阅读理解 Learning disabilities are very common
They affect perhaps 10 percent of all children
Four times as many boys as girls have learning disabilities
Since about 1970,new research has helped brain scientists understand these problems better
Scientists now know there are many different kinds of learning disabilities and that they are caused by many different things
There is no longer any question that all learning disabilities result from differences in the way the brain is organized
You cannot look at a child and tell if he or she has a learning disability
There is no outward sign of the disorder
So some researchers began looking at the brain itself to learn what might be wrong
In one study,researchers examined the brain of a learning-disabled person ,who had died in an accident