The CTN function was tested by determining the threshold of EGM stimulation. The detailed method was described elsewhere.4-6,10 EGM thresholds were –6 (4 μA) to 34 dB (400 μA) in 2-dB increments. “No response” signified that the threshold was beyond the measurable range and was
statistically considered as 36 dB. EGM was performed every 3 to 7 days until 1 month after surgery and thereafter every 3 to 6 months until 12 to 24 months. EGM was performed by the specialist (Y.I.).