Autistic adults have unreliable neural sensory responses to visual, auditory, and touch stimuli, according to new research published in the journal Neuron.
This poor response reliability, the study's authors conclude, appears to be a fundamental neural characteristic of autism.
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"We are not suggesting that unreliable sensory - visual, auditory, touch - responses cause autism," cautioned NYU's David Heeger, a professor in the departments of psychology and neural science and one of the study's authors. "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 sub-serve those functions."
"Within the autism research community, most researchers are looking for the location in the brain where autism happens," said the study's lead author, Ilan Dinstein, who graduated from NYU's doctoral program in 2009 and is now a postdoctoral researcher in Carnegie Mellon's Department of Psychology. "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."
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 behaviors focus primarily on specific brain regions associated with these specific behaviors without necessarily linking back to fundamental properties of the brain's signaling abilities.
The research published in Neuron takes a significant step toward deciphering the connection between general brain function and the emergent behavioral patterns in autism.
The researchers studied 14 adults with autism and 14 without -between the ages of 19 and 39 -by conducting sensory experiments inside a functional magnetic resonance imaging (fMRI) machine at CMU's Scientific Imaging and Brain Research Center. To measure visual activity in the brain, 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.
The within-individual response reliability was significantly lower - by 30-40 percent - in autism. This was the case for all three sensory systems: visual, auditory, and somatosensory (i.e., touch). This meant 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.
"And, what I think is so powerful is that we sampled visual, auditory and somatosensory senses. We were unbelievably thorough and attacked every sensory modality and showed the same pattern of unreliability across all three senses."
The study also presents the first time that researchers have investigated 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 observed. "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."
The study also included researchers from the Department of Neurology at the University of Pittsburgh and Israel's Weizmann Institute of Science.
The Simons Foundation, Pennsylvania Department of Health and the National Institute of Health and National Institute of Child and Human Development's Autism Center of Excellence at the University of Pittsburgh funded this research.
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