Differences in neural reward mechanisms have been hypothesized to play a role in the social symptoms of autism spectrum disorders (ASD). Although a growing number of studies are investigating the neural basis of social and monetary reward in ASD, no studies have yet focused on the neural basis of biological (or primary) rewards. An advantage to studying biological reward is that it does not depend on symbolic representation as monetary reward paradigms do, and therefore may be a better index of non-social reward in people with ASD who may have differences in ability to interpret monetary reward cues. Images of high-calorie foods under conditions of mild fasting have been shown to robustly recruit responses from the reward system in healthy children.
Objectives: To compare children with and without ASD in their neural response to food reward cues.
Methods: A group of 17 children with ASD was compared to a group of 18 children without ASD matched on age, gender, IQ, and body mass index (BMI) in a block design fMRI paradigm during which children were asked to abstain from eating for 4 hours prior to the scan, then to passively view images of appetizing foods. Individual differences in preferred foods and food aversions were taken into account in the choice of food images. Blood oxygenation level-dependent (BOLD) response to these images was compared to that in a visual baseline condition. To ensure attention to the images in the absence of a task, included children had to perform with greater than 75% accuracy in a memory recognition task after the scan. Analyses were limited to a network of regions known to mediate reward response: the nucleus accumbens, amygdala, insula, ventral prefrontal cortex (including orbitofrontal), and anterior cingulate cortex. An uncorrected p value of < 0.005 and a cluster size of at least 10 voxels were used in combination as a threshold for determining regions with a significant BOLD response.
Results:
Very similar patterns of increased BOLD signal to these images in the two groups were found; both groups showed significant clusters of increased BOLD signal in bilateral amygdala, as well as in nucleus accumbens, orbitofrontal cortex, and insula. Direct group comparisons revealed that the ASD group showed a stronger response to food cues in bilateral insula along the anterior-posterior gradient, and in anterior cingulate cortex than the typically developing comparison group, whereas there were no neural reward regions that showed higher activation for the typically developing comparison than for ASD.
Conclusions:
These results suggest that neural response to biological rewards is intact and may even be enhanced in children with ASD.