Broken or socially mistuned mirroring in ASD? An investigation via transcranial magnetic stimulation.

Individuals with an autism spectrum disorder (ASD) experience persistent difficulties during social interactions and communication. Previously, it has been suggested that deficits in the so-called "mirror system," active during both action execution and observation, may underlie these social difficulties. It is still a topic of debate however whether deficiencies in the simulation of others' actions (i.e., "broken" mirroring) forms a general feature of ASD, or whether these mostly reflect a lack of social attunement. The latter would suggest an overall intact mirror system, but an impaired modulation of mirror activity according to variable social contexts. In this study, 25 adults with ASD and 28 age- and IQ-matched control participants underwent transcranial magnetic stimulation during the observation of hand movements under variable conditions. Hand movements were presented via a live interaction partner, either without social context to assess basic motor mirroring or in combination with direct and averted gaze from the actor to assess socially modulated mirroring. Overall, no significant group differences were revealed, indicating no generally diminished mirror activity in ASD. Interestingly however, regression analyses revealed that, among ASD participants, higher symptom severity was associated with both reduced basic motor mirroring and aberrant socially modulated mirroring (i.e., no enhancement of mirror system activity upon observation of the interaction partner's direct vs. averted gaze). These findings further challenge the notion that mirror system dysfunctions constitute a principal feature of ASD, but demonstrate that variations in mirroring may be related to differential expressions of ASD symptom severity. LAY SUMMARY: Our findings show similar activity levels in brain regions responsible for action simulation and understanding in adults with autism, compared to adults without autism. However, the presence of more severe autism symptoms was linked to reduced activity in these regions. This suggests lower levels of brain activity during action understanding in some, but not all, persons with autism, which may contribute to the social difficulties these persons experience in daily life.