Brain Differences in children with Autism: White Matter – Gray Matter

A review of: BONILHA, L., CENDES, F., RORDEN, C., ECKERT, M., DALGALARRONDO, P., LI, L., STEINER, C. (2008). Gray and white matter imbalance – Typical structural abnormality underlying classic autism?. Brain and Development DOI: 10.1016/j.braindev.2007.11.006

The authors of this study discussed the relative inconsistent results from studies trying to examine brain differences in children with and without Autism. For example, although many post-mortem studies have found brain differences, the differences they find vary significantly between studies. The same is true of studies using imaging techniques such as MRI. However, the most consistent finding is an overall larger brain volume in children with autism, leading some researchers to propose deficits in cell pruning as a possible cause of autism (more of this below). In this study the authors used MRI (Magnetic Resonance Imaging) to compare 12 children with Autism (average age 12) to 16 matched typically developing children. The results showed that children with autism had increased generalized bilateral gray matter. Specifically increased gray matter was observed in the cingulated gyrus, caudate, cerebellum, claustrum, cuneus, fusiform gyrus, inferior, middle and superior frontal gyri, inferior and superior temporal gyri, inferior and superior parietal lobules, pre and post-central gyrus, precuneus, putamen, thalamus, insula and occipital cortex. The results also showed decreased generalized bilateral white matter in the cuneus, medial and superior frontal gyri, pre- and post-central gyri, inferior parietal lobule, supramarginal gyrus, cingulote gyrus, middle occipital gyrus, parahippocampal gyrus, and the middle and superior temporal gyri. The authors concluded that their data provides strong evidence for increased gray matter and reduced white matter in children with autism when compared to typically developing kids. Similar results have been used as evidence of the cell pruning theory of autism. This theory indicates that children with autism have an atypical brain development process during early infancy. Specifically, during a typical post-natal period, there is considerable removal of connections between cells in the brain leading to more efficiency in cell connectivity and cell communication. Researchers argue that abnormal brain growth during early development in autism is due to limited pruning of such synaptic connections.