Autistic brains have fewer neurons

The current Autism Unravelled newsletter reports on work carried out by Professor David Amaral and colleagues at the University of California Davis MIND Institute who have been examining the brains of autistic people.

They found that the amygdalae (critical to processing certain emotional reactions, particularly fear) in the brains of autistic people were smaller and more densely packed with neurons. Ongoing research has revealed that there are a decreased number of neurons in the amygdala of autistic brains and especially in the lateral nucleus, the part of the brain which controls perception.

Brain imaging studies have shown that the amygdala develops early in boys with autism and stops growing around the age of eight - whereas in non-autistic boys the amygdala continues to grow until they are 18. Professor Amaral believes it is possible that this early overdevelopment could account for the reduced number of neurons in later life.

He also postulates that excess early activity in the amygdala could produce abnormal fears and anxieties - one of the common traits of autism. ‘The amygdala is involved in appreciating dangerous situations and generating a response to danger, which is probably fear and escape’ - says Professor Amaral. ‘In a pathological state this can lead to anxiety.’

However, Professor Amaral warns that they are still a long way from from knowing anything for sure as they have still only been able to study a handful of autistic brains.

First published January 2007

Click here for more research reports on possible causes of autism

Top of page