Cognition and behavior: Response to emotions linked to autism
These differences could be mediated by the cannabinoid receptor 1, or CNR1, which is involved in reward processing. Genetic variants in this gene predict how long typically developing individuals look at happy faces, reports another study published 29 June in Molecular Autism2.
Together, the two papers suggest that an individual's response to happy faces is an endophenotype — a feature present in both people with the disorder and unaffected family members that indicates an underlying genetic risk factor for autism.
Several studies have shown that individuals with autism have problems identifying faces and recognizing emotions. Studies have linked these differences with altered activity in what researchers call the 'social brain' network, which includes the superior temporal sulcus and the fusiform face area.
In the first study, 40 teenagers with autism, 40 healthy siblings and 40 typically developing controls looked at a series of images of happy, neutral or fearful faces, as well as blank images, while researchers monitored their social brain activity using functional magnetic resonance imaging, or fMRI.
Controls show a heightened brain response to happy faces compared with neutral ones, but this response is dampened in teenagers with autism, the study found. Unaffected siblings have a response halfway between the two groups.
By contrast, all three groups show a similar rise in brain activity when looking at neutral faces compared with blank images, suggesting that the effect does not result from a general lack of interest in faces. Teenagers with autism also respond similarly to fearful and neutral faces.
In the second study, researchers used gaze-tracking software to measure how long 30 typical individuals look at faces with happy, sad, angry, disgusted or fearful expressions.
A previous study by the same group showed that individuals with certain genetic variants in CNR1 have more activity in the striatum — a brain region that mediates rewards — when looking at happy faces compared with those who carry other variants3.
Individuals with the CNR1 variants associated with the most activity in the striatum look at happy faces longer than at those with other expressions, the new study found.