Fig. 2

Evoked ESRs are responsive to the anatomical location of the stimulating cathode. Representative data from subject S1. A Diagram of implanted epidural leads with the stimulating cathode located either on or off the intervertebral disc. Contact 11 (white square) on the second lead indicates the recording channel used to showcase ESR waveforms. Circular markers on the epidural stimulation lead indicate electrode contacts as either anode (yellow) or cathode (red). Dashed white horizontal lines indicate intervertebral disc based on x-ray projections. B ESR waveforms were represented as 300 individual traces with a median trace overlay at a stimulation amplitude of 4.0 mA. We further defined the ECAP window (1-2.5 ms) and EMG window (3-13 ms) for recorded ESRs. C Recorded ESRs from 8/8 contacts of the recording epidural lead were plotted to evaluate conduction velocities. The contacts located on epidural leads were ~7 mm apart from center-to-center. Large stimulation artifacts were observed in other recording channels (electrode contacts 1-6) located near the pair of stimulating electrode contacts. Cathodic ‘on-disc’ stimulation generated distorted signals within the ECAP window, with an estimated conduction velocity of 75.8 m/s, including visible EMG signals afterward (C1). When switched to the ‘off-disc’ stimulation, a more distinct waveform was recorded in the ECAP window, where conduction velocity was estimated to be at 70.9 m/s, with no observable signals in the EMG window (C2). Dashed line around 2.5 ms indicates the separation between the ECAP and EMG windows