Background: Numerous functional magnetic resonance imaging (fMRI) studies of the brain-bases of autism have demonstrated altered cortical responses in subjects with autism, relative to typical subjects, during a variety of tasks. These differences may reflect altered neuronal responses or altered hemodynamic response. This study searches for evidence of hemodynamic response differences by using a simple visual stimulus and elementary motor actions, which should elicit similar neuronal responses in patients and controls. Methods: We acquired fMRI data from two groups of 16 children, a typical group and a group with Simplex Autism, during a simple visuomotor paradigm previously used to assess this question in other cross-group comparisons. A general linear model estimated the blood-oxygen-level-dependent (BOLD) signal time course, and repeated-measures analysis of variance tested for potential cross-group differences in the BOLD signal. Results: The hemodynamic response in Simplex Autism is similar to that found in typical children. Although the sample size was small for a secondary analysis, medication appeared to have no effect on the hemodynamic response within the Simplex Autism group. Conclusions: When fMRI studies show BOLD response differences between autistic and typical subjects, these results likely reflect between-group differences in neural activity and not an altered hemodynamic response.
Bibliographical noteFunding Information:
This work was supported by a grant from the Simons Foundation Autism Research Initiative (“Brain Circuitry in Simplex Autism,” Steven Petersen – PI) . John Pruett's effort was supported by K12 EY16336. We thank Sarah Hoertel, for coordinating recruitment, scheduling, and assessments of the subjects. We also thank Kelly McVey for help with recruitment, scheduling, assessing, and scanning subjects. We thank Jen Simmons, Anna Abbacchi, Teddi Gray and others from the Constantino lab for assessing and/or recruiting subjects. We would also like to thank Dan Marcus and his lab for database support.
- Autism spectrum disorders
- Functional magnetic resonance imaging
- Medication effects
- Neurovascular coupling