New techniques yield insights on autism
Studies indicate that the number of diagnosed cases of Autism, or autistic spectrum disorder, is increasing with around 0.6% of the population affected. Early infantile autism was first described almost 60 years ago and autism has been the subject of intense research activities ever since, however the origin of the condition is still not understood. This review issue of Philosophical Transactions B, a Royal Society publication, provides a comprehensive overview of the latest research on autism and highlights some new techniques that will progress future understanding.
“All the papers in this review present something new: either new techniques that will yield positive results for future studies or consolidation of current knowledge that will enable the subject to move on,” says Prof. Uta Frith of University College London, coeditor of the issue with her colleague Dr. Elisabeth Hill.
New studies of the brain
The study of brain development in autism is new and facts are emerging which challenge older theories. One of the more established ideas is that damage in the amygdala, part of the social brain, is central to the disorder. Salmond et al have found in their structural anatomical studies using magnetic resonance imaging (MRI) that only half of the cases they examined had amygdala damage. MRI images were analysed using individual voxel-based morphometry – a technique that allows comparison of aspects of brain structure independent of brain size by assessing the density of grey and white matter in the brain. Other structures in the brain, including the orbitofrontal cortex, cerebellum and superior temporal gyrus, were more consistently associated with autism leading to the hope that this new technique will prove to be an invaluable research tool in the future. Supporting behavioural studies using the startle response, thought to reflect amygdala function, showed no difference between the study and a control group.
The fusiform face area of the brain is involved in the processing and discrimination of faces. Schultz et al use MRI techniques to show that it is also engaged in general social processing and is part of a set of well-established brain regions (including the amygdala) specific to social cognition. Their main finding is that the extent of brain activity in the fusiform face region is related to the accuracy with which social tasks are performed.
The signs and symptoms of autism are still puzzling. Since a biological basis of autism was accepted, approaches from developmental cognitive neuroscience have been applied to further our understanding of the autism spectrum. One of the puzzles presented by ‘autism’ is that the communication issues common to all patients can coexist with high intelligence, for example Asperger syndrome. Asperger Syndrome has readily established itself as a household name but its diagnosis is still controversial. Hippler and Klicpera revisited the original records from Asperger’s clinic and thus provide a unique documentation of the historical origins of the condition.
The huge variety of the autism spectrum makes sub-grouping based on behaviour and neurological causes attractive. Tager-Flusberg and Joseph have used new sensitive neuropsychological techniques to establish such subgroups. In particular groups can be identified by large discrepancies between verbal and non-verbal IQ. In cases with good verbal IQ autism tended to be milder, whereas cases with good non-verbal IQ showed more severe autism and were also characterised by larger head size. Larger head size in autism is a recent finding and correlates with brain size and weight, indicating potential physiological differences between subgroups.
Two papers by Charman and Swettenham respectively investigate a particularly early and striking symptom of autism namely lack of joint attention. This symptom proves highly predictive of later social impairment, but is not due to an absence of the normal ‘reflex’ to follow eye gaze. Hobson and Bishop studied the social interactions of congenitally blind children and relate them to features in autistic children.
Klin et al have used a new ‘eye-tracking’ technique to investigate how autistic individuals extract meaning from normal social scenes and showed that their viewing patterns are dramatically different from normal.
Three main neuro-cognitive theories of autism have emerged over the recent past – theory of mind deficit, weak central coherence, and executive dysfunction – with such cognitive explanations of the core features of autism providing a vital interface between brain and behaviour.
Baron-Cohen et al analyse groups of adults by means of questionnaires and derive two quotients: Systemising and Empathising. Successful social interaction requires a need to empathise and this is contrasted by the ability to systemise – a drive to analyse and construct systems. Results show a distinct male / female difference (males favour systemising; females prefer empathising) but also that individuals with autism show an unusually strong drive to systemise.
The preoccupation with detail and an inability to “see the wood for the trees” lies at the heart of the weak central coherence theory. Work by Plaisted et al develops this theory and shows new dissociations between the components of perceptual processing in autism.
Booth et al look at a possible link between weak central coherence and executive dysfunction by comparing boys with autism to boys affected by attention deficit hyperactivity disorder (ADHD) using drawing tasks. Both groups show planning impairment but only the autistic boys show a detail-focussed drawing style.
Individuals with autism show problems with motor coordination. The extent of such difficulties in the autistic population is not known, but the work by Mari et al indicates differences in movement planning and execution for autistic children. The observed movement abnormalities, which show striking parallels with Parkinsonism, provide evidence that they may play an intrinsic role in abnormal neurophysiological processes in at least a subgroup of individuals with autism.
Window on the mind
Autism is a neuro-developmental disorder that allows a unique window on the relationship between mind and brain. Autism is characterised by impaired social interaction and communication as well as repetitive behaviours and restricted interests. The consequences of this disorder for everyday life adaptation are extremely variable.
“New ideas are coming forward that link mental dysfunctions with brain abnormalities, many being facilitated by the use of new techniques,” concludes Prof. Frith. “We now know more about the brain basis of autism and the nature and variability of its behavioural symptoms. We are more aware of early signs of autism and the persistent difficulties experienced by well-compensated adults. And we are starting to seriously recognise and examine the unique cognitive strengths of many individuals with autism.”
Contact for further information
For more details of the papers (copies of the full papers and contact details of authors) or to arrange interviews with issue editors Prof. Uta Frith and Dr. Elisabeth Hill, please contact:
Copies of these papers can be accessed on the Royal Society Publications website (http://www.pubs.royalsoc.ac.uk) via the FirstCite website. Username and Password for this site can be supplied on request from Tim Reynolds. Copies of the papers and Introduction are also available as Word documents.
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