Medicine: Scanning the Brain

Holly Jane Hyde, daughter of a Rhode Island chicken and apple farmer, had been a lively youngster and, with her brilliant coppery hair, was as bright as a new penny. But when, at seven, Holly went into second grade, she had trouble with reading. Then Holly's mother noticed that sometimes she seemed not to understand what was said to her; she gazed vacantly into space and occasionally picked up her luncheon sandwich and tossed it across the room for no evident reason.

At first the doctors could not be sure of the reason, either. It...