They were placed on the thyrohyoid membrane between the hyoid bone and the thyroid cartilage at the entrance location of the ISLN into the larynx on both sides.
Thus, after the termination of ISLN stimulation via electrodes, the 2 active electrodes were once again placed on the thyroid lamina (the nearest place to the vocal cords and the recurrent nerve) and the previous current was repeated precisely.
Figure 1 demonstrates mean F0, maximum (max) F0, and minimum (min) F0 for the rest and SES periods related to ISLN electrode placement.
The SD F0 means of the rest and SES durations related to electrode placement on the ISLN are shown in figure 2.
Table 1 demonstrates jitter, shimmer, HNR, mean intensity, maximum intensity, and minimum intensity results related to electrode placement on the ISLN. As the table presents, the means of rest compared to those of the SES period for both jitter and shimmer increased: The changes in the means were 0.09 and 0.9, respectively, which were statistically significant (jitter: P<0.001 and shimmer: P<0.001).
The present study examined the possibility of imposing changes on the vocal cords via SES on ISLN topical location on skin.
Nonetheless, our findings demonstrated that it was possible through the stimulation of the vocal cords directly via the ISLN.
As a result, heightening of aperiodicity can be concluded consequent to electrical stimulation on the ISLN. Gorham-Rowan et al.
(20) stimulated the ISLN by inserting needle electrodes around the ISLN for normal awake participants and reported voice break during phonation in 1 of their 3 subjects.
(22) Stimulation of the deeply placed nerves (such as the ISLN) will, therefore, be feasible.
The other reasons include different methods in electrode placement, different stimulated organs (internal laryngeal muscles versus ISLN in our study), different sizes of electrodes, and dissimilar time of recording voice (after or during SES presentation, as was the case in the present study).
This finding confirms the notion that by dispossessing and excluding the ISLN from the SES-affected area and also by delivering the current at the nearest place to the vocal cords and the recurrent nerve, SES cannot stimulate the vocal cords or the recurrent nerve.