Visuomotor Interhemispheric Information Transfer in Autism

Background: It has been widely speculated that autism is associated with an atypical state of regional integration, the mechanism by which spatially separated neural processing centers exert mutual influences. This notion has gained support from the growing evidence of atypical white matter microstructural integrity in autistics involving the pathways underlying both intra- and inter-hemispheric information transfer. This evidence of atypical structural connectivity suggests that tasks requiring information transfer among widely distributed neural processing centers would be associated with detectable behavioral differences when comparing autistic and non-autistic samples performing tasks engaging processing centers in both hemispheres.

Poffenberger was the first to demonstrate that the simple reaction time (RT) to a stimulus presented laterally in the visual periphery is faster when the principally involved visual and motor cortical areas are in the same hemisphere than when they are in opposite hemispheres. Since then, there have been numerous studies utilizing this paradigm to study the mechanisms of interhemispheric information transfer. The task is used specifically to derive measures of the inter-hemispheric transfer time (IHTT) by comparing task conditions requiring interhemispheric transfer to those that do not.

Objectives: Our goal was to determine whether autistics would exhibit atypical performance on the Poffenberger task, consistent with the notion that atypical structural connectivity would be associated with atypical IHTT.

Methods: We compared groups of autistics and  non-autistics, matched on IQ, sex and age. The task was a simple reaction time paradigm requiring responses to lateralized visual stimuli collected over the course of 600 trials. The IHTT was estimated from differential response timing (with the right or the left hand) following presentation of brief visual stimuli in the left or right lateral visual field, reflecting the additional time needed for the information to move among the participating regions.

Results: The mean simple response time did not differ significantly between groups. Within groups, there was no difference in the mean response time grouped by response hand or visual field. However, the estimated IHTT was found to be significantly different in the autistic and non-autistic groups, with the autistic group exhibiting lower IHTTs and much higher IHTT variability.

Conclusions: The reduced and more variable IHTT in the autistic group is consistent with the characterization of autism as a state of atypical regional functional integration. While the autistic and non-autistic groups performed the task with equivalent overall speed and accuracy, the task conditions requiring information transfer between the hemispheres were associated with more variable performance in the autistic group, suggesting that underlying developmental differences in white-matter microstructure might result in autistics adopting different processing strategies when confronted with tasks that require transmission of sensory information from one hemisphere to motor control systems in the opposite hemisphere.