Is ASD a disease of the Cerebellum?
Symptoms of autism spectrum disorder (ASD) involve deficits in higher-order cognitive function and often manifests as a social learning disability. The cerebellum’s role in motor movements and balance has been explored in great detail over the past decades, but recent attention has been focused on its involvement in cognitive function, such as emotion regulation. Most studies, therefore, focus on assessing the size, density, and the number of neurons in the cerebellum.
Consistent with findings of other brain regions, studies show ASD subjects have reduced Purkinje cells and reduced cerebellar volume. Purkinje cells are cells found in the cerebellum – they have long extensive dendrites which makes them morphologically unique. They are inhibitory cells; thus, reduced numbers of Purkinje cells due to abnormalities during development may lead to excess firing in the cerebellum. Purkinje cells are also the only output cells in the cerebellum. As a result, the other leading theory of the effects of reduced cerebellar volume is the lack of Purkinje cells or dysregulation of the neural circuitry may lead to a disconnection with the rest of the brain. Studies show that the cerebellum projects to regions such as the prefrontal cortex. If the cerebellum-prefrontal cortex circuit is disturbed or altered, it may adversely impact cognitive functions. The cerebellum also projects to the ventral tegmental area, which contains cells activated by the neurotransmitter dopamine. These dopaminergic cells also ultimately terminate in the prefrontal cortex, so disruptions of this circuit will also have effects on the prefrontal cortex and influence cognitive functions. Many studies have found that the prefrontal cortex plays an important role in ASD, so neuropathology of the cerebellum may also have strong implications in ASD as well.
The cerebellar-prefrontal cortex is an especially important pathway to consider. Mice studies show that cerebellar damage significantly affects the release of dopamine in the prefrontal cortex. Dopamine is a hormone that has been found to affect a wide range of functions such as balance and mood. Additionally, case studies show that the number of Purkinje cells is correlated with cognitive deficits similar to those seen in ASD. The role of the cerebellum and its role in ASD must continue to be investigated. A better understanding of the direct effects of cerebellar deficits on ASD may lead to earlier diagnosis and better treatments.