Page 225 - Handbook of Biomechatronics

Fig. 23 Stability and selectivity of the FINE electrode. Stability and selectivity of
implanted cuff electrodes. (A) We implanted three cuffs with a total of 20 channels
in the forearm of subject 1: a four-contact spiral cuff on the radial nerve of the forearm
and an eight contact FINE on the median and ulnar nerves. The electrode leads ran sub-
cutaneously to the upper arm and connected to open-helix percutaneous leads via
spring-and-pin connectors (27–29). A universal external control unit (UECU, Ardiem
Medical) supplied single-channel, charge-balanced, monopolar nerve stimulation.
(B) Sensation locations after threshold stimulation at week 3 post-op. Cuff electrodes
were highly selective, with each contact producing either a unique location or unique
sensation. Here, the letter represents the nerve and the number represents the stimulus
channel within the nerve cuff around that nerve. Thus, M3 is the third stimulus channel
within the median nerve cuff. Ulnar (U) locations presented the most overlap at thresh-
old, but differentiated in area expansion at suprathreshold responses. The subjects drew
the borders around areas of perception. Areas outside the template, for example, M3,
represent a small wrap-around of sensation on the digit. (C) Repeated weekly over-
lapping threshold locations of channels M2, M3, M4, M5, and M8 for weeks 3 through
10 post-op indicated consistent location perception. Locations remained stable for all
stimulation waveforms used. (D) Mean normalized threshold charge density for all chan-
nels on the median (blue), ulnar (green), and radial (red) cuffs of subject 1 shown as a
solid line. Shaded areas indicate the 95% confidence interval. An unbiased, stepwise
search determined the threshold. Frequency was a constant 20Hz. During weeks
2–8, percept thresholds for subject 1 were 95.5 42.5nC (n¼59), 70.7 59.2nC
(n¼50), and 40.7 12.4nC (n¼24) for the median, ulnar, and radial nerves, respectively.
Linear regression of the threshold stimulation intensity for perception over 8weeks for
every channel was unchanging [18/19, analysis of variance (ANOVA) test, P 0.067] or
decreasing (1/19, ANOVA, P¼.044). Subject 2 was also stable (P .087) with thresholds
of 141 46nC and 95 47nC for the median and radial nerves, respectively.
(E) Threshold tracking of median channels M3, M4, and M5 to 68weeks and thereafter
showed no significant change in threshold over time (P¼.053, .587, and .773, respec-
tively). (From Tan, D.W., Schiefer, M.A., Keith, M.W., Anderson, J.R., Tyler, J., Tyler, D.J., 2014.
A neural interface provides long-term stable natural touch perception. Sci. Transl. Med. 6
(257), 257ra138. https://doi.org/10.1126/scitranslmed.3008669.)