Neurons in the fusiform gyrus are fewer and smaller in autism

Abnormalities in face perception are a core feature of social disabilities in autism. Recent functional magnetic resonance imaging studies showed that patients with autism could perform face perception tasks. However, the fusiform gyrus (FG) and other cortical regions supporting face processing in controls are hypoactive in patients with autism. The neurobiological basis of this phenomenon is unknown. Here, we tested the hypothesis that the FG shows neuropathological alterations in autism, namely alterations in neuron density, total neuron number and mean perikaryal volume. We investigated the FG (analysing separately layers II, III, IV, V and VI), in seven post-mortem brains from patients with autism and 10 controls for volume, neuron density, total neuron number and mean perikaryal volume with high-precision design-based stereology. To determine whether these results were specific for the FG, the same analyses were also performed in the primary visual cortex and in the cortical grey matter as a whole. Compared to controls, patients with autism showed significant reductions in neuron densities in layer III, total neuron numbers in layers III, V and VI, and mean perikaryal volumes of neurons in layers V and VI in the FG. None of these alterations were found in the primary visual cortex or in the whole cerebral cortex. Although based on a relatively small sample of post-mortem brains from patients with autism and controls, the results of the present study may provide important insight about the cellular basis of abnormalities in face perception in autism.