Atypical Habituation of Early Brain Responses to Sensory Stimuli Predict Self-Reported Levels of Anxiety in Autism.

Background: An estimated 40-50% of autistic children, adolescents and adults suffer from clinically significant levels of anxiety that exacerbate core clinical characteristics and impact upon the quality of life of the individual and those caring for them. Recent studies suggest that the sensory processing differences that form part of the clinically defining characteristics of autism (ASD) play a significant role in the development and maintenance of anxious symptoms. Specifically, such sensory differences are thought to contribute to the heightened levels of Intolerance of Uncertainty that are consistently reported by autistic individuals and that constitute one of the proximal causes of anxiety in ASD.

Objectives: The current study further examines the role of sensory processing differences as a contributing factor to anxiety in autism by moving beyond mere self-report and examining basic brain mechanisms of sensory habituation through an auditory roving oddball paradigm.

Methods: 15 ASD and 13 age, and ability matched typical developing (TD) participants passively listened to a series of auditory tones whilst performing an unrelated change-detection visual task. The frequency of the tone changed pseudo-randomly following between 1 and 10 repetitions, and event-related potentials, time-locked to each tone, were monitored continuously using EEG (64-channels). Early (P50) and later (Mismatch negativity; MNN) markers of auditory processing were of most interest, which were derived by calculating the amplitude differences between ‘standard’ tones that had repeated at least 6 times and ‘deviant’ tones, which were the first tones in a new set. Participants also completed self-report measures of anxiety, sensory processing differences and intolerance of uncertainty.

Results: Groups differed in their early (P50) but not later (MNN) responses. Specifically, whilst P50 amplitudes to standards were attenuated compared to responses to deviants in the TD group (t = 2.10; df = 12; p = .057), no such difference was apparent in the ASD group (t = 0.53; df = 14; p = .60). Moreover, the extent to which P50 responses differentiated between standard and deviant tones correlated with self-reported levels of anxiety (r = -.40; p = .03), auditory hyper-sensitivity (r = -.42; p = .03) and intolerance of uncertainty (r = -.42; p = .03). More precisely, participants whose P50 differentiated more between standards and deviants reported lower levels of anxiety, sensory sensitivity and intolerance of uncertainty.

Conclusions: Our results provide further confirmation that sensory processing differences (in particular hypersensitivities) play an important role in the increased levels of anxiety that are reported by autistic individuals. Our observations suggest that abnormalities in very early sensory gating processes result in a lack of habituation to sensory signals in ASD, which leads autistic individuals to experience sensory signals as more intense than would typically be the case. In turn, the resulting hyper-sensitivity contributes to heightened levels of anxiety. Future studies will need to clarify how atypical sensory gating leads to increased levels of intolerance of uncertainty and why sensory gating processes are compromised in the first instance.