The Role of Chronic Neural Noise in Autism Spectrum Disorders

Background: Few theories of the neural basis of Autism Spectrum Disorders (ASDs) adequately address the well-known and oft-reported symptoms of hyper- and hypo-sensitivities in different sensory modalities (see Robertson & Simmons, this meeting). We argue that the existence of chronic levels of internally-generated neural noise in affective pathways might provide an explanation of these phenomena. To test this theory, it is necessary to directly measure perceptual abilities of ASD participants in “noisy” backgrounds. Whilst increased internal noise levels would normally mask a signal (and therefore increase thresholds), in some circumstances thresholds can be decreased (i.e. signals enhanced) via the well-known non-linear systems phenomenon of stochastic resonance. Objectives: To demonstrate the feasibility of chronic neural noise as a factor in ASD. Methods: We measured performance of adults with ASD and typical controls on a task involving a judgement based on visual motion information. The component motion trajectories of a cloud of moving dots were perturbed by increasing amounts of directional variation, and participants were asked to judge the overall direction of the cloud. Results: Peaks and troughs in performance of the ASD group, relative to the control group, as a function of increasing directional variation were suggestive of increased levels of internal noise in visual motion pathways. Conclusions: Taken together with other data from the literature on sensory processing within ASD (e.g. McKay et al, this meeting, in which point-light walkers were harder to detect on a background of noisy dots), these results suggest that increased levels of internal noise could be a factor in ASD. Furthermore, we suggest that these resonance and masking phenomena might underlie the sensory symptoms, and possibly other classes of symptom, within ASD.