Different Brain Responses to Different Actions: A New Paradigm to Study Action Comprehension in Autism

Background:

The ability to comprehend actions, which is crucial to successful social interactions, is dysfunctional in Autism Spectrum Disorders (ASD). Investigating neural mechanisms underlying this ability is, therefore, of great importance. Previous studies exploring this topic have in some way neglected the social dimension of this ability, using non-social actions as stimuli (e.g. grasping) and passive observations as experimental tasks.

Objectives:

We aimed at investigating brain basis of action understanding in adults and children with and without autism developing a semi-naturalistic paradigm. Using functional magnetic resonance imaging (fMRI), we compared brain activations elicited by actions directed to the participants or requesting a response with actions not demanding a response or directed to another person.

Methods:

The current experiment consisted of a ball tossing game depicted in a series of interactive video clips. Two players performed two kinds of actions: gesturing for a ball (Bid action) or a simple up-and-down arm motion (Motion, control action). Players were turned either toward the subjects (Toward conditions) or to each other (Away conditions, control). In the -Toward conditions participants were instructed to throw the ball, pressing a button, to a player of their choice. The experiment used an event-related design with participants viewing 24 trials of each condition (Bid-toward, Motion-toward, Bid-away, and Motion-away).

Results:

Data from 8 TD (typically developing) adults contrasting Bid-toward to Motion-toward conditions revealed an activation of the right Superior Temporal Sulcus (STS), a brain region underlying action goal understanding. This difference was not evident between the -Away conditions. Furthermore, the interaction of the type of action with the direction of the players resulted in a significant activation of the right Precentral Gyrus (BA6) only between the -Toward conditions. This area belongs to the putative MNS (Mirror Neuron System) that is supposed to participate in action comprehension processes through a resonance automatic mechanism. These data suggest that being the target of a bidding action and not just a passive viewer prompted a deeper processing of action stimuli, enabling the brain to differentiate between distinct actions otherwise processed as the same.

Conclusions:

Having established this paradigm in TD adults, we are now running samples of children with and without autism. Previous studies investigating neural basis of action understanding have shown a diminished activation in STS and in the MNS in children with autism, suggesting these brain structures underpin their difficulties in action comprehension. Hence, we expect STS and Precentral Gyrus will be generally less activated in autistic than in TD children brain. However, considering the results on TD adults, we expect this paradigm will provide more detailed data on the neural activations subserving action comprehension in children with ASD.