Description of potential curves

A clear N1 wave was apparent in the scalp waveforms at fronto-central locations (e.g., electrodes Cz, Fz, Fp1, Fp2) at both sessions in all subjects. The positive counterpart of N1 in lateral positions on the scalp was not present for activation of some electrodes in S2, S3 and S5. Figure 1 shows grand averaged evoked potentials recorded from electrodes Cz (central location) in response to activation of electrodes 3, 7, 11, and 15 in S4 the day following implant switch on and one month later.

Figure 1. Individual N1 responses at frontal electrode Cz in S4 at implant switch on and after one month of use for activation of electrode sites 3 (apical), 7, 11, and 15 (basal). Negativity is up. Blue: electrode 3, red: electrode 7, yellow: electrode 11, green: electrode 15.

Important inter-subject variability was observed in N1 latencies and amplitude. Latencies at Fz ranged from 72 ms to 119 ms at the first session and from 67 ms to 100 ms one month later. Amplitudes at Fz ranged from -4.9 µV to -0.5 µV at the first session and from -5.7 µV to -0.7 µV one month later. As it can be seen in Table 2, latencies of the N1 recorded at Fz tended to increase in S2, and decrease in S1 and S4, while its amplitude tended to increase in most subjects after one month of implant use except for S2 and S5.

Table 2. Latency and amplitude of the N1 component recorded at Fz for activation of each stimulation site at implant switch on and after one month of implant use for each subject.