Brain Bane

By Charles P. Alexander

The mysterious problem often surfaces in grade school: for no apparent reason, children have trouble reading. Though they may be intelligent and highly motivated, they still find it hard to distinguish between simple words like bat and pat. Sometimes the malady goes undiagnosed for years; but if the child is fortunate, a teacher or doctor will recognize the signs of a subtle disability called dyslexia, which may affect 10 million Americans.

In the 1970s scientists began to suspect that people with dyslexia have some fundamental problem with their vision or hearing, since children verbalize - words when learning to read. Studies have since suggested that victims have something amiss in the cerebral cortex, an all-important part of the brain responsible for thought and language. Last week researchers writing in the Proceedings of the National Academy of Sciences presented evidence that may pinpoint a spot in the cortex where dyslexia originates. It is an area of tissue called the medial geniculate nucleus (MGN), which affects hearing by acting as a relay station for auditory signals.

The researchers, led by Dr. Albert Galaburda of Harvard and Beth Israel Hospital in Boston, collected brains from dyslexics after the subjects had died, comparing these suspect brains with normal ones. Generally, they found, the neurons (nerve cells) in the MGN are the same size in both the right and left hemisphere of the brain. But in the dyslexia cases, notes team member Glenn Rosen, a Harvard neuroscientist, "we found that the size of the neurons is smaller in the left hemisphere than it is in the right hemisphere." The size differential is only 10% to 15%, but that may be enough to throw off the brain's timing and disrupt its crucial word-processing skills.

With reporting by Christine Gorman/New York