Autism has become an industry these days, as the above picture suggests. The topic has entered public awareness, but well tested experimental results are indiscriminately mixed with old theories that should have given up the ghosts given more recent work, and the crackpot notions that arise because people with good hearts want answers. As I'm digesting these articles I thought I'd summarize some of the ones I find more interesting for those of you who care. Some of them are more global theories about what might lie behind the syndrome, others look at highly specific symptoms, or characteristics. I'll do one of each today. I'll define any terms that seem potentially difficult or are usually referred to in the media too generally (as in the term 'autism' itself), and I'll try to use layman's language. If I can find free sources with greater detail I'll link to them, otherwise I'll just reference them.
Autism is a developmental disorder that is characterized by a certain number of impairments in social and emotional behaviors, delays in language development leading to impairments in verbal and non-verbal communication, and a restricted repertoire of interests and activities present from early childhood. The range of autistic disorders spans intelligence and language abilities from high functioning to severely impaired.
Asperger's syndrome is on the same spectrum of syndromes as autism but it is distinguished from it based largely on a lack of language delay, if one only considers literal language skills. Yet people with AS have difficulty in what M. D. Rutherford and Simon Baron-Cohen term "reading the mind in the voice," understanding more hidden and subtle meanings that most of us learn to perceive automatically from a fairly early age. It has been thought that those with AS lack that ability, because they have problems in producing and perceiving prosody . Prosody can be thought of as the music of speech. It comprises the rhythm, intonation and pitch that colors words and phrases to convey intent, mood and function. (For those interested in detailed background on this see McCann & Peppe, 2003 and Rutherford et. al. 2002).
These effects were primarily based on reports of patients with AS - which is not insignificant, but it is difficult to measure individual accounts, when the brains and ears that are perceiving the speech each have their own individual differences producing unique subjective experiences. The study I read (Neurophysiological evidence for cortical discrimination impairment of prosody in Asperger syndrome - Kujala et al, 2005) compared the responses of "normally developing" women to women with AS in their neural responses to spoken sounds with varying emotional content. Their results confirm the prosody processing abnormality through an objective measure - an EEG recording (which measures electrical activity of the brain from the scalp) and delineates specific differences in how the women with AS process prosody:
1. The subjects notice fewer differences in prosody
2. The differences they do notice produce less noticeable effects in the brain but for a longer duration (in relatively small units - milliseconds)
3. The wave demonstrating the effect reveals that the impairment occurs at a point early in auditory processing (a low-level or fundamental deficit may be the root of the problem).
4. The waves recorded at the time the speech was heard seem to originate from a different place in the brain than those of the normal subjects to whom the women were compared. This does not necessarily imply a "cause," of autism, it could be an effect. I'll explain: given the fact that autistic spectrum brains are different from others and given the fact that autistic people exist in the same world as we do and attempt to accomplish many (but not all) of the same things, they sometimes end up compensating by employing different combinations of brain structures - i.e. they wire things a little differently - than others do.
The second article looks at another popular neuroscience phenomenon - mirror neurons - and discusses a theory connecting autism spectrum disorders with a dysfunction in the "mirror neuron system."
Mirror neurons are a type of nerve cell that fire both when someone performs a given action and when they observe that same action being performed by someone else. They are thought to match observed behavior of another with executed behavior by oneself. Many think this mechanism helps us automatically give meaning to others' intentions and actions. It is a fairly recent theory that a dysfunction of this system could result in the range of impairments seen across the autistic spectrum which include problems in imitation, social interaction, and theory of mind (the ability to attribute mental states, desires and intents to others that can be different from our own). A further development of this theory suggests a connections between the mirror neuron system and the limbic system (a brain area associated with emotion) via the insula which allows us to interpret the meaning of observed emotions in others. Here's one good recent article Iacoboni & Dapretto, 2006 on the theory from Nature Neuroscience.
The article I read - Understanding emotions in others: mirror neuron dysfunction in children with autism spectrum disorders - Dapretto et al, 2006 summarizes this theory, and performs a study of their own comparing "normally developing" and autistic children observing and imitating emotional expressions from photographs adding two additional pieces of information. They measure their ability to measure and imitate as well as scanning the brain with fMRI, which creates a picture of relative activity of brain areas at the time of a specific event. They saw the following:
1. Both autistic children and controls were capable of observing and imitating emotional expressions, but children with autism did not show increased activation of the brain area normally associated with mirror neuron activity whereas the controls did
2. The less activity observed in the mirror neuron system brain area, the more severe the social impairments of the subjects - which they conclude could indicate that a dysfunctional mirror neuron system might cause the social deficits seen in autism.
It's an excellent and short article but it's too soon to judge, however, if one is compelled by the concept of mirror neurons and the described link to emotional understanding, it's a short leap to connecting their dysfunction to a syndrome so characterized by social deficits. There are many other good articles on this subject. There's this one for the general reader by the omnipresent Vilayanur Ramachandran from Scientific American. And here are two more technical ones from various scientific journals:
Oberman & Ramachandran, 2007
Oberman, et al, 2005