Characterization Of A Bimodal Electrocutaneous Stimulation Device

In order to improve observability of the processing of nociceptive and tactile stimuli, a new electrocutaneous stimulation electrode was developed. The electrode aims at combining the exact timing of electric stimulation with preferential activation of nociceptive or tactile afferents. The electrode is a compound electrode consisting of 5 needle electrodes for preferential stimulation of A delta (nociceptive) fibers and 4 flat electrodes for A beta (tactile) fiber stimulation. Stimuli applied with this "bimodal" electrode result in a sharp prickling sensation for the needles and a dull tactile sensation for the flat electrodes. The observed intensity of the stimuli is modulated by varying the number of applied stimulus pulses (NoP).In order to determine the effect of stimuli applied through the bimodal electrode on subjects, a characterization study was performed. The objectives were determining (1) sensation thresholds for both modes of the bimodal electrode, (2) subjective reports following stimulation with the two modes with different intensities and (3) Evoked Potentials (EPs) following these stimuli.11 subjects (9 male, 2 female) were recruited, each participated in two experiments. After sensation threshold determination, subjects were stimulated with a quasi random sequence of four stimuli (needle or flat electrodes with 1 or 5 pulses), each stimulus was applied 30 times. Subjects rated the perceived sensation on two Visual Analog Scales (VAS), one representing observed quality and one representing observed intensity. EPs were recorded per stimulus type.An electrode was developed which is capable of preferentially stimulating nociceptive and tactile afferents. The needle electrode sensation thresholds were lower than the flat electrode thresholds (0.72 +/- 0.42 (mean +/- SD) mA versus 3.1 +/- 1.2 mA). The subject averaged quality VAS score was significantly influenced by mode, the intensity score by NoP. The EPs were significantly influenced by both mode and NoP and suggest a difference in processing between the modes.