Cuff-type pneumatic stimulator for studying somatosensory evoked responses with fMRI

For quantitative somatosensory testing in the clinical environment a microprocessor controlled MR-compatible stimulation device was developed. A main feature of this device is the use of an inflatable cuff allowing the application of defined test pressures (0-1000 mbar) to the skin surface. The cuff is pressurized by a piezoelectric proportional valve with embedded closed loop controller. The distortion of the pressure pulses, introduced by the tube between valve and cuff (tube lengths of 2 and 6 m), was evaluated. Two kinds of stimulation patterns were implemented by the microprocessor: constant frequency stimulation (selectable between 1 and 20 Hz) and stimulation with stepwise changing frequencies according to a pseudorandom sequence. Imaging tests (n = 8, index finger) showed more robust responses in S1 (contralateral) and S2 (bilaterally) if evoked by the random sequence. Both, the technical tests and the imaging results, demonstrate that this new stimulation system is well suited to set a standard for somatosensory stimulation in individual longitudinal studies or multicenter comparisons.