Acoustic Startle Response in Children with Autism Spectrum Disorder with and without Co-Morbitiy of Attention Deficit Hyperactivity Disorder

Background: Parents of children with Autism Spectrum Disorder (ASD) and or Attention Deficit Hyperactivity Disorder (ADHD) often report that their children have trouble “tuning out” sensory stimuli. It is estimated that over 96% of children with ASD have difficulties filtering sensory information. Typically, no objective physiological measures of sensory filtering are assessed for those with ASD nor for those with ADHD and clinicians must rely on subjective reports of behaviours and symptoms. Though many symptoms overlap between ASD and ADHD and some estimates of comorbidity are as high as 50%, there is evidence that the underlying causes of these conditions may differ. An objective method for assessing sensory filtering ability is to study the eye-blink component of the startle reflex (SR) in response to unexpected startling sounds. The subject’s ability to habituate to these random noises can be quantified and compared to traditional diagnostic tools.

Objectives: This study sought to quantify the differences and similarities in sensory filtering among individuals with ASD, ADHD, both ASD and ADHD (Dual), and those with neither ASD nor ADHD (Control). A second objective was to compare EMG SR data to current clinical measures of sensory-related behaviours currently.

Methods: Data from 32 participants aged 9-17 years were grouped according to diagnostic status into one of the four groups mentioned above. All individuals were assessed using pencil and paper standardized tests for characteristics of ASD, ADHD as well as the Raven’s Progressive Matrices as a measure of non-verbal intelligence. Orbicularis occuli electromyograph (EMG) measurements were recorded during an acoustic startle protocol that included input/output function, and habituation. Baseline EMG SR amplitude, and response latency were compared between groups. Welch’s Anova and Games-Howell post-hoc analysis was conducted to determine statistical significance of findings.

Results: Baseline average EMG voltage of participants with ADHD was significantly higher than the baseline voltage for those with ASD or those who were dually diagnosed (p<0.05). The ASD group’s average amplitude of startle response was significantly higher than Controls and included a period of sensitization. The degree of habituation over the course of the session was not strongly correlated to the subjective reporting measures of ASD nor ADHD symptoms nor did it correlate strongly to age, or IQ. No differences between groups was seen for the latency of the startle response. Latency was not effected by the age of the participant.

Conclusions: The results of this work demonstrate that there are differences between the population of individuals who have ASD with ADHD and those that have ASD without ADHD. The correspondence of the EMG data to subjective measures indicates limitations in relying on third-party subjective assessments for diagnostic purposes. The EMG SR of the groups will inform the validity of animal models of autism currently being used in basic research and further develop the neuroscience models of sensory filtering pathways.