Representation of internal models of action in the autistic brain

Abstract

Children with autism spectrum disorder (ASD) have deficits in motor control, imitation and social function. Does a dysfunction in the neural basis of representing internal models of action contribute to these problems? We measured patterns of generalization as children learned to control a novel tool and found that the autistic brain built a stronger than normal association between self-generated motor commands and proprioceptive feedback; furthermore, the greater the reliance on proprioception, the greater the child's impairments in social function and imitation.

Figure 1

(a) Children held the handle of a robotic arm and played a game in which the objective was to capture animals that had escaped from a zoo. At the start of the trial, the robot moved the child’s arm to a starting posture. Next, an animal would appear at the target location (8 cm). If the child could reach the target in time (0.5 ± 0.05s), the animal would be captured and the child was given points which later could be traded in for a prize. The robot produced a velocity dependent curl force field. Learning took place in the left posture (T1) and generalization was quantified in the right posture (T2, identical joint motion as T1; T3, identical hand motion as T1). The target sequence was random. Study was approved by the local IRB. Written consent was obtained from a parent/guardian and written assent was obtained from the children. (b) Across subject mean ± SEM hand paths during the last trial of the baseline block and the first and last trials of the learning block. Red lines are for autistic children. (c) Movement error mean ± SEM for T1, as quantified through maximum lateral hand deviation; negative value indicates hand deviation to the left. The filled circles indicate trials in which the robot perturbed the hand and the unfilled circles indicate error-clamp trials. (d) In error-clamp trials, the robot produced a channel from the start position to the target, essentially eliminating movement errors. We measured the force that the child produced against the channel walls. (e) The average of force in the first five error-clamp trials in the test block.

Figure 2

(a) Autism Diagnostic Observation Schedule is a standardized interview and observational assessment of social, communicative, and stereotyped behaviors used for diagnosis of autism. The x-axis represents the force produced for T3. (b) The Social Responsiveness Scale, a measure of social anxiety/avoidance in naturalistic settings, was scored for most of the TD (10/13) and ASD (13/14) children. (c) Imitation was measured by asking the child to reproduce a sequence of 36 actions (performed one at a time), some meaningful and others meaningless . The x-axis represents the force produced during the test of generalization (T3 minus T2).