5.2 Do organic influences play a role in autistic spectrum conditions?
Much of the evidence for organic influences, comes from subtle or non-specific types of dysfunction that may vary from one autistic individual to another. Steffenburg (1991) conducted a study of 52 children with ASDs. There was evidence for atypical functioning of the brain and/or nervous system in over 90 per cent of the participants, but in just under 50 per cent, these symptoms were non-specific. For instance, a substantial number of this latter group had epileptic symptoms and/or abnormal electro-encephalograms or EEGs. While deviations from characteristic EEG patterns usually reflect brain malfunction, they do not necessarily indicate what this malfunction is. Other individuals within this 50 per cent group showed atypical composition of the cerebro-spinal fluid (CSF), which circulates around the brain. Samples of CSF, which can be painlessly withdrawn by a small needle inserted into the spinal cord, contain breakdown products from neuro-transmitters, nerve cells and synapses. Atypical concentrations may indicate over-production of nerve cells and abnormal functioning of synapses. In a further 38 per cent of Steffenburg's cases, autism was accompanied by an additional organic or chromosomal syndrome known to involve brain damage. But in these cases it is not clear whether the brain damage is specifically linked with the autism or with the accompanying syndrome.
Other studies have attempted to investigate specific brain areas involved in autism. Some of the different brain areas suggested by these studies are shown in Figure 8 (a) and (b). Relevant findings are discussed here in Box 9 and later in Box 10.
Box 9: Major brain areas implicated in autism
Frontal lobes: Many researchers (e.g. Ozonoff, 1995) claim that autistic symptoms such as repetitive, inflexible behaviour and social inappropriateness resemble the behaviour of people who have suffered accidental frontal lobe lesions. The frontal lobes are thought to play a major role in executive function – planning or programming behaviour to achieve long-term goals. Patients with frontal lobe lesions lose the capacity to plan their behaviour; at times they seem impulsive or uninhibited, making irrelevant, inappropriate or thoughtless responses to a situation; at other times, they go on making the same response long after it has been proved ineffective. Evidence to support this frontal lobe link to autism comes from neuropsychological tests used in diagnosing frontal lobe lesions. Both frontal lobe patients and people with ASDs perform poorly on tests of flexibility in adopting new rules to solve problems. However there is no evidence of major frontal lobe lesions being implicated in autism.
Cerebellum: One set of studies using fMRI scans (e.g. Courchesne et al., 1988) reported underdevelopment within this area, which is known to play an important role in the control of motor movements, particularly those with a social function such as gestures, posture and expression. An abnormality in the cerebellum could play a role in the impoverished or idiosyncratic non-verbal communication usually associated with autism, but it is not clear how this explanation could be generalised to other symptoms. Ozonoff (1995) offers an alternative interpretation: since the cerebellum is one of several brain areas richly connected to the frontal lobes, primary damage to the cerebellum could be interrupting normal information flow to the frontal lobes, producing executive-type deficits as a ‘secondary’ effect.
Temporal lobes: Several PET scan studies suggest atypical functioning. The temporal lobes are the most common site for epileptic seizures associated with autism. They are known to play a crucial role in understanding language, a focus of core difficulties in autism, as well as in memory. Atypical functioning of the limbic system, internal to the temporal lobes, and especially the amygdala, which plays a key role in emotion, has also been implicated in autism (Baumann and Kemper, 1988).
Electro-encephalogram (EEG): Recording of the overall pattern of electrical activity in the brain, made by attaching electrodes superficially to the scalp. Sometimes used to identify brain dysfunction.
Chromosomal syndrome: Syndrome caused by chromosomal damage or anomaly. May comprise both psychological and physical symptoms.
Frontal lobes: Major area of the cerebral cortex, involved in a variety of cognitive function, particularly coordinating and planning behaviour.
Executive function: Programming or planning behaviour in order to meet particular goals. Frontal lobes are thought to play a major role in this.
Cerebellum: Brain structure located under the occipital lobes, involved in posture, movement and balance, and in information processing.
Temporal lobes: Major area of the cerebral cortex, involved in a variety of cognitive functions including understanding speech and memory.
Limbic system: Structures internal to the temporal lobes. Evolutionarily ‘early’ part of the brain that instigates ‘survival’ behaviours, including emotions and appetites, as well as relaying information to the cortex.
Amygdala: Small structure in limbic system of the brain. Particularly involved in emotion.