scale was correlated with activity in distinct brain regions. Even within regions of the "Shared Pain network" identified using a separate data set, responses to others' physical pain and emotional suffering were distinct. More broadly, item analyses with continuous predictors provided a high-powered method for identifying brain regions associated with specific aspects of complex stimuli - like verbal descriptions of physical and emotional events.

Figure 1. Item-wise correlations of brain activity with ratings of physical pain and emotional suffering.

Regression analyses identified the brain regions where brain activity was most highly correlated with behavioral ratings of (A) “How much physical pain was the main character in?” (hot), and (B) “How much emotional suffering did the main character experience?” (cool). The brain regions where activity correlated with ratings of physical pain (A) include the bilateral insula cortex (Ins), anterior middle cingulate cortex (AMCC), bilateral middle frontal gyrus (MFG), bilateral secondary sensory regions (SII) and right extrastriate body area (EBA). The brain regions where activity correlated with ratings of emotional pain (suffering) (B) included the left dorsal striatum/anterior thalamus (Thal), precuneus (PC), posterior cingulate cortex (PCC), and regions in the medial prefrontal cortex (MPFC). Shown in (C) are both the regions where activity correlated with Pain (red), where activity correlated with Suffering (blue), and the conjunction of the two (white). All analyses are shown at p<0.05, corrected.

Figure 2. Ratings of Pain, Suffering and Vividness compared to brain activity in 8 ROIs.

The average ratings of Physical Pain and Emotional Suffering experienced by the protagonist in each story, and the overall Vividness of the scene were compared to brain activity elicited for each story in 8 ROIs identified in a separate data set. Shown in (A) are the 5 ROIs that loaded negatively onto the first factor of the principal component analysis, and in (B) the 3 ROIs that loaded positively onto that first factor. Pain, Suffering and Vividness were rated on a scale from 1 (none) to 9 (extreme), and brain activity was measured as the average beta value within each ROI. ** p<0.002 (significant, correcting for multiple comparisons). SII  =  secondary sensory cortex, Ins  =  insula, AMCC  =  anterior middle cingulate cortex, Thal  =  anterior thalamus, DMPFC  =  dorsomedial prefrontal cortex.