Low Sensory Reliability In Autism

Background: Several prominent theories of autism including the “enhanced perceptual functioning” (Mottron 2001), “weak central coherence” (Frith 1995), and “intense world” (Markram 2007) theories suggest that autism is characterized by sensory abnormalities, which are intimately related to the “core” social/cognitive symptoms of autism. Yet there is remarkably little examination of the integrity of sensory cortices in autism with which to support or refute these hypotheses. In the current study, we use functional neuroimaging to focus on a basic neural response characteristic – reliability. ‘Reliability’ here refers to the “within-subject” consistency of neural responses across multiple trials. Reduced sensory reliability may cause the world to be perceived as a confusing inconsistent environment and, thereby, be related to the manifestation of autistic behavioral symptoms.

Objectives: To compare the reliability of basic visual, auditory, and somatosensory neural responses across individuals with autism and age-, gender-, and IQ-matched typical adults. We hypothesized that decreased neural reliability may be evident in multiple sensory systems of individuals with autism.

Methods: We used functional magnetic resonance imaging (fMRI) to measure response reliability in a group of high functioning adult individuals with autism and matched typical controls.  All subjects were presented with the same stimulus in multiple trials and the response variability was estimated across trials. The visual stimulus contained visual motion (coherently moving dots), the auditory stimulus contained pure tones, and the somatosensory stimulus contained air puffs to the hand. Subjects performed an unrelated orthogonal visual task (rapid letter detection) to control attention throughout all of the experiments.

Results: Individuals with autism exhibited equivalent response amplitudes, on average, to those of matched controls, in all three modalities yet showed significantly reduced response reliability (larger between trial variability). This result was evident to different extents in the three sensory modalities tested.

Conclusions: This is the first study to compare responses in three sensory modalities between individuals with autism and matched typical controls. The results show normal/equivalent response amplitudes, on average, in all sensory areas rather than hypersensitive responses as predicted by the “intense world” theory (Markram 2007). However, response reliability was reduced in all of the sensory areas examined, suggesting that individuals with autism may be perceiving an “inconsistent world”. Individuals with autism exhibited abnormal neural responses at the earliest stages of sensory processing in response to “basic” stimuli, which have little social or cognitive value. This suggests that autism might be characterized by widespread neural abnormalities rather than selective abnormalities limited to cognitive, social, and/or emotional brain areas. Whether these abnormal neural characteristics of sensory cortices are related to the triad of behaviors that characterize autism, remains to be determined.