Compared to other areas of the brain, relatively little is known about cerebellar function (Kolb & Whishaw, 1990). A possible reason for this lack may be that damage to the cerebellum in adults rarely occurs without causing death.
Cerebellar abnormalities are far from rare in people with developmental disorders. Cerebellar abnormalities are highly associated with autism, spina bifida, Down syndrome, Williams syndrome, Joubert syndrome, and hydrocephalus (Leiner et al, 1991; Ziegler, 1990; & Bordarier & Aicardi, 1990). In the cases of spina bifida and hydrocephalus, it has become increasingly clear that the majority of individuals with the conditions are of normal intelligence (Amacher & Wellington, 1984). Recently, Ziegler et al called for a reappraisal of the intellectual abilities of individuals with Joubert syndrome, based on their success at unlocking an individual's potential through an augmentative communication system (1990).
It is known that the cerebellum plays an important role in regulating complex motor activities. Apparently cerebellar function is central to activities combining both motoric and cognitive components, such as writing and speech (Leiner et al, 1991). Interpretation of the difficulties individuals may exhibit with complex tasks may be difficult.
The cerebellum also plays an important role in maintaining homeostasis of the sympathetic and parasympathetic nervous systems. It is these systems that govern our "fight or flight" response. Levinson (1989) noted the association of anxiety to physiological symptoms relating to cerebellar-vestibular functions. The cerebellar-vestibular disturbances that he identified include: imbalance; dyscoordination; disturbances of muscle tone; impaired motion-processing; disturbances in orientation; triggering of per- severation mechanisms; and secondary destabilization of the auto- nomic nervous system. Clinical evidence related by Levinson demonstrates that anxiety levels affect the cerebellar-vestibular functioning of "normal" subjects. It would seem reasonable to assume that individuals with preexisting cerebellar-vestibular dysfunction are even more sensitive to the disruptive effects of anxiety.
As an occupational therapist once commented to me, virtually all of our ways of talking about anxiety, well-being, and security are phrased in terms of coordination and balance. Hence, we talk about "feeling off balance," "being on the edge," "on the brink." She maintained that we have evolved these ways of speaking about the state of anxiety and stress because we all experience impairment of those functions when feeling that way. Levinson's work seems to confirm this therapist's observations.
There is indeed support for this relationship in the literature. Individuals with Williams syndrome are described as having poor coordination and being prone to phobias, most often associated with height and uneven surfaces.(Arnold, Yule, & Martin, 1985).
Temple Grandin, an autistic woman, describes her lifelong struggle with anxiety in her autobiography, Emergence: Labeled Autistic.
There is evidence that attentional allocation and motor performance compete with each other. Brown & Donnenworth (1990) examined the performance of non-disabled individuals in handwriting tasks. As speed was emphasized, there was a commensurate decrease in accuracy. The reverse was also found to be true.
Case (1982) suggested a model of intellectual development that examines the role of increased efficiency across the developmental span. Her model describes the interactions of three components of performance. Storage space refers "to the hypothetical amount of space a subject has available for storing information." Operating space refers to " the hypothetical amount of space that a subject has for executing intellectual operations." Total processing space refers to "the subject's total central processing resources, that is, to the sum of his storage and operating space."
Case suggests that total processing space remains constant across the developmental period. She further suggests that "the developmental increase in short-term span results from a decrease in the amount of operating space required: as less space is required for operating, more becomes available for storage. She also proposes that " the amount of operating space which is required decreases as a result of an increase in operational efficiency."
Case was, of course, talking about normal development. It can be argued, however, that her model has significant implications for individuals with atypical neurological development. Such individuals can exhibit wide variations of competence across different situations (Rourke, 1988).
One way to think about this is to think back to the time when first learning to drive a car. This activity generally demands the total concentration of novice drivers. Even as ease increases on familiar roads, attentional demands sharply increase when a new driver hits an expressway for the first time. Anyone who has worked with a new driver has found that it is useless to give verbal directions all at once. Instead of saying "make you first right, your second left, and continue straight for two miles." One must give new drivers directions one step at a time, as the demands of driving get in the way of holding all that information and retrieving it in a timely manner. Of course, most of us become better at this as our confidence and proficiency increase over time.
Margaret Bauman, a leading researcher in neurological factors associated with autism, had some relevant comments regarding the neuromotor problems associated with autism. The following comments were made by her in the Spring, 1993 issue of the Advocate:
First, regarding dyspraxia in general:The current slew of "validation" studies depend on memory retrieval of stimuli such as pictures, and are far removed from the usual setting and style of everyday communication. Given the data gleaned from the observations of professionals such as Margaret Bauman and research regarding the complex interactions of neurology, situational variables, and affect, a number of factors need to be carefully examined in terms of "validation":"'Dyspraxia' means a partial loss of the ability to perform coordinated movements.Comments about dyspraxia and autism:
"In child neurology, the term 'dyspraxia' is frequently used to indicate that the child has difficulty learning a new motor skill, and/or performing a specific skill or task or task on demand.
"In practical terms, the dyspraxic child often has difficulty learning a new motor skill, such as pedaling a bicycle or tying shoes, skills which other children acquire with relative ease. Further, skill performance in the dyspraxic child is often less 'automatic' than for other children. The dyspraxic has to consciously think about what he is doing.""In regard to autism, many child neurologists, particularly those of us who see many autistic children in our practices, believe there is a high incidence of dyspraxia in this population.Regarding aphasia under stressful conditions:
"Some confusion may exist, however, because clearly many autistic individuals can perform certain motor activities very well.""Whether or not the autistic individual can become truly aphasic under stress remains an open question. Perhaps a more appropriate term would be 'dysphasic', which implies that the process is not a complete one and that while there may be difficulty in handling certain aspects of language, there is not a total absence of that ability. I agree with Doug that many autistic individuals seem to have difficulty producing in a demand situation, be it expressive language or some kind of motor task.
"My suspicion is, however, that the autistic person may have an exaggerated response to that type of situation because the stress of being observed has been added to a cognitive processing system which is already inefficient or somewhat dysfunctional in handling information."