Abstract
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•Physiological parameters for the crab walking leg nerve model of an unmyelinated fibre were optimised resulting in improved nerve health.•Developed protocol to combine improved bioimpedance measurement methods with previously reported unmyelinated fibre recording methods.•New, optimised method produced recorded data with single trace SNR ratios of ≥3:1, which resulted in a 10-trace average of an SNR of ≥9:1.•Demonstrated two methods in which to ascertain if the measured bioimpedance change is a genuine CAP dependent signal.
In mammals, fast neural Electrical Impedance Tomography (EIT) can image the myelinated component of the compound action potentials (CAP) using a nerve cuff. If applied to unmyelinated fibres this has great potential to improve selective neuromodulation (“electroceuticals”) to avoid off-target effects. Previously, bioimpedance recordings were averaged from unmyelinated crab leg nerve fibres, but the signal to noise ratio (SNR) needs improving.
Currently, functional non-invasive neuronal imaging is accomplished through surface electrodes or genetically expressed indicators that provide good spatial, but poor temporal, resolution. Here is an improved method for bioimpedance measurements from a model of unmyelinated fibres to enable optimisation through improvement of the 1) signal processing measurement paradigm, 2) neurophysiology, and 3) electrode-nerve interface.
For bioimpedance recordings, the recruitment and necessity of the CAP was quantified and saline significantly improved the SNR. An improved protocol resulted in averaging not being required, as sequentially recorded traces produced bioimpedance changes of −0.232 ± 0.064% that did not show phase or timing related artefacts.
Here, two bioimpedance traces displayed an SNR of ≥3:1, while previously over >100 averages were required with greater inter-experimental variability. 10 paired traces were averaged for an SNR of ≥9:1, or near real-time measurement.
This method facilitates further studies aiming to enable non-invasive localization of fascicular activity in unmyelinated fibres within peripheral nerves. This technique could ultimately produce the first 3-D tomographic images to help guide selective neuromodulation using bioelectric devices.