1.   And that is something that primate researchers are pursuing intensively, using PET scanners and other devices that can reveal brain activity during various mental tasks.

2.   PET scanners, electrophysiological recording, DNA analysis and other techniques are increasingly being used.

3.   PET scanners use short-living radioisotopes, injected intravenously, to see what parts of the brain are active during a task.

4.   There are now only about three dozen PET scanners in the United States.