The amygdala is a small area of the brain which is responsible both for the "fight-or-flight" response and for identifying faces and evaluating social situations. People with autism, new research suggests, may have an unusually large and overactive amygdala. This may be one reason why people with autism are easily overstimulated and have a hard time understanding and managing emotions.
New research at the University of Washington has provided more insight into this phenomenon. According to an article in Newswise:
The new research shows that brain activation in adults with autism remains elevated long after similar brain regions of typically developed adults have stopped being activated when exposed to a series of pictures of human faces. A decrease in activation over time to the same type of information is called neural habituation and is connected with learning, according to Natalia Kleinhans, lead author of the new study and a UW research assistant professor of radiology.“What we are seeing is hyperexcitability or overarousal of the amygdala, which suggests that neurons in the amygdala are firing more than expected,” said Kleinhans, who is associated with the UW Autism Center.
For more on autism and the brain:

Interesting.
except Tristan doesn’t appear to be overstimulated and doesn’t appear to have a problem understanding emotions. Responding appropriately yes, understanding, no.
I wonder if this research shouldn’t be applied more towards the sensory issues many autistics have, rather than to autism itself.
I thought the theory relating the placenta and autism was interesting. When my son was born 5 1/2 years ago, everything went well. I had no issues with my placenta, his birth or anything; and, he was full term and weighed almost nine pounds. A healthy baby boy that I breastfed for a year. I am not sure that I buy the placenta theory, though I do believe that DS’s autism is genetic in origin.