New research suggests that a brain system called the mirror neuron system, previously implicated as being dysfunctional in autism appears to function normally in individuals with autism spectrum disorder (ASD). The study, published by Cell Press in the May 13 issue of the journal Neuron, argues that difficulties in social communication experienced by individuals with ASD are caused by neural abnormalities other than a mirror neuron system dysfunction.
Impaired social interaction is a hallmark of ASD. It has been suggested that this impairment might be due to a dysfunction in the mirror neuron system. Mirror neurons are neurons that are active both when an animal performs an action and when the animal observes the same action being performed by another. In humans, mirror neurons are thought to be critical for our ability to perceive the intentions and goals of others, an ability that individuals with autism find difficult. Previous neuroimaging studies have suggested that ASD individuals may exhibit weaker mirror neuron systems than typical individuals.
"These earlier studies did not assess the selectivity of cortical activity in mirror system areas for particular movements," says lead study author, Dr. Ilan Dinstein. "Movement selectivity is a critical characteristic of the mirror neuron system, necessary for its proposed role in perceiving the intentions of others. To properly perceive the intentions of movements made around us (e.g., waving hello), our brain must represent each different movement with a unique neural response."
To examine the selectivity of mirror neuron system responses, Dr. Dinstein and colleagues used functional magnetic resonance imaging (fMRI) with an "adaptation" protocol. Adaptation is a trick commonly used to assess the selectivity of brain responses to particular stimuli, capitalizing on the phenomenon that selective neural populations decrease their response (adapt) when they are presented repeatedly with their preferred stimulus. In this case, the stimuli were hand movements that were either passively observed or actively executed by participants in the scanner.
Mirror system areas in individuals with ASD exhibited normal adaptation when a particular hand movement was repeatedly observed or executed in comparison to when different hand movements were observed or executed, attesting to their selectivity. "Our experiments targeted a key feature of movement perception not addressed by previous studies--the ability of neural populations in mirror system areas to differentiate between different hand movements," concludes Dr. Dinstein. "The finding that these neural populations respond normally and selectively to particular hand movements argues strongly against a mirror neuron system dysfunction in autism."
The researchers include Ilan Dinstein, New York University, New York, NY; Cibu Thomas, Carnegie Mellon University, Pittsburgh, PA; Kate Humphreys, Carnegie Mellon University, Pittsburgh, PA; Nancy Minshew, University of Pittsburgh, Pittsburgh, PA; Marlene Behrmann, Carnegie Mellon University, Pittsburgh, PA; and David J. Heeger, New York University, New York, NY.