The impact of stimulus properties on low- and high-frequency median nerve somatosensory evoked potentials.

Questioning whether stimulation properties in median nerve somatosensory evoked potentials show interactions multichannel recordings were performed in a three-factorial repeated measures design with the parameters (i) eyes opened versus eyes closed, (ii) stimulation intensity above motor threshold versus intensity sub motor threshold, (iii) stimulation rate 0.5 Hz versus 9 Hz resulting in somatosensory evoked potentials recorded during eight different conditions. Varying the stimulation intensity revealed an impact on the amplitude and the latency of the N20 source activity and on the amplitude, the duration and the number of peaks of the high frequency oscillatory (HFOs) sources. Modifying the stimulation rate lead to an effect on the amplitude and latency of the N20 and on the amplitude of the high-frequency oscillatory sources. The condition opened/closed eyes had an impact on the duration and number of high-frequency oscillatory. No relevant interactions between the stimulation properties were found. In consequence, varying one stimulus parameter already leads to a saturation of the low as well as high-frequency somatosensory evoked potentials components. Thus, the careful choice of stimulation parameters is a condition precedent for reasonable data interpretation.