fMRI Evidence for Generalised Arousal as a Substitute for Early Selection in Autism during Conditions of Shifting Visual Spatial Attention


Matthew Belmonte and Deborah Yurgelun-Todd


November 9-10, 2001
San Diego, California

ABSTRACT

Physiological and behavioural results have pointed to sensory hyperarousal and impairment in shifting attention in autism. To investigate the physiological basis of these characteristics we applied fMRI during shifting of visual spatial attention. Subjects viewed coloured squares flashed at 9Hz in the left and right upper quadrants. A red square in the attended location cued not only an overt behavioural response but also a covert shift of attention to the opposite location. Single-shot T2*-weighted images were acquired at 1.5T. Voxelwise differences between the task condition and a rest condition were assessed for significance using a permutation test. Foci of task activation were then used in combination with anatomical images to define a priori regions of interest for correlation with behavioural data within individuals. Results in normal subjects, reported separately, include an inferior occipitotemporal activation contralateral to the attended field (t(14)=3.44, p=0.0040), as well as a posterior intraparietal activation ipsilaterally (t(14)=2.55, p=0.0229) which may reflect active suppression of irrelevant stimuli. Preliminary data on autism show an absence of lateralised attentional activity in the occipitotemporal region, and a high level of lateralised attentional activity intraparietally. We suggest that in autism during conditions that demand rapid change in attentional set, generalised arousal substitutes for impaired early selective attention, leaving irrelevant stimuli to be suppressed at a later stage.
 Supported by the National Alliance for Autism Research.