Experienced clinicians often get their first diagnostic impression from observing their young patients’ initial social response, but also from looking at their odd posture or movements as they walk into the office. In his original paper, Kanner noticed several atypical aspects of his patients’ motor function such as their paucity of gestures, clumsiness, and, in some, delayed gross motor development. Though sparsely studied, motor impairments in individuals with Autism Spectrum Disorders (ASD) – autism for short – are frequent, with some studies reporting up to 80% of individuals having some type of motor deficit. Some of these, already identifiable during the crawling phase, are coming into focus in follow-up studies of the younger siblings of ASD children. Observations of gait abnormalities suggesting dysfunction of the basal ganglia go back to 1981 (Vilensky, Damasio, & Maurer, 1981). Motor abnormalities may interfere with adaptive functioning like dressing or writing, or the gestures that normally accompany and accent communication to emphasize its intent. With the exception of meaningless repetitive movements and gestures – stereotypies – motor abnormalities are categorized as “associated symptoms” of autism; thus they have not received nearly as much attention as social and language deficits, core criteria for an ASD diagnosis.
The unappreciated complexities of movement and posture make it challenging to define the motor deficits of children with ASD. Even such seemingly simple and overlearned movements as reaching for an object, walking while avoiding an obstacle, drawing, brushing teeth, or riding a bicycle involve complex sequences of motor commands that involve many interconnected parts of the brain. Before and during its execution, movement is inextricably linked to sensory information like vision and feedback from joints and muscles (proprioception, implicit awareness of body posture). In addition, it depends on intention, planning (executive function), and attention. There are mirror neurons in the brain that need to be activated for imitation and for many types of conscious and unconscious motor learning to occur.
Motor performance is observable clinically or on videos, and there are now advanced technologies to quantify its many aspects for scientific study, but these are only starting to be used in ASD. Genetic research is seeking reproducible behavioral or other characteristics to help make sense of the findings in genetic studies on chips which regularly reveal involvement of some genes with as yet unknown functions. Well defined motor abnormalities are strong candidates, among many others, to help define genetically meaningful clinical subtypes of ASD. Also, we know more about the brain pathways involved in the control of sensorimotor function than about those that underlie more complex abilities like sociability. These characteristics emphasize the need for advanced studies of sensorimotor function in autism.
Correlations of motor signs with anatomic MRI, especially the recently developed tensor imaging, show pathways between cortex and subcortical brain structures. Functional imaging reveals correlations between particular tasks’ activation of specific brain areas. Together they are starting to advance our understanding of some of the underlying brain bases of autism. Sadly, imaging in young anxious children with ASD is difficult unless they are sedated, which may be acceptable for ruling out a serious or treatable brain disease, but is not for research. Progress is being made toward shortening the procedure and making it more suitable for such children, rather than limiting it to the cooperative older children and adults with ASD who are the main subjects of current research.
Clinically-Defined Subtypes of Motor Findings in Children with Autism Spectrum Disorders
There are two main categories of movement, fine and gross, each of which engages sensory as well as motor brain networks. We emphasize that some individuals on the autism spectrum have no sensorimotor deficit, in fact that some are gifted, for example exhibiting extraordinary dexterity for spinning small tops, twirling strings, flicking a tiny piece of paper between their fingers, or swiftly and dexterously taking mechanical toys apart. Others show great agility at climbing on furniture or walking on edges while incapable of hopping on demand. We also emphasize that deficiency in one skill does not predict that others will also be deficient. The reasons for these puzzling differences remain explained.
Most purposeful movements require a lengthy apprenticeship (learning, praxis). Some of the deficits of fine motor abilities are impaired imitation and coordination (dyspraxia), writing (graphomotor deficits), gestures, and oro-motor control (speech articulation, feeding). Gross motor deficits involve the many aspects of gait and posture, including negotiating the physical environment. A recent clinical review of ASD children (Ming, Brimacombe, & Wagner, 2007) reports hypotonia in 51%, motor apraxia in 34% of the younger group, and intermittent toe-walking in 19%. Our laboratory found similar results in a prospective controlled study being prepared for publication.
Rogers and colleagues (Rogers, Hepburn, Stackhouse, & Wehner, 2003) found that imitation in children with ASD (mean age 34 months) was strongly correlated with joint attention and severity of autistic symptoms. The investigators suggested that difficulty imitating gestures may have more to do with generating or using internal sensory representations of movements than with understanding the meaning of gestures, because the children had more trouble copying postures and oral movements than manipulating objects.
Dyspraxia, often referred to as clumsiness, consists of difficulty learning a motor task despite the lack of demonstrable sensorimotor deficit. Clumsiness may be inappropriate as impaired gestures in ASD are not due to poor motor coordination. A comparison of children’s errors imitating movements, gesturing to command, and using tools suggests a generalized praxis deficit rather than a specific imitation deficit (Mostofsky et al., 2006). The investigators confirmed that on average children with ASD have poorer handwriting than age and IQ matched controls and that it involves letter formation specifically (Fuentes, Mostofsky, & Bastian, 2009), although large and sloppy handwriting might also reflect poor motivation or attention to the task.
We have devoted considerable effort to examining in detail video recorded motor stereotypies, defined as apparently purposeless repetitive movements. These often disrupting and stigmatizing behaviors may evolve into more serious self-injury or become maladaptive ways of avoiding tasks or social interactions. Based on the study of over 500 videotaped standardized play sessions, we have characterized and categorized motor stereotypies and examined their outcome in children with autism and other developmental disorders (Goldman et al., 2009). At preschool, stereotypies are linked to autism, as opposed to other developmental disorders, but by schoolage compromised nonverbal intelligence plays a crucial role in their persistence. We are currently evaluating whether there are particular stereotypies sufficiently characteristic of autism to serve as warning signals of the diagnosis and looking for brain correlates of stereotypies on MRIs.
Assessment of Motor Deficits
Clinical evaluation of motor function is a task for neurologists, developmental pediatricians, and physical and occupational therapists who may ponder whether they are seeing transient immaturity or evidence of a neurologically-based disorder. Worse, they are frequently unable to tell whether a child with ASD “couldn’t or wouldn’t do” a task like drawing a circle, throwing a ball, or hopping (Mandelbaum et al., 2006). Was it lack of cooperation, attention, imitation, or understanding of the commands that was at fault? Making naturalistic observations of the child during play or of spontaneous movements in other settings may help resolve the issue.
Standardized motor batteries are essential for research but do not explain the causes of failures. The Peabody Developmental Gross Motor Scale is most widely used for preschool children. Denckla’s timed tests of simple repetitive movements, the Physical and Neurological Examination for Subtle Signs (PANESS) (Denckla, 1974), apply to schoolage children and adolescents. These tests quantify motor deficits but are not specific markers for autism. Comparing preschool with autism and other developmental disorders, we determined that, in general, the neurologist’s clinical examination revealed that higher IQ rather than diagnosis determined better sensorimotor skills, except for stereotypies which were more prevalent in the autism group. Yet an attempt was made to differentiate high functioning autism from Asperger syndrome, a currently highly controversial issue, on the basis of quantitative kinematic analysis of targeted hand use (Rinehart et al., 2006). That study suggested that slower movements might characterize Asperger syndrome. Obviously, motor characteristics are but one potential screening approach for making this type of distinction.
Conclusion
Systematic study of sensorimotor function in autism is new. The focus of our laboratory and others has been to describe these deficits in children with ASD and other developmental disorders. In studies largely yet to be done, our goal is to understand their brain basis.
The main treatment for motor impairments in ASD is physical and occupational therapy, from which the majority of children clearly benefit. But we lack evidence on exactly what and how these therapies help and which child is most likely to benefit. Many studies have been published, but many had weaknesses. Some studies were short term, some enrolled single subjects or small groups, groups were not always well defined and homogeneous, and few used standardized measures to assess progress. Rare studies compared effectiveness among interventions in ASD compared to other developmental disorders, and few had sufficient power to evaluate the size of reported improvements and their effects on adaptive daily function.
The cost-effectiveness of all these expensive time-consuming interventions begs for more detailed assessment. More rigorous research on sensorimotor function in autism and better understanding of its neurologic basis are sorely needed. Various treatments are made available to children on the basis of diagnostic label rather than an analysis of the specificity of deficits to be remediated. The common goal of all professionals who care for individuals with ASD is to develop innovative, more effective, and less demanding and costly treatments than those currently available.
References
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