Study finds no differences in cerebellar volume in people with autism after controlling for macrocephaly, IQ, and age.

A review of: CLEAVINGER, H.B., BIGLER, E.D., JOHNSON, J.L., LU, J., McMAHON, W., LAINHART, J.E. (2008). Quantitative magnetic resonance image analysis of the cerebellum in macrocephalic and normocephalic children and adults with autism. Journal of the International Neuropsychological Society, 14(03) DOI: 10.1017/S1355617708080594

As I do my weekly literature search on Autism Research for Translating Autism, I noticed a number of forthcoming manuscripts about the role of the cerebellum in Autism. I will likely review some of these new studies and decided to start with Cleavinger et al (2008) MRI examination of cerebellum in children and adults with autism.

The cerebellum is located on the lower back region of the brain and traditionally it has been implicated in the integration of sensory information and the coordination of movement. However, more recent investigations have determined that the cerebellum is also active in various higher-order functions such as language, emotion, and cognition. In the past, studies looking at differences in the cerebellum of people with and without autism have provide mixed results with some showing increased volume in people with autism, while others show no difference, or decreased volume. One possible explanation for these conflicting findings is that people with autism often vary in degree of macrocephaly (large head size) which may affect the results if the samples studied included individuals with and without macrocephaly. To address this question the authors of this study examined 4 groups: a) people with autism and macrocephaly (N=13) b) people without autism and macrocephaly (N=8) c) people with autism and without macrocephaly (N=28) and c) people without autism and without macrocephaly (N=16). In general, after controlling for macrocephaly, age, and IQ, no statistically significant differences in cerebellar volume were found, although a trend was observed in that people with autism who also had macrocephaly showed smaller cerebellar volume as compared to similar macrocephalic individuals without autism. This trend is important because the ‘non-significant’ differences reported here are likely due to the small sample size and unequal group size, which affects the statistical power of the analysis (making it more difficult to show statistical significant differences even when such differences actually exist). But even if the ‘non-differences’ result is replicated and in fact no differences in cerebellar volume exist between these groups, does this mean that the cerebellum is not implicated in autism? Not at all. Here again I touch the issue of how we should avoid reaching conclusions that go beyond what the data tell us. These results only speak to the size of the cerebellum, suggesting no apparent morphological differences. These results however, do not speak to possible anomalies in the functioning of the cerebellum, which may or may not be present in autism.

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