11/26/2001

By TOM SIEGFRIED / The Dallas Morning News

SAN DIEGO – Everybody appreciates the diversity displayed by various human bodies.

Some bodies are good for basketball, some are best for ice skating, others are more suited for life as a couch potato. Nobody suggests that all bodies are equally equipped for any activity. But for some reason many people seem to think that brains should all be the same.

They aren't, of course. All are built from the same general blueprint. But hereditary differences in the construction materials and accidents along the way make individual brains develop in distinctly different ways. Sometimes the differences are unimportant; sometimes they cause behavioral problems or even severe psychiatric disorders. To understand such problems, it might be helpful to have an atlas of ordinary brain anatomy at different stages of development to see where some brain-building projects take a wrong turn.

Over the past decade, government researchers have been trying to make such maps. By scanning the brains of children and adolescents at two-year intervals, the researchers are able to illustrate the diverse ways that brains build themselves.

These studies so far have shown a lot of previously unsuspected nuances in brain development. For one thing, brain size differs enormously among normal individuals, even when taking height and weight into consideration.

"Brain size varies approximately the same way shoe size varies," says Judith Rapoport, a psychiatrist at the National Institute of Mental Health in Bethesda, Md., and one of the nation's leading researchers on childhood brain disorders.

Dr. Rapoport and her collaborators have discerned many other surprises while scrutinizing maps of the developing brain. For instance, brain development does not end in adolescence, as neuroscientists used to think. One important part of the brain, the cerebellum, does not reach its adult size until the mid-20s. And while most parts of the brain seem constrained in structure largely by genetics, the cerebellum appears to be far more susceptible to environmental influences during growth.

Other parts of the brain mature much sooner, but not all at once. The front and top parts of the brain seem to reach adult size by age 11; the sides don't achieve full growth until age 18. And some parts of the brain develop at different rates at different times. The corpus callosum, for example – a bundle of fibers connecting the brain's two halves – develops more rapidly at its front during a child's first years of life. Later on, it develops faster toward the back.

All these differences between normal brains are intriguing, but the real payoff in such studies is finding reasons why some brains go awry. Children with attention-deficit hyperactivity disorder, for example, typically have slightly smaller brains than their normal peers.

"In both males and females, there's a slight but significant difference in total" brain volume, Dr. Rapoport said in San Diego recently at the annual meeting of the Society for Neuroscience. "It is not accounted for by any differences in height or weight."

Genes must play a role in the brain-size deficit, because identical twins of hyperactive kids typically show a similar difference – even for a twin who doesn't exhibit hyperactive symptoms. Hyperactivity may be triggered by other events; in at least some cases, a specific brain injury (perhaps caused by a stroke before birth) may explain why one twin exhibits signs of the disorder and the other doesn't. In any event, the brain scans recorded by Dr. Rapoport and her colleagues clearly support the case that such behavioral problems are true biological diseases linked to defects in brain anatomy.

Of course, critics of modern psychiatric medicine sometimes contend that brain differences linked to these diseases may be caused by the medicine prescribed to treat them. But new findings, reported at the neuroscience meeting, argue otherwise.

Dr. Rapoport and colleagues have studied hyperactive youngsters who never received treatment and compared their brains with those of kids who had received medication over an eight-year period. The slightly smaller-than-normal brain size was found in both groups.

"It does appear that there's no evidence that stimulant drugs are the cause of these findings," Dr. Rapoport said at the meeting.

A similar study examined diminished amounts of gray matter in the brains of children with early-onset schizophrenia.

While schizophrenia usually strikes first in the late teens or early 20s, cases of childhood onset have been recorded. Many such cases, though, were misdiagnosed, so some children receive schizophrenia medication even though they don't really have the disease.

Again, a few critics claim that brain damage in schizophrenia patients is caused by treatment drugs. But brain scan comparisons show that the children accurately diagnosed with schizophrenia show a particular pattern of gray matter loss, beginning toward the back of the brain and moving toward the front region over a period of years. Misdiagnosed kids do not show that pattern of gray matter loss, even though both groups received the drugs.

In other words, brains can be different, some tragically so. Pretending they're not, or that medicines cause the differences, retards efforts to find ways of averting such tragedies.