Sensitivity was 20 μV/div (digit–wrist) and 50 μV/div (palm–wrist), low-frequency filter was 2 Hz, high-frequency filter was 10 kHz, duration of pulse was 0.1 ms, and rate of pulse was approximately 1/s. Sweep speed and the machine used were not specified.

This study was performed in the supine position.

Following the antidromic method [1], signals were recorded using surface ring electrodes placed distally to the digits from the proximal stimulation of the median nerve (S) on the palm and at the wrist. Sensory nerve action potentials (SNAPs) were recorded from digit I (thumb), digit II (index), digit III (middle), and digit IV (ring). Active ring (A) electrode was placed on the proximal interphalangeal joint of digit I, digit II, digit III, and digit IV; the reference ring (R) electrode was placed on the distal (R) interphalangeal joint of the same digits. Each wrist–digit recording was made separately, at a 14 cm distance between the recording and the stimulating electrodes which was used for each wrist–finger test (Figs. 1, 2, 3, and 4). To study the palm–digit segment, the authors performed stimulation on the palm recording SNAPs using ring electrodes from digit II and digit III (Figs. 5 and 6). Ground (G) electrode position was not mentioned in the text; the figures show the ground electrode positioned on the palm.

Stimulations were applied to the median nerve proximal to the distal wrist crease and on the palm. For wrist stimulation (S), the median nerve was stimulated on a surface point between the tendons of the flexor carpi radialis and the palmaris longus muscles (ideally proximal to the distal wrist crease). Wrist stimulation was made at a fixed 14 cm distance from the active ring (A) recording electrode placed distally to the digit. For palm stimulation (S), the median nerve was stimulated at a fixed 8 cm distance for both palm–digit II and palm–digit III segments. The interelectrode distance between the cathode (−) and anode (+) of the stimulating electrodes was 3 cm. The authors did not specify if surface disk electrodes (the same used for wrist recordings) or a handheld bipolar stimulator was used for palm stimulation.

Onset latency (ms) was measured from the onset of the stimulus to the onset of the negative deflection of the evoked sensory nerve action potential (SNAP); peak latency (ms) was measured from the onset of the stimulus to the negative peak of the wave. The negative peak amplitude (μV) was measured from the stimulus artifact to the peak of the negative deflection of the SNAP; peak to peak amplitude was measured from the negative to the positive deflection of the wave. Durations (ms) were recorded from onset of the negative deflection to its return to the baseline and from the onset of the negative wave to the positive peak. To establish the antidromic conduction in the palm–wrist segment, the latency value was taken from the latency measured from the wrist to finger. Temperatures were monitored at the point of stimulation and at the point of recording. All tests were performed with stable temperatures ranging from 31 to 33 °C (the majority were 32 °C), when necessary the limb was warmed with an infrared lamp. Normal values were obtained from 30 median nerves of 30 healthy subjects (age range 22–58 years, mean age 37.8 years). The side to side latency difference was analyzed from 15 subjects who were tested bilaterally.