Background

The speed with which an individual is able to make a simple motor response to a perceived stimulus may fairly be regarded as a significant index to his basic level of perceptual-motor integration. Developmental studies on reaction time in subjects with a neurotypical (NT) development report a decrease in simple reaction time (SRT) with increasing age and a strong correlation between upper and lower limb simple reaction time tasks. No studies are available in this regard in Autism Spectrum Disorder (ASD) subjects.

Objectives

The aims of this study are: 1) to assess developmental changes in the speed of a simple reaction at the lower and upper limb in ASD children as they age; 2) to assess the correlation between upper and lower limbs SRT in ASD children; 3) to assess the correlation between lower limb SRT and ankle dorsiflexors muscles strength in ASD children; 4) to compare the results with the same data obtained in a sample of 243 NT subjects. 

Methods

The study sample included 12 ASD subjects (10 males; age range 5 -18 years). The ASD subjects were diagnosed with autism according to the DSM V criteria, confirmed through ADOS-2 and under observation at our Institute. SRT was measured in milliseconds using a hand-held electronic timer and a light as the stimulus and finger or foot lever to trigger responses. The testing of ankle dorsiflexion force was done using a footplate attached to a spring gauge. All the tests employed have been validated for the study of sensorimotor components of balance into the Fall Screen Assessment System.

Results

At variance with NT group we found no significant correlation between both upper and lower SRT and age in ASD study group (upper limb: R Pearson=-0.056, p=0.863; lower limb: R Pearson=-0.065, p=0.841) and no correlation between lower limb SRT and ankle dorsiflexors muscles strength. Instead, similarly to NT group a significant positive correlation between upper and lower limb reaction time tasks was found (ASD: R Pearson=0.819, p=0.001; NT: R Pearson=0.666; p=0.000).

Conclusions

This is the first study that analyses upper and lower limbs SRT developmental variability and its correlation with ankle strength performance in ASD subjects. The absence of a developmental improvement in SRT and the impairment in lower limb SRT tasks found in ASD subjects point out a disorder of sensorimotor integration in ASD subjects potentially responsible for postural control imbalance.

Notes:

(1) School of Medicine and Surgery, University of Milan-Bicocca, Milano, Italy

(2) Autism Research Unit, Villa Santa Maria Foundation, Tavernerio, Italy