A core symptom of autism spectrum disorders (ASD) is social impairment. A genetic variation has been identified which is associated with the symptom of social impairment, called the S allele of the serotonin transporter-linked promoter region. People who have one or two copies of the S allele in their genome tend to have increased social impairment, compared to those who have other genotypes. Neurologically, social deficits are thought to be related to overactivity of neurons in a specific brain regions, the amygdala and the ventral prefrontal cortex (vPFC). In this study, Dr. Monk and colleagues will examine the connection between the S allele and neural activity in the amygdala and vPFC, and how these factors contribute to social impairment. Using functional magnetic resonance imaging (fMRI), a method of visualizing neural activity in specific brain regions, they will examine the amygdala and pVFC in subjects while they perform a social task, such as recognizing emotions in facial expressions. The subjects will be chosen from four groups: autistics with two copies of the S allele or no copies of the S allele, and typical, non-autistic individuals with two copies of the S allele or no copies of the S allele. This experiment will allow the researchers to determine whether this genetic variant is associated with overactivity in the amygdala and pVFC, and how this relates to the severity of social impairment in both autistics and non-autistics. Linking genotype to the abnormal activity of neural pathways responsible for social impairments will be important in understanding the causes of this debilitating symptom of autism.