Learning disabilities are very common. They (21) perhaps 10 percent of all children. Scientists now know there are many different kinds of learning disabilities and that they are (22) by many different things. There is no longer any (23) that all learning disabilities (24) differences in the way the brain is organized.
 Since there is no (25) sign of the disorder, some researchers began looking at the brain itself to learn what might be wrong.
 In one study, researchers (26) the brain of a learning-disabled person. They found two unusual things. One (27) cells in the left side of the brain, which control language. These cells (28) are white, in the learning disabled person, (29) , these cells were gray. The researchers also found that many of the nerve cells were not in a line the (30) they should have been. The nerve cells were mixed together.
 The study was carded out (31) the guidance of Norman Geschwind, an expert on learning disabilities. Doctor Geschwind (32) that learning disabilities resulted mainly from problems in the left side of the brain, and this part of brain failed to develop normally. Probably, he said, nerve cells there did not connect (33) they should. So the brain was like an electrical device in which the wires were (34) .
 Other researchers did not examine brain (35) Instead, they measured the brain’s electrical activity and made a map of the electrical (36) . Frank Duffy experimented with this (37) and found large differences in the brain activity of normal children and those with reading problems. The differences appeared (38) the brain. Doctor Duffy said his research is (39) that reading disabilities involve (40) to a wide area of the brain, not just the left side.

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