Hello,

I am trying to isolate the neural component from a nerve recording using a cuff electrode. Technically I am using a bipolar electrode, but when used with a differential headstage there is no signal, so I need to treat each lead as an independent electrode with a universal reference placed in the glands. I have experience recording neural signals in the brain, but am new to the periphery. Therefore, I am seeking advice regarding the next steps for how to identify which components of the signal are of neural origin (vs. cardiac, respiratory, etc)

With the nerve placed in the cuff, above any solution, we see a clear biological signal with periodic activity (Pic #1). Interestingly, we also see a similar signal but with a larger amplitude when the cuff is submerged in saline in the cavity, but is adjacent to the nerve (Pic #2). When I cut the nerve caudal to the recording electrode, the amplitude is somewhat reduced (Pic #3, compare amplitude with Pic #1). When both branches of the nerve are severed (just a floating section of nerve in the cuff), the signal becomes all noise because of the lack of continuity with the universal reference (not shown). However, when I use the open ephys software to treat one of the bipolar leads as a differential reference for the other lead I do see a signal (Pic #4).

Adding KCl and TTX to the cavity containing the nerve each reduce the amplitude of these events, but don't seem to impact frequency (Pics #5-6), whereas saline doesn't impact either metric (not shown). Obviously, I would expect TTX to eliminate neural activity and KCl to increase frequency.

To add to the confusion, when I stimulate the neuron using a differential stimulating electrode placed on the nerve caudal to the recording electrode, I see an immediate large event (3-5V) which is always followed by a smaller event (~150 uV) about 150 ms later. This second event has a much shorter half-width than the other events I have seen at baseline. Since the stim and recording electrode are < 5 mm apart, I am unsure what this event is because it shouldn't take that long to propagate along the nerve. I am wondering if the initial potential is drowned in the large stimulus artifact and the smaller event is the signal passing through the brain and returning down the nerve? Weirdly, when I apply TTX to the cavity, the 3-5V events disappear but the 150 ms delayed response (which is only seen with stimulation) remains. This makes me think that those 3-5 V events might be neural signals, however then we wouldn't have any stimulus artifact and the subsequent spike couldn't be return spike, since the initial event was precluded.

If anyone has experience with these recordings, I would really appreciate some advice regarding interpretation of these results and the next steps I should take for troubleshooting! Thanks so much in advance!