Stability and Reliability of Detection Thresholds for Human A-Beta and A-Delta Sensory Afferents Determined by Cutaneous Electrical Stimulation

Schematic of left arm marked by five equi-spaced sites. Sites 2 and 4 lie over the a) ulnar and b) median nerves, respectively.

Experiment I. Effect of pulse duration on detection threshold and pain threshold. A: Sensory thresholds at three different pulse durations. The solid points represent the mean PT's; the hollow points represent the mean DT's. Detection threshold error bars are too small to be visible. B: Ratios of pain to detection thresholds at three different pulse durations. Each data point represents the mean (± standard error) PT:DT ratio for the 10 subjects.

Experiment II. Time course of detection and pain thresholds for each site averaged over the 10 subjects. Each series of connected data points represents 6 successive determinations approximately 5 minutes apart of DT and PT, without moving the electrode. Z1 through Z5 correspond to sites 1–5 in Figure 1.

Pain/Detection (PT:DT) ratios for all trials in Experiment II plotted against detection threshold. Data from each subject are shown by a unique symbol. Each subject received 6 DT and PT trials at each of 5 locations for a total of 30 trials for each of the 10 subjects. The line indicates the maximum possible ratio with a stimulation limit of 10 mA. Data from 3 subjects with both detection thresholds greater than 8 and ratios near the limit are classified as outliers.

Experiment III. Effect of site on detection threshold and pain threshold. A: Sensory thresholds at the 5 sites (depicted in Figure 1). The hollow points represent mean DT's; the solid points represent mean PT's. B: Ratios of pain to detection thresholds at the 5 sites. Each data point represents the mean PT:DT ratio for each individual subject.

Pain/Detection (PT:DT) ratios for all trials in Experiment III plotted against detection threshold. Data from each subject are shown by a unique symbol. Each subject received 6 DT and PT trials at each of 5 locations for a total of 30 trials for each of the 10 subjects. The line indicates the maximum possible ratio with a stimulation limit of 10 mA. Data from 3 subjects with both detection thresholds greater than 0.8 mA and ratios near the limit are classified as outliers.