Approximately 1.5 million children and adults in the U.S. have autism and it is estimated to be the fastest growing developmental disability with a 10 - 17 percent increase each year. While much is known about the symptoms of autism, the exact cause of the condition is not yet defined.
A new model of the brain developed by Dr. Stephen Grossberg, professor and chairman of the Department of Cognitive and Neural Systems at Boston University, and Dr. Don Seidman, a pediatrician with the DuPage Medical Group in Elmhurst, IL, sheds light on the triggers of behaviors commonly associated with autism. The paper, "Neural Dynamics of Autistic Behaviors: Cognitive, Emotional, and Timing Substrates," appears in the July issue of the journal Psychological Review, published by the American Psychological Association.
"Autism involves multiple genes and correspondingly, people with autism are known to have multiple cognitive, emotional, and motor symptoms - such as impaired development of speech and difficulty expressing emotions," said Dr. Grossberg. "The iSTART model describes the various brain mechanisms that underlie autism and how they may give rise to the symptoms of the condition."
iSTART, which stands for Imbalanced Spectrally Timed Adaptive Resonance Theory, is derived from the earlier START model developed by Grossberg to explain how the brain controls normal behaviors. The new model describes how brain mechanisms that control normal emotional, timing, and motor processes may become imbalanced and lead to symptoms of autism. START and its imbalanced version iSTART are a combination of three models, each one of which tries to explain fundamental issues about human learning and behavior.
The first, called Adaptive Resonance Theory, or ART, proposes how the brain learns to recognize objects and events. Recognition is accomplished through interactions between perceptually-driven inputs and learned expectations. Inputs attempt to match expectations which helps prompt the brain to anticipate input/expectation patterns.
"When a match occurs, the system locks into a resonant state that drives how we learn to recognize things; hence the term adaptive resonance," explained Grossberg.
The degree of match that is required for resonance to occur is set by a vigilance parameter which controls whether a particular learned representation will be concrete or abstract. Low vigilance allows for learning of broad abstract recognition categories, such as a category that is activated by any face; high vigilance forces the learning of specific concrete categories, such as a category that is activated by a particular view of a familiar friend's face. iSTART proposes that individuals with autism have their vigilance fixed at such a high setting that their learned representations are very concrete, or hyperspecific.
"Hypervigilance leads to hyperspecific learning which perpetuates a multitude of problems with learning, cognition, and attention," said Grossberg.
The second model, called the Cognitive-Emotional-Motor, or CogEM, model, extends ART to the learning of cognitive-emotional associations, or associations that link objects and events in the world to feelings and emotions that give these objects and events value. Under normal circumstances, arousal of the circuits in the brain that control emotion are set at an intermediate level. Either under-arousal or over-arousal of these circuits can cause abnormal emotional reactions and problems with cognitive-emotional learning.