Neural Mechanisms of Empathy for Physical and Social Pain and Their Relation to Autistic Traits

Background: Empathy is a core social ability affected in ASD and the broader autism phenotype. Empathic response relies on brain circuitry common to both the experience of pain and its observation in another. Event-related potential (ERP) studies reveal distinct stages of empathic processing of observed physical pain: an automatic, rapid (~140-80 ms) response and a subsequent, longer-latency component (~380 ms) that is modulated by attention and presumed to reflect cognitive appraisal. Recent neuroimaging research suggests that observation of social distress activates mentalizing circuitry, as well as social-pain related regions, including the insula and anterior cingulate cortex. The temporal dynamics of empathy for social pain remain unexplored.

Objectives: This study aimed to (a) describe the time course of empathic processing of social pain, (b) contrast it with response to observed physical pain, and (c) explore the relationship among these indices of social sensitivity and subthreshold autistic symptomatology. We predicted that oscillatory EEG would demonstrate activation common to both social and physical empathic processing; however, given more extensive cognitive appraisal required for detection of social distress, we predicted ERPs would reveal a slower time course for social empathic response. Autistic traits were hypothesized to correlate with attenuated empathic response. 

Methods: Participants included 30 typical adults pre-screened for high versus low levels of autistic traits (Autism-Spectrum Quotient). EEG was recorded with a 128-electrode Hydrocel Geodesic Sensor net while participants viewed dynamic and static stimuli displaying hands in physically painful, socially painful, and matched painless contexts. Participants viewed stimuli under two conditions, performing an empathic task (rate distress) or a distractor task (count bracelets worn by actors). Mu power (8-13 Hz) was computed over central electrodes (video stimuli), and log ratios (empathic attention: distractor condition) were compared in social versus physical conditions. ERPs were extracted for each condition (static stimuli) at leads corresponding to those used in prior research on electrophysiological indices of empathy (F3/F4, C3/C4, T5/T6, P3/P4).

Results: Consistent with previous research, a short-latency ERP component differentiated painful and painless stimuli at frontal and central electrodes during observation of physical pain. Though social pain was not reflected in this early component, a subsequent component differentiated between painful and painless stimuli in both physical and social pain conditions but only in the pain evaluation task. Analysis of mu attenuation revealed comparable response to observing the physical and social pain of others; both conditions elicited greater mu attenuation than painless stimuli. Analyses in progress examine the correlation between ERP amplitude, mu power, and subclinical autistic symptoms. 

Conclusions: This is the first investigation of the temporal dynamics of empathy for social pain, revealing a slower time course that is distinct from that observed for physical pain. Mu attenuation, which is presumed to reflect activity in an action-perception system and has been correlated with empathy in other studies, revealed common activation for observation of both physical and social pain in others. Analyses in progress will clarify the role of empathic processing in the broader autism phenotype.