Autism and Excess Neurons

March 31, 2012 § Leave a comment

Autism appears within the first three years of an individual’s life. It critically compromises the normal development of social and communication skills in the brain. A study performed by researchers at the University of California, San Diego Autism Center of Excellence, found that Autistic males with excessive brain growth also have an abnormal surplus of neurons. These excess neurons are found in the areas of the brain that are linked to social, communication and cognitive development.

Cortical cells are a type of cell that is present in the brain before birth. Children with Autism have a 67% excess of these cortical cells. According to Eric Couchesne, Ph.D., professor of neurosciences at the UC San Diego School of Medicine, and director of the Autism Center of Excellence, these findings suggest that the disorder is a result of prenatal processes gone askew.

In 2003 Couchesne’s team published their findings about the origin of the disorder in JAMA. The team linked Autism to the occurrence of an undersized head circumference at birth, followed by a sudden excess growth within the first year of life.

Relying on the direct cell counting method, a new theory about the possible causes of Autism has been confirmed. Couchesne and his colleagues took seven boys with Autism and six normally developing boys, aged 2 to 16, and compared post-mortem tissue from their prefrontal cortex. The prefrontal cortex is the outermost layer of the brain’s cortical. One third of this cortical grey matter – a major component of the central nervous system – is compromised. This is the part of the brain that is responsible for language and communication, and social and cognitive functions. Again, these are the functions most affected by Autism.

Couchesne observed that, “Brain imaging studies of young children with Autism have shown overgrowth and dysfunction in the prefrontal cortex as well as other brain regions. But the underlying cause at the level of brain cells has remained a mystery. The best guess was that overgrowth of prefrontal cortex might be due to an abnormal excess of brain cells, but this had never been tested.”

His team conducted a study to test this hypothesis. They found that in the prefrontal cortex of children with Autism was a 67% excess of neurons compared to the control subjects. The brains of Autistic children were also found to weigh more than those of typically developing children of the same age. All this was found by using an advanced computerized analysis system developed by co-investigator Peter Monton, Ph.D., of the University of South Florida, along with blinded anatomical and cell count measurements.

Couchesne maintains that, “Because new cortical neurons are not generated after birth, the increase in neuron numbers in children with Autism points to prenatal processes.” He went on to explain that proliferation of neurons is exponential between 10 and 20 weeks of gestation, and that at this point in foetal development it normally results in an overabundance of neurons. However, in the third trimester and early life of an infant approximately half of those neurons are removed. This is called ‘cell death,’ otherwise known as ‘apoptosis.’ A failure in early developmental key processes creates a large pathological excess of cortical neurons.

As expected, an excess amount of brain cells was found in each Autistic child involved in the study. Although not every Autistic child will experience this, the study suggests that an abnormal excess of cells is quite common among children with Autism. If future research can discover why this excess exists in the first place, it will have a large impact on our understanding of Autism, and possibly lead to the development of new treatments.

Potential avenues for future study include molecular and genetic mechanisms involved in merging normal cell attrition, or regulating the early production of neurons, which occur in late pregnancy and early infant life.

Sources

Encyclopedia, A. M. (2010, April 26). Autism. Retrieved from PubMed Health: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002494/

Kain, D. (2011, November 8). Autism Linked with Excess of Neurons in Prefrontal Cortex. Retrieved from Neuroscience News.com: http://neurosciencenews.com/autism-linked-excess-neurons-prefrontal-cortex/

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