Sensorimotor aspects and manual dexterity in autism spectrum disorders: A literature review

Objectives: Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by difficulties in communication and social interactions as well as by restricted and repetitive patterns of behavior and interests. They are frequently associated with motor signs. However, literature concerning these motor anomalies remains scarce when it comes to the adult population. Among motor aspects, those concerning manual motor skills warrant a particular attention as their alteration often persists through adulthood with a major impact on functioning and quality of life. The purpose of this article was to systematically review and analyze the literature on sensorimotor aspects and manual motor impairments in ASD. Methods: We have searched the Medline database using the Pubmed search engine and retaining all articles published since the year 2000 with either their title, abstract or key-words containing the root autis* and any combination of the following terms: hand, manual, finger, dexterity, prehension, grip or grasp. Reference lists where also reviewed. After irrelevant articles were excluded, 33 studies were retained for this work. Results: The basic motor anomaly in autism seems to be a deficit in sensorimotor integration. The central nervous system of individuals with ASD seems unable to efficiently extract sensory information and integrate it correctly into a motor plan and execution. This type of online correction aims to save time on the initial ballistic phase of a movement. Thus, its alteration results in generalized slowness and motor clumsiness that require retroactive feedback corrections. Moreover, difficulties in integrating external sensory information to correctly adapt movement to environmental requirements could explain stereotyped and inflexible behaviors characteristic of autism. The same sensorimotor alterations are found in both gross and fine manual dexterity tasks. They seem to persist significantly though adolescence and into adulthood. To explain these anomalies, the underlying neuroanatomical and neurofunctional substratum might be a hypoconnectivity within cortico-cerebellar tracts. However, several other cerebral structures are also implicated. A delay in the maturational processes of these structures appears to be the common determinant of motor signs found in ASD but also in neurodevelopmental disorders as a whole. Conclusions: Current works tackling motor aspects in autism comprise several limitations preventing homogenization of their findings. Firstly, characterization of the extremely diverse clinical forms of ASD does not always rely on the same clinical criteria or tools. Furthermore, the motor tasks and the clinical assessments used are not always the same across publications complicating comparison. Moreover, sample sizes are almost always small and only a few studies have addressed motor impairments in adults with ASD. Furthermore, only two studies examine the dynamic longitudinal evolution of motor aspects from childhood to adult age. Finally, despite a recent effort of a consistent number of publications converging towards the hypothesis of a deficit in sensorimotor integration, a common pathophysiological model explaining these deficits in ASD is lacking. A more precise description of these motor signs and further comprehension of the neurological mechanisms underpinning them would allow more tailored managements directed towards subgroups with more homogenous neurodevelopmental profiles.