A new study, published in the journalNeuron, reveals that autistic adults have unreliable neural sensory responses to visual, auditory and somatosensory (touch) stimuli.
This poor response appears to be a basic characteristic of autism.
Up until now research on what causes atypical behaviors in autism has focused primarily on specific brain regions without necessarily tracing back to the brain’s fundamental signaling abilities.
Now, neuroscientists at Carnegie Mellon University have taken the first steps toward deciphering the connection between general brain function and behavioral patterns in autism.
“Within the autism research community, most researchers are looking for the location in the brain where autism happens,” said Ilan Dinstein, Ph.D., 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 behavioral changes.”
For the study, researchers recruited 14 adults with autism and 14 without, all between the ages of 19 and 39. The volunteers participated in sensory experiments while inside a functional magnetic resonance imaging (fMRI) machine.
For visual stimulation, participants were shown a pattern of moving dots. Pure tones were presented to both ears for auditory stimulation, and short air puffs were used to stimulate the somato-sensory senses. The fMRI measured each individual’s brain activity during the experiments.
Non-autistic adults had replicable and consistent responses from trial to trial. However, in those with autism, the within-individual response reliability was much lower (30-40 percent); meaning there was not a typical, predictable response from trial to trial. Responses varied from strong to weak.
“This suggests that there is something very fundamental that is altered in the cortical responses in individual’s with autism,” said Marlene Behrmann, Ph.D., professor of psychology at CMU and an 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.
“And, what I think is so powerful is that we sampled visual, auditory and somato-sensory senses. We were unbelievably thorough and attacked every sensory modality and showed the same pattern of unreliability across all three senses.”
The study was also the first to investigate multiple sensory systems, at a primary brain function level, within the same autistic individual.
“One of the problems with autism is that there is considerable variability in symptoms across individuals,” Dinstein said. “In this case, we have a tremendous amount of data on each individual and each of their three sensory systems. And, we see the same unreliability across all of them in autism relative to the controls.”
Although the study focused on adults, the team plans on continuing the research to further investigate how the details of sensory unreliability play out in younger autistic groups.
“We are not suggesting that unreliable sensory — visual, auditory, touch — responses cause autism,” said David Heeger, Ph.D., professor of psychology and neural science at New York University.
“But rather that autism might be a consequence of unreliable activity throughout the brain during development. We’ve measured it in sensory areas of the brain but we hypothesize that the same kind of unreliability might be what’s limiting the development of social and language abilities in the brain areas that serve those functions.”