Oculomotor evidence for neocortical systems but not cerebellar dysfunction in autism

Abstract

Objective: To investigate the functional integrity of cerebellar and frontal systems in autism using oculomotor paradigms.

Background: Cerebellar and neocortical systems models of autism have been proposed. Courchesne and colleagues have argued that cognitive deficits such as shifting attention disturbances result from dysfunction of vermal lobules VI and VII. Such a vermal deficit should be associated with dysmetric saccadic eye movements because of the major role these areas play in guiding the motor precision of saccades. In contrast, neocortical models of autism predict intact saccade metrics, but impairments on tasks requiring the higher cognitive control of saccades.

Methods: A total of 26 rigorously diagnosed nonmentally retarded autistic subjects and 26 matched healthy control subjects were assessed with a visually guided saccade task and two volitional saccade tasks, the oculomotor delayed-response task and the antisaccade task.

Results: Metrics and dynamics of the visually guided saccades were normal in autistic subjects, documenting the absence of disturbances in cerebellar vermal lobules VI and VII and in automatic shifts of visual attention. Deficits were demonstrated on both volitional saccade tasks, indicating dysfunction in the circuitry of prefrontal cortex and its connections with the parietal cortex, and associated cognitive impairments in spatial working memory and in the ability to voluntarily suppress context-inappropriate responses.

Conclusions: These findings demonstrate intrinsic neocortical, not cerebellar, dysfunction in autism, and parallel deficits in higher order cognitive mechanisms and not in elementary attentional and sensorimotor systems in autism.

Figure 1

Percent of trials on an antisaccade task during which autistic subjects and healthy control subjects failed to suppress reflexive responses to look toward visual targets presented at 8, 16, or 24 deg of visual angle from center fixation in the horixontal plane collapsed across left and right visual fields.

Figure 2

Absolute error of the first saccade (in degrees of visual angle) made after a delay period of 1, 2, 4, or 8 seconds to remembered target locations in an oculornotor delayed-response task by autistic subjects and healthy matched control subjects.