The name is absent

114

available TMS system, the Magstim Rapid (www.magstim.com) for use in an MRI
environment. To accomplish this we had to overcome two challenges, first the Magstim
Rapid is designed to be controlled manually by the experimenter (although it does
include features for rapid stimulation that make computer control possible), so we had
to devise a way to control the system using a computer so it could be synchronized with
fMRI experimental stimuli and the scanner. Second, both systems rely on magnetic
fields to operate, we therefore had to devise methods to prevent interference between
the TMS and fMRI.

AdaptingtheTMssystemforcomputercontroI

ControllingtheTMssystemthroughaParaIIeIPort

The Magstim Rapid is designed to be able to provide rapid trains of pulses of up
to 100Hz. Since it is impossible for a human to signal such a rapid sequence with button
presses, and since the TMS system does not have an internal sequence generator, the
system includes a port for external control to connect to a pulse train generator. We
were able to use this interface to provide the computer control necessary for syncing up
theTMSpulses, experimental stimuli, and fMRI scanner.

The software we use to run our fMRI experiments is Presentation
(www.neurobs.com). This software provides a large library of functions for delivering
visual and auditory stimuli, but is limited in its use of the parallel port; it can only control
pins 2-9 as outputs and pin 10 as an input. The TMS console uses a Centronics 36 port
for input control, and requires eleven lines of control for our purposes (Table 1 below).

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