Assessments of Stimulus Modulation in Autism

Background:

Adults with autism exhibit inhibitory deficits that are often manifested in behavioral excesses, such as repetitive behaviors, and/or sensory hyper-responsiveness. If such behaviors are the result of a generalized deficiency in inhibitory neurotransmission, then it stands to reason that deficits involving localized cortical-cortical interactions – such as in sensory discrimination tasks – could be detected and quantified. 

Objectives:

This study exemplifies a newly developed method for quantifying sensory testing metrics. Our novel sensory discrimination tests may provide (a) an effective means for biobehavioral assessment of deficits specific to autism and (b) an efficient and sensitive measure of change following treatment.

Methods:

The sensory discriminative capacity of subjects with autism (n=12, age range 16-40) and age matched controls (n=50) was compared for assessing the relationships between two nonstationary vibrotactile stimuli delivered to the glabrous skin. In one protocol, the intensity of the two stimuli were initially the same but were diverted at different rates and subjects assessed which of the two stimuli were more intense.  In a second protocol, the intensity of the two stimuli were initially very different, but were modulated until they were equal, and subjects indicated when the stimuli were first perceived to be equal.  A third protocol was used to obtain observations of the differences between static and dynamically modulated vibrotactile thresholds in each of the subjects.

Results:

Although the duration of modulation of the stimuli had a pronounced effect on the ability of the control subjects to either differentiate or match the stimuli, there was less of an effect on the observations obtained from the autism subjects.  However, comparison of the vibrotactile thresholds obtained using static vs. modulated stimuli revealed that the modulation of the stimulus had a much more pronounced impact on the thresholds of the autism group.

Conclusions:

The reduced impact of the duration of the modulated vibrotactile stimuli and the increased impact of the rate of change of the modulated vibrotactile stimuli on the responses of the subjects with autism was interpreted to be consistent with the reduced GABAergic mediated inhibition described in previous reports.  One significant aspect of this study is that the methods could prove to be a useful and efficient way to detect specific neural deficits in autism and perhaps monitor the efficacy of pharmacological or behavioral treatments.