Disruption to Motor Intentions in Children with Autism: Evidence for Brainstem Timing Errors

Background:

Human movements are prospective. They must anticipate ahead of time their lawful consequences. In children with autism, evidence indicates a common disruption to movement may underpin its early pathogenesis (Trevarthen & Delafield-Butt, 2013). and may be a cardinal feature (Fournier et al., 2006). Yet, more work is required to better characterize this possible ‘autism motor signature’ and to probe its neurodevelopmental origins. In this study, we employed smart tablet computers with touch-sensitive screens and embedded inertial movement sensors to ecologically record the subsecond motor kinematics of movements made by children developing with and without autism.

Objectives:

(1) Characterise the subsecond motor kinematics of children with autism and those developing typically to identify autism-specific features. (2) Probe likely neurobiological origins of the motor disruption based on these variables.

Methods:

37 children 3-6 years old diagnosed with Childhood Autism and 45 age- gender-matched children developing typically were included. Children with sensory or motor impairment were excluded. iPad mini tablet computers employed two education games: (1) ‘Sharing’ where the main gameplay was to divide a piece of food and distribute it among four children; and (2) Creativity where gameplay was open, unstructured colouring of a toy or animal. Data were collected from the tablets' inertial sensors (tri-axial accelerometer, tri-axial gyroscope and magnetometer) and touch screen. Raw values and simple kinematic calculations produced 262 features. Previously we analysed these using machine learning methods with a classification accuracy of 93% (Anzulewicz, Sobota & Delafield-Butt, 2016). Here, these features were extracted and analysed using standard statistical multivariate analyses to identify significant ones. Further, kinematic analyses of goal-directed gestures were analysed using standard biomechanical methods, and groups compared.

Results:

Features associated with impact force made at initial contact and forces put into the device during a gesture were significantly different between groups. Gesture kinematics were faster and larger across both games, with more distal use of space in children with autism. Children with autism made faster taps on the screen. Greater peak velocities with commensurate increases in acceleration and deceleration peaks and with significantly increased jerk amplitude were evident in goal-directed movements in the autism group.

Conclusions:

These data indicate under- and over-exertion of the motor impulse with velocity remaining high at a movement’s conclusion. Acceleration-deceleration shifts with increased jerk amplitude appeared to oscillate at a fast, subsecond rate of ca. 13 Hz, corroborated by others (Cook et al., 2013). Greater impact forces confirm a greater velocity at movement termination, a finding in agreement with others’ (Crippa et al., 2015). Disruption to sub-second control of intentional movements and timing their termination are two key features of the autism motor signature. A likely neuromotor origin of these is the brainstem inferior olivary pace-maker responsible for action timing. Disruption to basic action patterning will thwart motor intentions regularly, and may lead to distress, withdrawal, and the familiar simplification found in repetitive movement.