Time-windowed block for unmyelinated fibers in the sciatic nerve of the frog

An artificial sensation can be produced in neuroprotheses by functional electrical stimulation of the sensory fibers in the peripheral nerves. The stimulation amplitude has effects on the perceptive field and the sensation modality. Increase beyond a certain threshold causes annoying sensations such as itch and pain. In this thesis, a novel method is proposed to improve this problem by blocking these unwanted sensations. In this study, a DC hyperpolarizing stimulation with a subsequent exponential decay was employed to block the conduction of C fibers of the frog's sciatic nerve. The block was applied in a time window to allow the propagation in myelinated fibers. The neural activity was measured by CAPs. For the blocking stimulus, two delays (4, 6 ms), three durations (4, 6, 8 ms), and five amplitude levels relative to the excitation threshold of C fibers were used. The excitation characteristics were also measured. In the CAP traces, the C component was reduced in 44% of the valid trials (n=67). The valid trials were the recordings in which the blocking stimulation did not evoke activity in myelinated fibers. After aligned-rank transform, 2-way ANOVA was performed to test the effects of block duration and amplitude on the reduction of C components. There were no significant effect of block duration (p=0.87) and amplitude (p=0.12). There was also no significant interaction between block duration and amplitude. Data from all trials (n=292) were included in Pearson correlation analysis to test the change of activity in the CAP component from myelinated fibers due to electrical charge applied by the blocking stimulation and there was no correlation (p=0.7). According to these results, the performance of neuroprostheses can be improved by a hyperpolarization block. Although the C fibers could not be blocked in all trials, when they did, the activity in the myelinated fibers was not significantly affected. Keywords: C Fiber, Unmyelinated, Frog, Hyperpolarization, Anodal, DC, Block.