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Children with autism often focus intently on a single activity or feature of their environment. New research might help to explain this behavioral trend, providing evidence that the brains of young people with autism are slower to integrate input coming from more than one sense at the same time.
During study of the disorder decades ago, research into these basic tendencies was common. But in subsequent years, scientists have tended to focus more on complex issues, ranging from communication troubles to underlying genetic patterns.
Recently, however, more studies have set their sights back on some of the simple processes that most people take for granted, such as sensory intake, as a way to better understand more high-level manifestations, such as social interaction issues. "We believe that these things interact in very significant ways," says Sophie Molholm, an associate professor of neuroscience at Albert Einstein College of Medicine and co-author of a new study about multi-sensory processing.
The research, published online August 19 in Autism Research, used electroencephalograms (EEGs) to measure electrical activity in the brain through the scalp of subjects as they encountered various stimuli. Seventeen children (ages six to 16 years) with autism—and 17 age- and IQ-matched normally developing kids—watched a silent video of their choice throughout the testing. Meanwhile, tones and vibrations were administered in random order, sometimes separately, sometimes at the same time. The EEG readings were time-stamped to the stimuli and compared across all of the children to assess brain activity trends during single- and multi-sensory stimulation. Although the video presented visual stimuli, Molholm points out that because it was a consistent exposure throughout the experiments and the EEG readings were set to pick up on the sound and somatosensory stimuli and averaged out over so many tests, it becomes akin to "background brain activity that will sum to zero," she notes. "It's really just something to keep them busy."
A simple stimulus takes about 20 milliseconds to arrive in the brain. When information from multiple senses registers at the same time, integration takes about 100 to 200 milliseconds in normally developing children. But those with autism took an average of 310 milliseconds to integrate the noise and vibration when they occurred together.
This difference, "at one level, is a very minor time delay," Molholm says. "But if you're thinking about human cognition…that could really interfere with normal processing," making what she describes as a "pretty significant impact." The research team also found that shortly after a stimulus was presented, brain activity in which timing seemed similar in typically developing children and in those with autism, the children with autism had lower overall signal strength, signified by lower amplitude waves on the EEG.
Although the study cannot definitively explain any direct behavioral correlates, it might hint at some of the underlying reasons for many of the disorder's hallmarks, such as sensitivity to excessive sensory stimulation.
"Maybe part of the reason these children might want to block out this—what seems to them extraneous stimulation—[is that] it fails to gain meaning for them as it does for other people," Molholm notes. She and her colleagues made clear in their study that these children were still eventually able to integrate the inputs from multiple senses and that there is a chance that as they become older, the children's integration speed could increase. The researchers proposed that one reason for this consistent delay is that children with autism might need to direct their attention to stimuli to achieve integration, whereas most others are capable of doing it implicitly.
Although the EEG is able to detect brain activity location and timing on a relatively minute scale, it does not paint a complete picture of the physiology behind these observed delays. "This is just a small step to understand multi-sensory integration," Molholm says. "Part of what we'd like to do next is look at brain anatomy and possibly how connectivity between different functional regions differs in autism."
Pinning down more data about how children with autism respond to multi-sensory stimuli should also help researchers, therapists and parents to evaluate sensory-integration therapy, which has been a popular treatment for individuals with autism. At present, "there's no objective measure to know if your sensory-integration therapy has worked," Molholm notes.
Empirical EEG maps might also eventually become a component of a more precise diagnostic toolbox, Molholm says. "We'd certainly like that to be the case," she says. And the EEG-stimulus test has the advantage of being "a passive paradigm," in which children do not have to execute tasks or take many directions, thus allowing most all developmental levels and a wide range of ages to undergo parallel analysis.