Motor Activity During the Observation of Dynamic Emotional Facial Expressions Is Intact in Autism Spectrum Disorder

Background: According to the mirror neuron theory of autism spectrum disorder (ASD), ASD is characterized by reduced activity in neural systems that mirror observed actions, sensations and emotions in typically developing individuals (TDs). Observation of facial emotional expressions involves two types of mirroring: 1) activation of motor areas involved in producing facial expressions and 2) activation of areas involved in experiencing the same emotion.

Objectives: With this fMRI study we tested whether adults with ASD activate their motor system as much as TDs while viewing movies of facial expressions.

Methods: We scanned 17 high functioning adults with ASD and 17 age and IQ matched TDs while they passively viewed movies of pleased, disgusted and neutral facial expressions and while they performed a simple motor task (pulling up the nose).

Results:  The motor task showed no significant differences between groups (p>.001), so we created a single motor mask (facial movement – baseline) combining all participants. Several areas within this mask were active for ASD adults during facial expression observation relative to baseline, including right insula, BA44, MI, premotor/supplementary motor cortex and right STS. Importantly, there were no significant differences in these areas between groups (p>.005). Lowering the threshold revealed stronger activations for ASD in a between-group comparison. Disregarding the mask, ASD adults demonstrated stronger activations in amongst others emotional and mentalizing areas, particularly while viewing disgusted expressions (p<.005).

Conclusions: We found that adults with ASD activate their motor system at least as strongly as TDs when observing dynamic facial expressions. This result challenges the mirror neuron theory of autism. Hyperactivation of emotional and mentalizing areas suggests people with ASD may react excessively to emotional facial expressions, and therefore turn away from other people’s faces. Alternatively, they may compensate less efficient processing by recruiting more neural resources or might be more motivated.