Understanding why people with autism and schizophrenia have difficulties with social interaction
Researchers from Aarhus University and the University of Copenhagen report new experimental evidence that the brain’s mirror system plays a causal role in how people understand the actions of others. The study, to be published in Psychological Science, shows that specific motor regions involved in producing actions also contribute directly to interpreting observed actions, a finding that sheds light on mechanisms relevant to social cognition in conditions such as autism and schizophrenia.
Using a noninvasive magnetic stimulation method, the research team temporarily disrupted normal processing in motor areas of healthy adult participants and then measured how this disruption affected the ability to understand observed actions. Unlike prior studies that relied mainly on correlations between brain activity and behavior, this experiment provides causal evidence: when motor regions were briefly impaired, participants’ ability to identify pantomimed actions declined. This direct manipulation strengthens the interpretation that the mirror system contributes to action understanding rather than merely reflecting it.
Understanding autism and schizophrenia
The findings are relevant to ongoing efforts to understand social difficulties experienced by some people with autism spectrum disorder and schizophrenia. Because the same brain regions appear to be involved both in producing actions and in interpreting the actions of others, impairment or atypical functioning of this mirror system could be one factor that interferes with spontaneous social understanding.
The authors caution that this result represents one piece of a much larger puzzle. Social cognition is complex and depends on many brain systems and developmental, genetic, and environmental factors. Still, clarifying the causal role of motor-related mirror regions provides a clearer target for future research, and may be useful for clinicians, therapists and educators who design interventions to support social interaction.
“There has been a great deal of interest in the mirror system,” says John Michael, one of the study’s authors. “Our experiment offers clear and straightforward evidence that these motor-related areas help people make sense of other people’s actions.”
Study participants and task
The experiment tested 20 adult volunteers who visited the lab on three occasions. On the first visit participants underwent brain scans to identify the motor areas of interest. On the second and third visits researchers applied magnetic stimulation to temporarily disrupt processing in those regions. After stimulation, participants completed a standard action-understanding task: they watched about 250 short videos of actors pantomiming everyday actions, and after each clip they selected the object that best matched the pantomime. For example, viewing a pantomime of hammering should prompt the participant to choose a hammer.
Performance on this task declined when the motor regions were stimulated, indicating that normal function in those areas contributes to accurately interpreting observed actions. The stimulation method used causes only temporary disruption that wears off after approximately 20 minutes, making it a safe tool for causal investigation.
Innovative stimulation method
The researchers applied continuous theta-burst stimulation, a refined form of transcranial magnetic stimulation that allows targeted, short-term modulation of specific cortical regions. Because the effect is transient and reversible, the technique enables researchers to infer causal relationships: if temporarily impairing area A produces a deficit on task T, it is reasonable to conclude that area A normally contributes to task T. This approach offers a powerful way to map function to brain structures and will be valuable for future work in cognitive neuroscience and clinical research.
Context, authorship and disclosure
John Michael is based at the Interacting Minds Centre at Aarhus University and combines conceptual and experimental approaches to study social interaction and social cognition. The study’s authors report no financial or other conflicts of interest. The work is presented as open-access research in Psychological Science, and the authors emphasize that the results document a causal role for premotor regions in action understanding while acknowledging that multiple neural and psychological factors underlie social behavior.
Contact: John Michael – Aarhus University
Source: Aarhus University press release
Image credit: Colourbox (adapted from the press release; no usage restrictions reported)
Original research: Continuous Theta-Burst Stimulation Demonstrates a Causal Role of Premotor Homunculus in Action Understanding — John Michael et al., Psychological Science. Published online February 18, 2014. doi:10.1177/0956797613520608
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