"Imagine you have the experience that your world is completely unreliable," said New York University psychologist David Heeger. "Every time you look at something it looks slightly different, or every time you hear something you hear it slightly differently."
That's what the environment may be like for people with autism, based on a study that he and researchers in Pittsburgh and Israel published today in the journal Neuron.
The study found that the brains of people with autism responded erratically to sights, sounds and touch, compared with those of typical people.
That might make the world a scary place for those on the autism spectrum, speculated Mr. Heeger and Marlene Behrmann, an autism expert at Carnegie Mellon University, and that might help explain such autistic behaviors as repetitive motions and the urge to learn detailed information about narrow topics.
In the study, 14 high-functioning adults with autism and 14 people without the disorder did a task while lying in a magnetic resonance imaging machine. As they stared at a computer screen, they saw patterns of dots, heard a series of beeps and felt puffs of air on their hands. The scientists then watched how their brains responded to the simple stimuli.
The typical people had fairly predictable brain responses to the sensory signals, but the people with autism were all over the lot, Ms. Behrmann said. Some of them reacted strongly to the sounds but weakly to the dots, while others had erratic reactions to the same stimulus from one trial to another.
The variations in the autistic people's brains may help explain why some people with the disorder are hypersensitive to noises or touch, or have trouble with balance and gait, she said, and also may be one reason that people with autism are more likely to have epilepsy.
More broadly, it could be what underlies the repetitive motions that some children with autism make, or the fixation some of them have on developing expertise on such narrow topics as types of trains or baseball statistics, she and Mr. Heeger said.
If an autistic child's environment seems unpredictable, Mr. Heeger said, "one way to deal with that is you might repeat an activity that you can do over and over, and that might be comforting."
Children who flap their hands or spin a plate also seem to get lost in the activity, and "so that kind of closing in, which is seen as a primary symptom of autism, may actually be a secondary outcome of a compensatory mechanism."
In the same way, Mr. Heeger said, higher functioning children with autism may be "drawn to a learning style where they learn a lot of details that are very closely associated with each other and they end up knowing an enormous amount of detail about a very narrow topic, and that too could be a compensating strategy for controlling this unreliable brain response."
Both Ms. Behrmann and Mr. Heeger stressed that they are speculating about the link between these behaviors and the brain imaging results they saw in the new study, and hope to design further experiments to test their hypothesis.
Besides CMU and NYU, the study involved researchers from the University of Pittsburgh and the Weizmann Institute of Science in Rehovot, Israel.
As the subjects in the scanner watched the dots, heard the beeps or felt the puffs of air, the researchers looked specifically at the parts of their brains that initially process that information, known as the "primary cortex."
Seeing erratic responses in the primary cortex could be a sign that other parts of the brain are dysfunctional, too, Ms. Behrmann said. "If you can see changes at the front door, it's not surprising you would see changes downstream."
Genetic studies of people with autism show that many of the abnormal genes may involve the synapses -- the basic connections in the brain that transmit information between neurons.
"The idea we have," Mr. Heeger said, "is that these disruptions in the way that synapses work in the brain can lead to disruptions in neural circuits, and that may lead us toward a fundamental core principle that will help us understand the full spectrum of autism disorders."
Mark Roth: firstname.lastname@example.org or 412-263-1130.