Autistic adults have unreliable neural responses

The top panel shows a map of the brain responses to the visual stimulation; they are similar across autism and control groups. 

The bottom left panel shows visual system responses of two individuals – one with autism and one control.

The average responses - across trials - are similar in terms of amplitude and shape, yet the trial-by-trial variability is much larger in the individual with autism (error bars are much larger). 

The bottom right panel shows that this is not a consequence of different head motion between the two individuals as both moved their head to a similar degree. 

Credit: Carnegie Mellon University 

Autism is a disorder well known for its complex changes in behavior—including repeating actions over and over and having difficulty with social interactions and language.

Current approaches to understanding what causes these atypical behaviours focus primarily on specific brain regions associated with these specific behaviours without necessarily linking back to fundamental properties of the brain's signaling abilities.

New research led by Carnegie Mellon University neuro-scientists takes the first step toward deciphering the connection between general brain function and the emergent behavioral patterns in autism.

Published in the journal Neuron, the study shows that autistic adults have unreliable neural sensory responses to visual, auditory and somatosensory, or touch, stimuli.

This poor response reliability appears to be a fundamental neural characteristic of autism. "Within the autism research community, most researchers are looking for the location in the brain where autism happens," said Ilan Dinstein, a postdoctoral researcher in Carnegie Mellon's Department of Psychology and lead author of the study.

"We're taking a different approach and thinking about how a general characteristic of the brain could be different in autism—and how that might lead to behavioural changes."

For the study, 14 adults with autism and 14 without—all between the ages of 19 and 39—completed sensory experiments while inside a functional magnetic resonance imaging (fMRI) machine located at CMU's Scientific Imaging and Brain Research center.

To test the visual system's neural response, participants were shown a pattern of moving dots. The auditory stimulation consisted of pure tones presented to both ears, and short air puffs were used to stimulate the somatosensory senses.

The fMRI measured each individual's brain activity during the experiments. In all of the primary cortices, visual, auditory and somatosensory, the within-individual response reliability was significantly lower—by 30-40 percent—in autism; meaning, there was not a typical, predictable response from trial to trial.

Thus, in the individuals with autism, there was significant intra-individual variability, with responses varying from strong to weak.

Non-autistic adults had replicable and consistent responses from trial to trial. "This suggests that there is something very fundamental that is altered in the cortical responses in individual's with autism," said Marlene Behrmann, professor of psychology at CMU and a leading expert on using brain imaging to understand autism.

"It also begins to build a bridge between the kind of genetic changes that might have given rise to autism in the first place—and the kind of changes in the brain that are responsible for autistic behavioral patterns.

More information: Dinstein et al.: "Unreliable evoked responses in autism." DOI:10.1016/j.neuron.2012.07.026