Objective: This paper describes the development of ultra-high frequency transcranial magnetic stimulators for biphasic and polyphasic quadripulse stimulation (QPS) of the human cortex in order to investigate neural plasticity. QPS originally describes a set of four monophasic stimuli with an inter-stimulus-interval (ISI) in the range of 1.5 to 100 ms, typically repeated every five seconds. Besides QPS, the described devices are able to set a quadripulse at much higher repetition rates (IBIs down to 200 ms) enabling quadri-Theta-Burst-Stimulation (qTBS). Methods: Insulated gate bipolar transistors (IGBT) were used as high voltage/high speed switch to control the current flowing through the stimulation coil. Biphasic and the polyphasic stimuli were applied over the human primary motor cortex (M1-HAND) to elicit motor evoked potentials (MEP). Technically parameters of the devices were determined and applicability for qTBS proto-cols is derived. Results: We built two devices, which allow the application of quadripulses with biphasic and polyphasic pulse currents, respectively. ISI as short as 1.0 ms with a IBI down to 200 ms is possible. In addition the devices allow to apply user defined protocols enabling individualized treatment. Conclusion: The biphasic as well as the polyphasic qTBS device is able to clearly elicit MEPs and is strong enough to apply qTBS protocols to subjects. Significance: This paper describes a novel topology of a stimulation device, which enables QPS and qTBS with biphasic or polyphasic pulse shapes at ultra-high frequencies. This enables research on protocols that can modulate cortico-spinal excitability within short stimulation times.      «

Objective: This paper describes the development of ultra-high frequency transcranial magnetic stimulators for biphasic and polyphasic quadripulse stimulation (QPS) of the human cortex in order to investigate neural plasticity. QPS originally describes a set of four monophasic stimuli with an inter-stimulus-interval (ISI) in the range of 1.5 to 100 ms, typically repeated every five seconds. Besides QPS, the described devices are able to set a quadripulse at much higher repetition rates (IBI...     »