24-channel transcutaneous electrical sensory stimulation of the forearm: Effects on cognitive performance and autonomic arousal compared with single-electrode stimulation

Figures & data

Figure 1. Anatomical placement of cathode and anode electrodes.

Notes: Schematic showing placement of 24 cathode electrodes in four columns on the volar and dorsal surfaces of the left forearm. (Bottom) Photograph of placement of the 20-mm diameter (~3.14 cm²) cathodal electrodes 1–12 (Columns 1 and 2) on the volar surface of the left forearm. The large 51 × 102 mm (~52 cm²) rectangular anodal electrode can be seen between the body of the left biceps and triceps, as can the ShefStim breakout box (top right of photograph). During actual stimulation a cohesive bandage was wrapped around the forearm to secure the cathode electrodes in position.

Table 1. Mean “first felt” absolute and relative current intensities

	Distal forearm		Mid-forearm		Proximal forearm
	Medial-volar surface of left forearm
Electrode number	1	2	3	4	5	6
Intensity (mA)	3.2	3.0	2.7	2.2	1.9	1.7
Relative to E13	80%	75%	67.5%	55%	47.5%	42.5%
	Lateral-volar surface of left forearm
Electrode number	7	8	9	10	11	12
Intensity (mA)	2.4	2.4	2.8	2.2	1.9	1.9
Relative to E13	60%	60%	70%	55%	47.5%	47.5%
	Lateral-dorsal surface of left forearm
Electrode number	13	14	15	16	17	18
Intensity (mA)	4.0	2.7	2.6	2.7	3.0	2.9
Relative to E13	100%	67.5%	65%	67.5%	75%	72.5%
	Medial-dorsal surface of left forearm
Electrode number	19	20	21	22	23	24
Intensity (mA)	3.6	2.9	2.5	2.2	2.5	2.5
Relative to E13	90%	72.5%	62.5%	55%	62.5%	62.5%

Notes:

See Figure 1 (top) for numbered electrode placement. Mean (n = 10 participants) individual electrode current intensities (mA) are shown, and these are also expressed as a percentage, relative to the area with the greatest “first felt” current (middle of dorsal wrist surface; distal end of extensor pollicis longus muscle; electrode 13 [E13], Figure 1, top). These relative intensities, were used when establishing individual participants’ “strong but comfortable” current levels and during TESS delivery.

Figure 2. Effect of TESS pattern on two-point discrimination scores.

Notes: Mean two point discrimination total errors stratified by TESS pattern. Error bars show +/−2 standard errors. A significant between-pattern difference in task performance was seen with the single electrode stimulation condition (electrode 1, Figure 1) resulting in an increased number of errors (p = 0.023 post hoc Fisher LSD test; multivariate ANOVA).

Figure 3. Mean integrated-SCR (μS) across eight, 1-min epochs, for all tasks, stratified by TESS pattern.

Notes: All tasks collapsed. (Top middle) Stroop. (Top right) Tangram puzzles. (Bottom left) letter search. (Bottom middle) spot the difference. (Bottom right) two-point discrimination. A significant main effect of time is seen during all TESS patterns and during all tasks (except during spot the difference, where a new set of picture-pairs was presented every two minutes). There was no significant between TESS pattern effect on integrated-SCR on any of the tasks.