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Introduction

While fMRI can tell us whether or not a brain region is activated during a task, it
cannot tell us if that brain region is essential to the task or merely associated with it.
For instance, if a subject were to count while being scanned activity in visual cortex may
be observed from the subject visualizing the numbers. Unfortunately the only way to
determine if a brain area is essential for a given task is to deactivate that area and see if
that interferes with a subject's ability to perform the task. This is commonly done in
experiments with animals and with humans about to undergo cortical resection surgery
by using cortical cooling techniques or by applying electric current directly to the brain;
although for obvious reasons these methods can't be used on healthy human subjects
which are the focus of the bulk of our research. However, the cortex can be inductively
stimulated using eddy currents as a non-invasive way of suppressing cortical areas. This
can be accomplished by placing an inductive coil on the skull of a subject and applying a
high-current pulse to the coil (Barker, et al. 1985); the high ramp-rate of the pulse
creates a magnetic field around the coil which will in turn induce currents the cortical
tissue below the skull.

The use of this technique, called Transcranial Magnetic Stimulation (TMS) has
become a popular complement to fMRI, although currently fMRI and TMS experiments
must be run separately as fMRI compatible TMS systems are not yet available. This is
unfortunate because concurrent fMRI and TMS can provide a simple and verifiable way
to determine that the correct brain area was targeted by the TMS, as well the extent
and duration of suppression. So with this in mind we have adapted a commercially

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