Nerve Excitability Testing

Nerve excitability testing (NET) may assess the excitability of small and large peripheral nerve fibres [1]. A nerve excitability test consists of electrophysiological assessments of excitability properties such as the strength-duration relation, accommodation properties, recovery cycle, etc. The excitability properties of the peripheral nerve fibre may be linked to ion channel properties through computational modelling [2].

LabBench® offers NET in the form of Perception Threshold Tracking. When performing the perception threshold tracking technique, either small or large cutaneous nerve fibres are activated by specially designed electrodes. Small cutaneous nerve fibres terminate in the epidermis and may therefore be activated by electrodes with small cathodes [3]. Large cutaneous nerve fibres terminate in the dermis and may be activated by standard stimulation electrodes.

The perception threshold is assessed by applying a series of electrical stimulations. Labbench has several threshold estimation methods implemented, from which the PSI methods seem to be the most time-efficient [4], [5]. The perception threshold is estimated for several different pulse shapes. E.g., a series of rectangular pulse shapes will assess the strength duration relation [1]. In contrast, a series of triangular pulse shapes will assess the accommodation properties of the peripheral nerve fibre [6].

Large fibre excitability testing may be performed by conventional threshold tracking, but this technique does unfortunately not allow for small fibre testing [7].

Experimental Protocols

In Perception Threshold Tracking a subject is presented with an electrical stimulation, and the test consists of determining the minimal intensity that will elicit a response and thus can be perceived by the subject. By using electrical stimuli that consists of varying shapes and contains conditioning stimuli different biophysical mechanisms can be studying in the nerve fibers. Below are given examples of what kind of test procedures that can be performed with Perception Threshold Tracking.

Strength-Duration Curves

Strength-duration (SD) curves are performed by determining the threshold to electrical stimuli of increasing duration. The durations typically range from 50us to 2ms. From the SD curve, the chronaxie and rheobase can be determined. The rheobase is the minimum current that can elicit a response to a pulse of infinite duration. The chronaxie is the minimum duration that can elicit a response when the intensity of the pulse is two times the possible. Consequently, the chronaxie measures the slope of the SD curve. An alternative measurement for the slope of the SD curves is the strength-duration time constant.

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Threshold Electrotonus

With threshold electrotonus, nerve fibers are conditioned with long duration subthreshold pulses of typically 100ms in duration. The test consists of determing the minimal intensities that will elicit a response to a short duration test pulse of typically 1ms in duration. The test pulse is given at an inter-stimulus-interval from the onset of the conditioning pulse ranging from typically 0ms to 200ms.

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Accommodation Curves

Accommodation curves are performed by determining the minimal intensity that will evoke a response to ramps. The ramps have a typical duration from 1ms to 200ms.

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Available Products

LabBench

LabBench is a program for studies within neuroscience which allow an experimenter to perform experiments based on predefined protocols.

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LabBench I/O

The LabBench I/O are response and stimulus devices for electrophysiology and psychophysical experiments. With these devices, you can collect responses for threshold estimation with a response buttons or psychophysical rating scales.

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References

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