Treating the brain with magnets went mainstream a few years ago,
when the technique proved successful at relieving major
depression. Now the procedure, repetitive transcranial magnetic
stimulation (rTMS), shows promise for another mysterious, hard-
to-treat disorder: chronic pain. Until now, pain seemed out of
reach for rTMS because the regions involved in pain perception
lie very deep within the brain. The other disorders helped by
rTMS all involve brain areas close to the skull. To treat
depression, for example, a single magnetic coil directs a
magnetic field at the dorsolateral prefrontal cortex, a region
of the brain's outer folds. When aimed at different areas of
these outer folds, rTMS improves the motor symptoms of
Parkinson's disease, staves off the damage of stroke, lessens
the discomfort that follows nerve injury and treats obsessive-
compulsive disorder. The magnetic field affects the electrical
signaling used by neurons to communicate, but how exactly it
improves symptoms is unclear—scientists suspe