Friday, May 21, 2010
Franklin Hall B Level 4 (Philadelphia Marriott Downtown)
9:00 AM
D. Crocetti
,
Laboratory for Neurocognitive and Imaging Research, Kennedy Krieger Institute, Baltimore, MD
P. Srinivasan
,
Laboratory for Neurocognitive and Imaging Research, Kennedy Krieger Institute, Baltimore, MD
J. Izawa
,
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD
R. Shadmehr
,
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD
S. H. Mostofsky
,
Laboratory for Neurocognitive and Imaging Research (KKI), Departments of Neurology and Psychiatry (JHU), Kennedy Krieger Institute, Johns Hopkins University School of Medicine, Baltimore, MD
Background: There is increasing evidence suggesting that autism is associated with impairments in motor skill development (e.g., Jansiweicz et al., 2006; Mostofsky et al., 2006; Dzuik et al., 2007; Dowell et al., 2009). When learning motor skills, internal models of action are formed whereby associations are built between motor commands (mediated by motor and premotor cortices) and sensory feedback (mediated by somatosensory and posterior parietal cortices). Production of motor commands is based on the brain’s ability to interpret this sensory (visual and proprioceptive) input. Recent findings (Haswell et al., 2009) suggest that during motor learning, children with autism spectrum disorder (ASD) build a stronger than normal association between motor commands and proprioceptive feedback and a weaker than normal association between the same commands and visual feedback. This is consistent with imaging and postmortem studies (Casanova et al., 2006; Herbert et al., 2004) revealing an over-expression of short-range axons in children with autism including axons connecting the primary motor and somatosensory cortices (i.e. primary sensorimotor cortex), where activity fields of neurons are in the intrinsic coordinates of proprioception (Scott et al., 1997).Objectives:
To examine the association between white matter connections localized within the primary sensorimotor cortex (SM1) and autism-associated differences in skill performance and learning.Methods: Diffusion tensor imaging was acquired in 17 children with ASD and 18 typically-developing (TD) children. A white matter parcellation atlas within MRIStudio (Mori et al., 2008) was used to measure mean fractional anisotropy (mFA) within primary somatosensory (postcentral gyrus) and primary motor (precentral gyrus) regions. For a subset of these subjects (9 ASD, 6 TD) motor learning was assessed using a reaching task that involved learning an internal model of a novel tool, a robotic arm. The objective of the task was to move the arm to a video-displayed target within a set time-window. The task was comprised of three targets: Target 1 assessed task learning, Target 2 assessed generalization to extrinsic visual coordinates, and Target 3 assessed generalization to intrinsic proprioceptive coordinates.Results: Group analysis revealed a trend (p=0.09) for decreased FA in right + left somatosensory cortices (S1). Analysis revealed that for children with ASD, mFA in left + right SM1 correlated with increased force for Target 3 (R=-0.70, p=0.03), such that lower SM1 FA predicted the autism-associated tendency to rely on proprioceptive feedback during motor learning. No significant correlation was observed in TD controls.Conclusions:
The findings reveal that for children with ASD, their tendency to excessively rely on proprioceptive, rather than visual, feedback during motor learning is associated with lower FA in primary sensorimotor white matter. The findings suggest that disorganized patterns of localized white matter connections within SM1 may contribute to abnormal formation of action models in autism. We have reported (Dziuk et al., 2007; Haswell et al., 2009) that autism-associated abnormalities in motor skill learning and skill performance strongly correlate with measures of the core social deficits that define autism. Our findings here therefore support proposed models suggesting that the behavioral impairments of autism are associated with disorganized patterns of white matter connectivity.
