By holding a magnetic coil over somebody's skull, a researcher can affect the activity of the piece of cortex beneath, while causing no pain to the subject.

ECONOMIST: The ethics of brain science

One new technique being used by some neuroeconomists is transcranial magnetic stimulation, in which a coil held next to the head issues a low-level magnetic pulse that temporarily disrupts activity in a certain part of the brain, to see if that changes the subject's preferences for example, for a particular food and how much he is willing to pay for it.

ECONOMIST: Neuroeconomics: Do economists need brains? | The

Instead, the coil is pulled through the external magnetic field, which induces a voltage across it.

ECONOMIST: Weighing a kilogram

The coil is suspended in an external magnetic field and the current running through it adjusted so that the attraction between the two magnets balances the gravitational force on the suspended mass.

ECONOMIST: Weighing a kilogram

That is because the transmitter uses a large flat coil, placed over the heart, to generate the magnetic field that powers the receiver.

ECONOMIST: Case history