Brain Advance Access published online on September 26, 2008
Brain, doi:10.1093/brain/awn226
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Acquisition of internal models of motor tasks in children with autism
1Kennedy Krieger Institute, Baltimore, MD and 2Laboratory for Computational Motor Control, Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, USA
Correspondence to:
Stewart Mostofsky, MD, Developmental Cognitive Neurology, Kennedy Krieger Institute, 707 North Broadway, Baltimore, MD 21205, USA E-mail: mostofsky{at}kennedykrieger.org
Children with autism exhibit a host of motor disorders including poor coordination, poor tool use and delayed learning of complex motor skills like riding a tricycle. Theory suggests that one of the crucial steps in motor learning is the ability to form internal models: to predict the sensory consequences of motor commands and learn from errors to improve performance on the next attempt. The cerebellum appears to be an important site for acquisition of internal models, and indeed the development of the cerebellum is abnormal in autism. Here, we examined autistic children on a range of tasks that required a change in the motor output in response to a change in the environment. We first considered a prism adaptation task in which the visual map of the environment was shifted. The children were asked to throw balls to visual targets with and without the prism goggles. We next considered a reaching task that required moving the handle of a novel tool (a robotic arm). The tool either imposed forces on the hand or displaced the cursor associated with the handle position. In all tasks, the children with autism adapted their motor output by forming a predictive internal model, as exhibited through after-effects. Surprisingly, the rates of acquisition and washout were indistinguishable from normally developing children. Therefore, the mechanisms of acquisition and adaptation of internal models in self-generated movements appeared normal in autism. Sparing of adaptation suggests that alternative mechanisms contribute to impaired motor skill development in autism. Furthermore, the findings may have therapeutic implications, highlighting a reliable mechanism by which children with autism can most effectively alter their behaviour.
Key Words: reach adaptation; prism adaptation; motor control; autism
Abbreviations: HFA, high-functioning children with autism; LI, learning index; PD, perpendicular displacement; PRI, perceptual reasoning index; TD, typically developing
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Received March 13, 2008. Revised August 18, 2008. Accepted August 27, 2008.
*Present address: University of Utah, USA
Present address: The Ben Gurion University, Israel