Autism is a disorder that presents in early childhood and is characterized by deviance and delays in development of reciprocal social interaction, communication, and the child’s range of interests and activities. Investigations of brain-behavior mechanisms contributing to autism have thus far principally relied on approaches adapted from adult lesion-based models in which existing cognitive and behavioral domains (e.g., attention, perception, executive function) are examined. Despite the clear developmental nature of autism, relatively few studies have focused on detailed examination of neural mechanisms central to learning. Such an approach would be critical to understanding the developmental basis of autism and might also lead to improvements in therapeutic intervention.
Beyond the social and communicative skill impairments that comprise the core diagnostic features of autism, numerous studies have revealed motor skill deficits in autism. Parallels between social/communicative and motor development in autism may in large part be attributable to overlap in procedural learning mechanisms underlying acquisition of these motor and social/communicative skills. In contrast to declarative learning systems that mediate acquisition (“memorization”) of facts, procedural learning is the process by which the brain acquires a wide range of skills - not only basic motor skills, but also more complex goal-directed skills, including those critical to socialization and communication. During procedural learning of motor skills, internal models of action are built that associate one’s own motor commands (mediated by frontal motor/premotor cortex) with sensory feedback (mediated by posterior, principally parietal, cortex); subcortical basal ganglia and cerebellar input serves to reinforce and optimize selection of the actions appropriate to achieving the goal. In forming these models linking perception to action, the brain not only learns how to execute these skills but also to learns how to interpret the meaning of these actions when performed by others. Based on the deficits observed in autism, these procedural “action-based” mechanisms may therefore be crucial to understanding developmental processes contributing to core autism-associated impairments in social skills and social cognition.
Motivated by these principles, we have been pursuing detailed examination of motor control and learning in children with autism spectrum disorder (ASD). Our studies of motor learning have led to an interesting observation – There is a fundamental difference in how children with ASD learn a new action; during motor learning, children with autism build a stronger than normal association between motor commands and intrinsic proprioceptive feedback from their own “inner world,” and a weaker than normal association between the same commands and extrinsic visual feedback from the world around them. This bias towards the inner world is consistent with descriptions of autism dating back to Kanner’s original thesis emphasizing difficulty with forming inter-actions that relate to the outside world and a tendency to develop a limited repertoire of behavior that is “internally driven”. Our findings that during motor learning children with ASD place a greater than normal reliance on their own proprioception while discounting visual consequences in the extrinsic world suggests a rationale for why they are impaired in their ability to acquire models of action through visually-based imitation, and why there are less able to understand and interpret the meaning of visually-observed social and communicative behavior of others.
Following up on these findings, we have been using structural and functional imaging methods to investigate the brain basis of these autism-associated alterations in motor learning; our initial findings suggest that children with autism show decreased visual-motor connectivity that are predictive of measures of autism severity.
Crucially, we are now applying these findings to pilot novel methods for therapeutic intervention that both: 1) “play to the strengths” of autism, leveraging proprioceptive feedback to improve important motor skills (e.g., handwriting) in children with ASD, and 2) alter presentation of visual feedback so as to help children with ASD improve their ability to learn through imitation.