A NY Times article summarizing current knowledge of the insula, a small interior lobe of the brain’s cerebral cortex, was inspired by the recent finding of its connection to nicotine addiction, and never mentions the word “autism.” But certain parts brought that word to my mind:
The frontal insula is where people sense love and hate, gratitude and resentment, self-confidence and embarrassment, trust and distrust, empathy and contempt, approval and disdain, pride and humiliation, truthfulness and deception, atonement and guilt.
People who are better at reading these sensations — a quickened heart beat, a flushed face, slow breathing — score higher on psychological tests of empathy, researchers have found.
Lack of empathy, of course, is one of the major symptoms of autism. The term “autism” seems generally to refer now to a continuum of conditions progressing toward lower and lower empathy with other humans, with the most extreme cases resulting in apparent complete withdrawl from the social world. There are also functioning autistics, however, with the condition known as Asperger’s Syndrome. The prime example of this is Temple Grandin, a professor of Animal Sciences at Colorado State whom Oliver Sacks has profiled. Her primary symptom according to Sacks is a lack of empathy, or inability to interpret or imagine what others are thinking and feeling. There are likely plenty of people moving about in society undiagnosed with any “condition” who are better or worse at this. My belief is that it is a long continuum along which all people exist, and some (arbitrary?) point towards the lower-empathy end is considered to be on the edge of normality.
I found a couple of papers, one of which examines the relation of the insula to empathy, also without mentioning autism:
Neural mechanisms of empathy in humans: A relay from neural systems for imitation to limbic areas. Laurie Carr, Marco Iacoboni, Marie-Charlotte Dubeau, John C. Mazziotta, and Gian Luigi Lenzi, 2003. PNAS USA 100:5497-5502:
Further, fronto-temporal areas relevant to action representation, the amygdala, and the anterior insula had significant signal increase during imitation compared with observation of facial emotional expression.
A more recent paper does find a correlation between autism and reduced activity in the insula:
Understanding emotions in others: mirror neuron dysfunction in children with autism spectrum disorders. Dapretto et al, 2006. Nature Neuroscience 9:28-30
Are brain differences in “autistic” people caused by genetics or environment? Boy, is that a hot button issue. There are still plenty of people out there who blame vaccines for their children’s autism, and papers saying there is no observable effect, but once again the problem understanding this might be the difficulty the medical profession has in admitting there may be such a thing as an environment-by-genetics interaction. It isn’t nature or nurture, folks – it’s how the two interact. If some people’s brains are sensitive to a certain environmental trigger, then exposure to some compound or other could actually cause a condition in some people while not causing it in others. (Does this mean you should avoid vaccines? Of course not! The probability of your child dying of a typical childhood disease is hundreds or thousands of times higher than the probability that any serious side-effect will occur – even the known ones.) A typical large medical study that lumps all genotypes together to look for an environmental effect will never find it under these conditions. An analogous problem is with chemotherapy, which researchers are finally discovering works such a small part of the time with most cancers because a certain type of cancer might involve a dozen different mechanisms, for perhaps one or two of which a given chemotherapy will actually, predictably work.
Of course there are cases in which autism clearly has a large genetic component, such as in the case of a family mentioned by Sacks with two Asperger’s parents, and three kids all with autism, albeit at different locations on the continuum. My own pet theory, substantiated by absolutely no evidence, is that the higher levels of autism being observed largely in California in the most recent generation are due to so many computer geeks making a ton of money in silicon valley, and thus having an opportunity to reproduce previously unrealized due to their poor social skills.
Obviously the brain is incredibly complex, and the insula appears to be just one link in a chain involving the limbic system and inferior frontal gyrus (also part of the cerebral cortex). But those fighting cigarette addiction might want to think twice about jamming an ice pick in there.