Wednesday, November 9, 2011 - 0 comments

Autism : 5. Explaining Autism’s Variability

by : Uta Frith

BRAIN SCANS show differences in activity between normal
and autistic people. In normal persons reading a story that requires
inferring the mental state of others, the left medial prefrontal
cortex of the brain was active (left). In persons with Asperger
syndrome performing the same task, an adjacent lower
area was active instead (right). The left medial prefrontal cortex
may be a key component of the theory of mind capability.
The astonishing variability in the signs and symptoms of autism is only beginning to be fully appreciated. Some  autistic individuals never develop speech or nonverbal communication, whereas others become fluent and can  pass for normal in social interactions. A screening test that identifies the lack of shared attention, pretend play and eye contact characteristic of autism—developed by Simon Baron-Cohen of the University of Cambridge and his colleagues at Guys Hospital in London—appears to be remarkably successful in predicting autism in children as young as 18 months.

The most severe cases of autism are associated with mental retardation, but IQ does not consistently correlate with abilities and special talents. Some studies report that up to 10 percent of the autistic population has a savant skill—exceptional ability in one area, such as playing the piano, drawing or mathematics. Significantly, almost all savants are diagnosed as autistic.

One of the most important advances in the field has been the growing recognition of a subgroup of autistic individuals who possess high verbal ability and develop a high degree of social awareness by utilizing an acquired, nonintuitive theory of mind. This variant of autism is called Asperger syndrome, and some individuals who exhibit it have successful academic careers in spite of their interpersonal communication problems, obsessive tendencies and restricted interests. Although autistic individuals with normal or higher IQs can show a high degree of social adaptation, even the most compensated have some difficulty in the give and take of everyday conversation and are unlikely to have intimate friends.

The theory of mind—that autistic individuals lack the ability to understand the role of mental states in others —proved to be a crucial step in explaining how the social and communication deficits of autism could coexist with good general abilities. This hypothesis also predicts that there is a specific substrate or pathway in the brain that gives us the ability to conceive of mental states, and recent brain imaging studies indicate that such an area may be located in the left medial prefrontal cortex. Yet the theory of mind is unable to account for all aspects of autism, such as stereotyped behavior and the desire for sameness or the exceptional talents present in a significant proportion of autistic individuals. Two additional hypotheses have been proposed.

FREEHAND DRAWING by E.C., a male autistic savant,
was made spontaneously and without any corrections.
Although the perspective appears realistic, it
is achieved without the “vanishing points” most artists
would need. Studies by Laurent Mottron and Sylvie
Belleville of the University of Montreal show that
E.C.’s ability to integrate parts of visual patterns is impaired;
he is unable to reproduce anything resembling
a human face but has exceptional ability to remember
and draw individual objects and geometric shapes.

Bruce F. Pennington of the University of Denver and others in the U.S., as well as James Russell and his colleagues at the University of Cambridge in the U.K., have put forward the executive dysfunction hypothesis, which proposes that autistic individuals have a deficit in executive functions such as planning and working memory, impulse control, and initiation and monitoring of action. The processing of executive functions is thought to occur in the prefrontal cortex, and poor performance of these functions is directly related to repetitive thought and stereotyped, rigid behavior in autistic individuals.

Francesca HappĂ© of London University and I have proposed the weak central coherence hypothesis as an explanation for the exceptional talents and restricted interests displayed by some autistic individuals. Weak central coherence refers to a preference by autistic individuals for segmental over holistic information processing. How the brain integrates information is obscure, but long-range connections between the hemispheres may well be involved. There is some evidence that people with autism process information in piecemeal fashion—the total attention of the autistic individual often is captured by fragments or selective features usually of little interest to normal persons. Surprisingly, autistic persons tend to be less susceptible to visual illusions, perhaps because they are less affected by the context in which the figure is embedded.

Because it provides a model for the ability to conceive of mental states, research into autism is stimulating philosophical debate on selfconsciousness. Future studies may lead to the identification of subcomponents or precursors of consciousness in other species, which in turn might lead to a better understanding of the development of conscious experience in humans.

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