Motor synergies: Evidence for a novel motor signature in autism spectrum disorder

In autism spectrum disorder (ASD), socio-communicative impairments and stereotypical behaviours are paralleled by sensorimotor deficits. Individuals with ASD show an altered selection of motor parameters, resulting in clumsy and fragmented actions. Here, we investigated inter-joint coordination and motor synergies as a potential substrate of motor control problems in ASD. Synergies enable co-controlling redundant motor degrees of freedom (DoF, e.g. joint angles, muscles) by mapping behavioural goals into a flexible and low-dimensional set of variables. This mechanism simplifies motor control and helps to find unambiguous solutions for motor tasks. In a reaching-grasping paradigm, children with ASD showed reduced coupling between DoF, which correlated with socio-communicative symptoms severity. Impaired synergies may help to frame well-established motor problems in ASD, including impaired motor sequencing and abnormal trial-to-trial motor variability. On the other hand, synergies also provide an effective and compact coding system of observed actions. Impaired synergies may thus jeopardize motor interaction by initiating bottom-up cascade effects, leading to pervasive impairments of social behaviour. Finally, we trained an automatic classification algorithm to distinguish between ASD and typically developing (TD) participants based on reaching-grasping kinematics. Classification accuracy reached up to 0.947. This result corroborates and expands previous accounts claiming that motor-based early recognition is feasible and effective in ASD.