David Amaral and Cynthia Mills Schumann of the University of California, Davis conducted a survey on the number of neurons in the amygdala of nine autistic males and 10 nonautistic males ranging from ages 10 to 44. Their findings have been published in The Journal of Neuroscience.
Counting them painstakingly under a microscope revealed far lower number of neurons in the amygdala which is the area of the brain associated with fear and memory.
Amaral notes "This is the first quantitative evidence of an abnormal number of neurons in the autistic amygdala. We were able to analyze more than double the number of previously examined postmortem brains, none of which had seizure disorders or any major neurological disorder other than autism."
Amaral and Schumann counted neurons with a three-dimensional probe at high magnification. It was found that although the amygdala volumes in all the brains was about the same, the autistic males as a group had almost 1.5 million fewer neurons than their peers.
Earlier brain imaging studies have shown that autistic boys develop adult-size amygdala by they were eight years old, compared to late adolescence for other young males. It is still left to be seen whether other brain regions in autistics might face a neuron deficit as well.
Schumann says, "One possibility is that there are always fewer neurons in the amygdala of people with autism. Another possibility is that a degenerative process occurs later in life and leads to neuron loss. More studies are needed to refine our findings." Their results appear in a paper published today in.