Cerebellar contributions to autism spectrum disorders

The pathophysiology of autism appears to encompass a number of different brain structures and systems. However, the most consistent site of neural abnormality in autism is the cerebellum. Postmortem investigations have reported a variety of anomalies, most notably a reduction in the number of Purkinje neurons. Additionally, structural neuroimaging studies have shown volumetric changes in the cerebellum, including decreases in gray matter and increases in white matter. Emerging evidence for cerebellar abnormality in autism was paralleled by a revolution in our understanding of normal cerebellar function and cerebellar connectivity, such that the importance of elucidating the contributions of the cerebellum to autism is now clear. In fact, recent brain-behavior correlation studies suggest that cerebellar abnormality may play a more central role in autism than previously thought. At present, it is crucial that we increase our understanding of cerebellar functioning in autism, and functional neuroimaging studies are just beginning to reveal the possible role(s) of cerebellar dysfunction in this disorder. In this review, evidence for cerebellar anatomic and functional abnormality in autism will be delineated. This will be followed by consideration of the implications of cerebellar abnormality in autism. Two major questions will be addressed: (1) how might dysfunction of the cerebellum impact the development of connectivity between the cerebellum and other brain systems, and (2) how might cerebellar dysfunction impact behavior and the symptoms of autism. The paper concludes with a discussion of how cerebellar abnormalities might inform our understanding of the etiology of autism spectrum disorders.