The condition is that the nerve has been pinched (essentially destroyed so no action potential gets conducted along the nerve) and then is being electrically stimulated to produce action potentials. Stimulus voltage is 60V.
I get this weird bump (like a decaying sine wave) in the compound action potential trace after the shock artifact instead of a flat line. What could be the reason for this?
Hello, Sanjay!
I seems like you have amplifier with active noise cancelling at 60 Hz, which has a period of oscillations equals to 1s/60 = 0.016(6) s = 16.7 ms. This active filtering injects a current with the same frequency of 60 Hz (as in A/C in your room), but in opposite phase, which is added to the output of your amplifier and reduces background 60 Hz noise, but only in the absence of external stimulus.
However, during short and large external stimulus (like you have on your figure), the active noise cancelation also injects relatively large 60 Hz signal to compensate the 60 Hz component of the stimulus, which is in your case is about 30 mV. Since there is no additional 60 noise, the 60 Hz component from the active noise cancelation attenuates within next 50 ms. That is why you have this "decaying sine wave" with a period of about 16 ms.
To solve this problem you need to turn off your active noise compensation completely. This may lead to a small increase in 60 Hz background noise, which you can reduce by additional grounding of your Faraday cage, or your sample chamber with an additional aluminum foil screen, for example.
Thank you Dr. Kabakov for your answer. However, I am not sure where on the amplifier I can switch off the active noise compensation. I have attached my amplifier settings.
I am not 100% sure about your specific amplifier, but try the following.
1. Without any biological preparation try to do a mock "experiment" with the solutions only, by positioning your recording electrode and stimulus electrode in their usual positions in the chamber with the solution. Then your mock "experiment" should produce the same "decaying sine wave". If there is no "decaying sine wave" then my explanation is wrong and you need to look for another answer.
2. If the "decaying sine wave" is there, then change the NOTCH switch position from IN to OUT position. This should change the polarity of the "decaying sine wave" to the opposite, which will be a confirmation that the amplifier has active noise compensation.
3. Probably, if you turn your "CAPACITY COMP" knob completely counter clockwise (perhaps you will feel a click), the active noise compensation will be turned off, and the "decaying sine wave" will disappear.
Good luck!
I'd agree that the use of the notch (actually a passive filter process) is most likely sending the saturated amplifier into an oscillation which it takes some time to recover from. Turning off the notch filter will likely remove this, but will result in more 60Hz interference. However, an active noise cancellation device such as the Digitimer Humbug (or multi-channel D400 will more effectively remove the interference without causing oscillation after the stimulus artifact.
https://www.digitimer.com/product-category/life-science-research/mains-noise-eliminators/
- Badges
- Science topic
- Similar topics
- Linguistics
- Composition Studies
- Writing