Saccadic Adaptation in Autism

Background: Post-mortem and structural MRI studies have identified cerebellar alterations in autism. Functional impairments associated with these alterations have not been identified. Saccadic adaptation occurs when the oculomotor system adjusts for systematic errors in the accuracy of saccadic eye movements. This process is heavily dependent on cerebellar networks, in particular the vermis. Thus, studies of saccadic adaptation may be useful for assessing the functional integrity of the cerebellum in autism.

Objectives: To examine saccadic adaptation in individuals with autism.

Methods: Fifty-six individuals with autism and 53 age- and IQ-matched healthy controls performed an intrasaccadic target step task known to elicit saccadic adaptation. In this task, targets are displaced to a new location during saccades, and subjects learn to make saccades to where the target will be displaced rather than to the location of the target that elicited the saccade.

Results: Participants in both groups demonstrated similar rates of saccade adaptation over trials. However, individuals with autism showed a pronounced lateral asymmetry of saccade adaptation. During adaptation, the autism group’s saccades were hypometric to the left hemifield (e.g., closer to displaced target) but hypermetric to the right hemifield. Healthy controls did not show this hemifield difference. Additionally, individuals with autism exhibited greater variability in saccade accuracy across trials, indicating failure of the variability-reducing function of the vermis in saccade control.

Conclusions: The alterations in adaptational processes in our autism subjects are similar to those seen in human and animal studies of chronic unilateral cerebellar vermal lesions, and thus indicate a lateralized disturbance of vermal function in autism. Data are consistent with a previous report from our lab (Takarae et al., 2004) suggesting lateralized dysfunction of visual sensorimotor brain systems in autism.