J Izawa, SE Pekny,
MK Marko, C Haswell, R Shadmehr, and SH Mostofsky (2011) Autism
Research.
Abstract The brain builds an association between
action and sensory feedback to predict the sensory consequence of
self-generated motor commands. This internal model of action is central to our
ability to adapt movements, and may also play a role in our ability to learn
from observing others. Recently we
reported that the spatial generalization patterns that accompany adaptation of
reaching movements were distinct in children with Autism Spectrum Disorder
(ASD) as compared to typically developing (TD) children. To test whether the generalization
patterns are specific to ASD, here we compared the patterns of adaptation to
those in children with Attention Deficit Hyperactivity Disorder (ADHD). Consistent
with our previous observations, we found that in ASD the motor memory showed
greater than normal generalization in proprioceptive coordinates compared with
both TD children and children with ADHD; children with ASD also showed slower
rates of adaptation compared with both control groups. Children with ADHD did
not show this excessive generalization to the proprioceptive target, but did
show excessive variability in the speed of movements with an increase in the
exponential distribution of responses ( ) as compared with both TD children and
children with ASD. The results suggest that slower rate of adaptation and
anomalous bias towards proprioceptive feedback during motor learning is
characteristic of autism; whereas increased variability in execution is
characteristic of ADHD.