Functional neuroimaging and childhood autism

Childhood autism is now widely viewed as being of developmental neurobiological origin. Yet, localised structural and functional brain correlates of autism have to be established. Structural brain-imaging studies performed in autistic patients have reported abnormalities such as increased total brain volume and cerebellar abnormalities. However, none of these abnormalities fully account for the full range of autistic symptoms. Functional brain imaging, such as positron emission tomography (PET), single photon emission computed tomography (SPECT) and functional MRI (fMRI) have added a new perspective to the study of normal and pathological brain functions. In autism, functional studies have been performed at rest or during activation. However, first-generation functional imaging devices were not sensitive enough to detect any consistent dysfunction. Recently, with improved technology, two independent groups have reported bilateral hypoperfusion of the temporal lobes in autistic children. In addition, activation studies, using perceptive and cognitive paradigms, have shown an abnormal pattern of cortical activation in autistic patients. These results suggest that different connections between particular cortical regions could exist in autism. The purpose of this review is to present the main results of rest and activation studies performed in autism.