‘All humans are sacred, whatever their culture, race or religion, whatever their capacities or incapacities, and whatever their strengths or weaknesses might be’. (Jean Vanier, founder of L’Arche).
The single deficit model of autism is, in our opinion at the Minded Institute, doing people diagnosed with autism and their families a gross dis-service. Autism is complex and multi-faceted and, as yet, is not attributable to any specific physiological pathology. We have been searching for biomarkers for autism for some time now. We are still searching. We shall look in this blog post at arguments for and against the notion that autism can be characterised by a specific deficit.
Arguments For a Specific Deficit
One approach used to study autism has been the neuropsychological approach, in which the brain is characterised it terms of a normal brain with some modules impaired. One model, which comes from the neuropsychology tradition, is the single cognitive deficit model which traces autism to a single underlying cognitive deficit. Within this approach, autism has been viewed as caused by impairments to specific modules; some researchers have argued that autism, for example, is due to a deficit in a module that handles ‘Theory of Mind’ (TOM) computations. The central understanding is that only one module is damaged, resulting in a specific cognitive deficit, known as a ‘pure case’. However, ‘pure’ cases are in fact extremely untypical and the notion of a ‘pure’ case assumes that modules pre-exist. A non-modular architecture can produce an apparently ‘pure’ case, however, and the argument, therefore, rapidly falls apart. Furthermore, even the few ‘pure’ cases that have been documented would reveal subtle secondary deficits once more dynamic hypotheses have been considered.
From the recent evidence, therefore, the neuropsychological approach falls short of explaining the so-termed deficits underlying autism and does not fit in with recent developments in developmental neurobiology. Recent findings suggest that brain development turns out to be highly plastic across the life span as opposed to being comprised of static modules as the neuropsychological approach suggests. In addition, another recognised complication for single cognitive deficit models is the possibility of cognitive subtypes, which has been discussed for some time in the case of autism.
From Single Deficit to Multiple Deficit Explanations.
The Diagnostic and Statistical Manual for Mental Disorders , which includes criteria for autism, has taken a phenomenological, categorical approach. This suggests that all defined ‘disorders’ are heterogeneous and cannot therefore be defined by a single deficit. The diagnostic criteria for autism, for example, accepts that children are affected in multiple domains of function due to both biological and environmental factors, which modify the risk for aberrant pathways during brain development.
Another approach for understanding autism is the causal model. This attributes the ‘deficits’ found to three main arenas, namely biological, cognitive and behavioural.
It is increasingly accepted that autism is a complex disorder that is unlikely to have a single cause. It is, however, in many ways more complex than many mental health and development disorder presentations on account of the triad of impairments first defined by Wing (1980) – impairments of reciprocal social interaction, communication and imagination – each potentially requiring a causal theory of their own. The most convincing evidence for a genetic disposition comes from studying close relatives of those with autism, with twin-studies being particularly informative. Concordance has been found with over 60% of monozygotic twins, whilst there was no concordance found with dizygotic twins. Whilst the particular genes involved are not yet known, a strong candidate is a locus on chromosome 15q.
It has also been reported that close relatives of those with autism have an elevated frequency of Aspergers and schizo-affective anxiety disorders. It would, therefore, follow that the genetic risk factors for autism may extend to other, distinct brain conditions. Furthermore and interestingly, far more boys are affected than girls; one study puts the estimate at 3.8:1. This could be argued, however, not to be a genetic phenomenon, but rather that the male brain is more susceptible than the female brain. Indeed, recent research by Janet Treasure at the Maudsley has suggested that this is indeed the case, with anorexia argued to manifest in girls as a form of autism. The diversity of the gene mutations identified in autism point to the conclusion that there is no single ‘autism gene’, with the rising prevalence suggesting an environmental factor. Current thinking hypothesizes that there needs to be genetic susceptibility, which could extend across multiple genes, and exposure to environmental factors in order for autism to develop. Potential environmental factors have been suggested including nutrition, living in towns as opposed to rural areas, drugs used in pregnancy, and heavy metal toxicity amongst others.
In addition to biological and environmental factors, cognitive factors also come into play in the conundrum of autism. Structural abnormalities in the limbic system are seen in people with autism for example. Studies have found there to be disturbances of memory function, alongside deficits in attention and cognitive flexibility, both attributable to the hippocampus. In addition, mood disorders such as anxiety often accompany autism, with 84% of children with autism meeting the criteria for an anxiety disorder in one study. Such anxiety is also attributed with hippocampal and amygdale function, as is the desire for routine found in many people with this diagnosis. Another well-documented trait of autism, namely the perception of facial emotion, has been suspected to involve the hippocampus, amygdale and overlying cortex, with social interaction known to be adversely affected by hippocampal lesions. The ‘chicken or the egg’ question, however, remains. Are the anomalies in brain structure a pre-curser to autism or do the behaviours exhibited by the child with autism alter the brain structure? Whilst the jury is still very much out on this, it is interesting to note that in more than 90% of cases, there is no medical explanation for the autism present.
It would appear, therefore, that multiple biological and environmental factors modify the risk for autistic behaviour, but, and most importantly, this risk is further moderated by measurable environmental factors (leading to self-accommodation). We therefore seem to have a circle of inter-related factors wherein it is impossible to determine what exactly causes which deficit and what exactly is a marker for which behaviour. Thus, biological markers, coupled with environmental factors can feed into cognitive abnormalities and behavioural presentations, which are then moderated by environmental factors and so on. Deficits themselves arise from each of these levels, not only in autism but also in other developmental disorders and mental health presentations.
Associations between deficits in autism are extremely difficult to interpret because they could reflect bottom-up influences (stemming from the ‘innate’ deficit) on high-level processes, top-down influences (reversing or altering the ‘innate’ deficit) on low-level processes or the deficits could be causally connected. When we consider the difficulty in isolating the ‘innate’ deficits, the ability to interpret associations becomes close to impossible.
The notion of a person with autism having a normal brain with certain modules impaired simply fails to take into account the plethora of inter-related factors which cause the varying phenotype of each person with this diagnosis. Thankfully, researchers such as Karmiloff-Smith are taking away the very legs such reductionist beliefs are standing on. Whilst further research is certainly needed into each of the factors present, implications for treatment can already be drawn. A multi-modal, multi-disciplinary approach, as suggested by Reiss, would appear to be the way forward, with seemingly separate disciplines such as neuroscience, psychiatry, psychology etc. accepting and embracing the wisdom and potential contributions that could be made by the other. Further research would, therefore, draw on methods from multiple disciplines and include extensive inter-disciplinary dialogue. The multiple benefits of yoga for people with autism would also, one would hope, form part of this discussion.