BACKGROUND: Asperger syndrome (AS) is a neurodevelopmental condition within the autism spectrum conditions (ASC) characterized by specific difficulties in communication, social interaction, and empathy that is essential for sharing and understanding others' feelings and emotions. Although reduced empathy is considered a core feature of ASC, neurophysiological evidence of empathic deficits before and below mentalizing and perspective taking is lacking. We explored whether people with AS differ from neurotypical control participants in their empathic corticospinal response to the observation of others' pain and the modulatory role played by phenomenal experience of observed pain and personality traits.
METHODS: Sixteen right-handed men with AS (aged 28.0+/-7.2 years) and 20 neurotypical controls (aged 25.3+/-6.7 years) age, sex, and IQ matched, underwent single-pulse transcranial magnetic stimulation during observation of painful and nonpainful stimuli affecting another individual.
RESULTS: When observing other's pain, participants with AS, in contrast to neurotypical control participants, did not show any amplitude reduction of motor-evoked potentials recorded from the muscle vicariously affected by pain, nor did their neurophysiological response correlate with imagined pain sensory qualities. Participants with AS represented others' pain in relation to the self-oriented arousal experienced while watching pain videos.
CONCLUSIONS: Finding no embodiment of others' pain provides neurophysiological evidence for reduced empathic resonance in people with AS and indicates that their empathic difficulties involve not only cognitive dimensions but also sensorimotor resonance with others. We suggest that absence of embodied empathy may be linked to changes at very basic levels of neural processing.