Intracranial human recordings reveal association between neural activity and perceived intensity for the pain of others in the insula

Based on neuroimaging data, the insula is considered important for people to empathize with the pain of others. Here we present intracranial electroencephalographic (iEEG) recordings and single-cell recordings from the human insulae while 7 epilepsy patients rated the intensity of a woman's painful experiences seen in short movie clips. Pain had to be deduced from seeing facial expressions or a hand being slapped by a belt. We found activity in the broadband 20-190 Hz range correlated with the trial-by-trial perceived intensity in the insula for both types of stimuli. Within the insula, some locations had activity correlating with perceived intensity for our facial expressions but not for our hand stimuli, others only for our hand but not our face stimuli, and others for both. The timing of responses to the sight of the hand being hit is best explained by kinematic information; that for our facial expressions, by shape information. Comparing the broadband activity in the iEEG signal with spiking activity from a small number of neurons and an fMRI experiment with similar stimuli, revealed a consistent spatial organization, with stronger associations with intensity more anteriorly, while viewing the hand being slapped.