Inhibitory Mechanisms Underlying Vibrotactile Perception Appear Altered in Children with ASD

Background:  

Impaired responses to tactile stimulation are commonly reported in children with Autism Spectrum Disorder (ASD), and inabilities to habituate to sensory experiences and impairments in filtering (ir)-relevant sensory input have both been described. It has been hypothesised that disrupted neuronal inhibition underlies these sensory impairments and disrupted GABAergic function has been linked to autism. Recently we have shown that different aspects of tactile inhibitory function, including its role in habituation and filtering, can be probed using a battery of behavioral tasks. In this study we applied a battery of ten tasks to typically developing children (TDC) and children with ASD (ASD) to investigate the role of inhibition in the primary sensory cortex in different aspects of tactile processing in to investigate atypical touch sensitivity in ASD.

Objectives:  

Test whether TDC and ASD pediatric populations differ in their response to tactile stimuli, and whether this is specific to tasks probing mechanisms related to habituation and filtering.

Methods:  

Participants: 68 TDC and 32 children diagnosed with ASD (ages 8-12) participated (13F, 2 left-handed). Subject and parental consent was obtained under the approval of the IRB at Johns Hopkins University and the Kennedy Krieger Institute.

Design: All participants received a battery of vibrotactile tasks; (1) two reaction time tasks; (2) a static and dynamic (dynamic increase in amplitude) detection threshold (DT) task. (3) Two amplitude discrimination tasks (no adaptation, single site adaptation); (4) Sequential and simultaneous frequency discrimination; (5) Temporal Order Judgement (TOJ) with and without 25 Hz concurrent stimulation. All tasks used stepwise tracking and were preceded by three practice trials for training purposes.

Results:  

There were no differences in reaction time (RT) between the groups, although individual variability in RT was higher in ASD (p < 0.001). Dynamic DT was significantly higher than static DT in TDC (p < 0.008), but not in ASD, and static DT was higher in ASD than TDC (p < 0.005). Amplitude discrimination increased after single-site adaptation compared to baseline amplitude discrimination in the TDC group (p < 0.001), but not in the ASD group (p > 0.5), but the unadapted condition was significantly worse for ASD (p = 0.01). There were no significant differences in frequency discrimination or TOJ performance between the tasks and groups.

Conclusions:  

We have shown that children with ASD have different responses to vibrotactile stimulation than TDC. Differences in the effect of dynamic stimulation on detection threshold suggest impaired feed-forward inhibition in autism, which may reflect poor sensory filtering in autism. Higher baseline amplitude discrimination threshold in ASD compared to TDC, suggests that lateral inhibitory connections are weaker in ASD, and an absence of the effect of adaptation (as seen in TDC) suggests impaired modulation of lateral inhibitory connections in ASD, which may reflect aberrant habituation. Intact frequency and temporal order discrimination suggest intact temporal and synchronous processing in ASD. Understanding the specific mechanisms underlying sensory symptoms in autism may allow for more specific therapeutic or drug-targeting in the near future, that may alleviate these symptoms and improve quality-of-life.