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Brain Changes Tied to Over-Stimulation in Autism

Abundant, undersized cell columns could shed light on disorder

MONDAY, Feb. 11, 2002 (HealthDayNews) -- Structural differences in the brains of people with autism could help explain behaviors linked to this disorder.

Researchers suspect that abnormalities in cell mini-columns, which are functional groups of brain cells that process sensory information, may cause a chronic sensory over-stimulation for people with autism.

This flood of information triggers the disorder's characteristic withdrawal in an attempt to reduce the stimulation, according to the study.

The findings appear in the Feb. 11 issue of the journal Neurology.

Autism is a complex developmental disorder that interferes with the ability to communicate and interact socially. The symptoms of autism range from problems with verbal and non-verbal communication, repeated body movements and resistance to changes in routine, and even self-injurious behaviors.

More than 500,000 Americans have some kind of autism or other pervasive developmental disorder, a group of syndromes characterized by severe impairment in several developmental areas. Autism is four times more common in boys than in girls.

There is no known cure, but various therapies -- including early educational intervention -- have shown some effect.

A specific cause of autism has not been identified, but increasingly, evidence has suggested that differences in the brain may be responsible for the disorder. Recently, attention has shifted to cell mini-columns.

Lead author Dr. Manuel Casanova, a professor of neurology, anatomy and psychiatry at the Medical College of Georgia in Augusta, compares cell mini-columns to the silicon chip that controls a computer.

Mini-columns, which are found throughout the brain, are the brain structures that give humans our intelligence compared to other primates, he says. During development, cells migrate to the mini-columns and align themselves in rows.

Using medical imaging technology, the researchers compared five aspects of mini-columns in donated brain tissue of nine autistic patients and nine healthy people.

"That's where we found abnormalities," says Casanova. "We found that the brains of autistic individuals had too many mini-columns. Moreover, the mini-columns were smaller than normal."

"The mini-column is like a series of cells hung together like pearls on a string," Casanova adds. In a normal person, he adds, the brain region known as the thalamus would activate around 10 mini-columns. "In an autistic person, it could innervate 12 or maybe 14," he explains.

"It's a way for the thalamus to overpower the cortex," says Casanova. Computer modeling suggested that the increased number of small mini-columns provides autistic patients with too much stimulation from their environment.

Casanova compares this overflow of stimulation to trying to look directly at the sun. "For an autistic individual, if he or she looks at your face, it's like a flood of information," he says. "The only way that he or she has to react is by shying away."

Dr. Pasko Rakic, the chairman of neurobiology at Yale University, says that this research is interesting but needs to be confirmed in a larger study.

"If we are to understand this disease, which I understand has a genetic and developmental component, we have first to understand what is the biological basis of it," says Rakic.

Rakic says that the number of mini-columns is determined before roughly seven weeks of gestation, while the number of cells per column are added until up to 25 weeks of gestation. "However, maturation of cells continues after birth," he says.

"There are many [factors] that could disturb the formation of columns," says Rakic. "Some of these could be genetic, some could be environmental."

Alcohol and certain drugs are known to interfere with cell migration, he adds. "If we know that, then we'd better recognize that pregnant mothers should not take drugs of abuse or things of that sort."

Casanova says that the first three years of life provide a window for modifying brain circuitry to maximize a child's development. "We need to provide for diagnosis early on for early intervention," he says.

What to Do: For more information on autism, visit the Web sites for the Center for the Study of Autism, the Autism Society of America or the National Institute of Neurological Disorders and Stroke.

SOURCES: Interviews with Manuel F. Casanova, M.D., professor, Departments of Neurology, Psychiatry and Anatomy, Medical College of Georgia, Downtown Veterans Affairs Medical Center, Augusta; Pasko Rakic, M.D., Ph.D., professor and chairman, Department of Neurobiology, Yale University School of Medicine, New Haven, Conn.; Feb. 11, 2002, Neurology
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