Dear Fellows,
I just finished setting up a new whole cell recording rig in a new room. Currently I am testing the system. With proper groundings for devices, the recording reveals a noise around 120 Hz, using a model cell, as shown in the attached figure. Similar noise exists in recordings in hippocampal neurons.
Just wondering if any of you saw such noise before. Any suggestion will be highly appreciated.
Thanks
Hi Michel,
Thank you for your suggestions. Guess a humbug would be an easy and good solution as I already tried my best on grounding.
Thanks again
Hi Fading,
In addition to Michel recommendations, it is in general worth evaluating how much noise is acceptable for what you want to record. Even though it is definitively nicer to have as less noise as possible, you may realize that sometimes your noise level is not such an issue if you are recording large whole cell currents of nA amplitude. Arguably it is more critical when working with small currents or doing single channel recording.
This being said, make sure that everything is properly grounded. You should ground everything (including the Faraday cage) to a single point inside of the cage (you can use either copper wires or even better some mesh), and from there you go to the signal ground of your amplifier using a single wire. Also make sure you do not have cell phone around... Things like the air conditioning, or the compressor (if you use any) to bring air into your air table may induce spikes when turning on. So again make sure everything is properly grounded to minimize all of these external signals. One approach is to to assemble you rig with as less as possible equipment, check the noise, if everything is fine bring back one by one your different elements and see how it affects the noise level. That way you can identify if one particular element is causing this unnecessary noise. With time and method and will make it eventually without using any external noise silencer.
Hope this helps. Good luck!
Thank you, Norbert, for your detailed advice. I'm doing mEPSCs recordings from granule neurons in mouse hippocampal slices. The average amplitude of mEPSCs is around 8-10 pA, so with background noise about 4-5 pA it is hard for software to detect some small events.
Agree with what you said. I got this noise level under basic configuration with only amplifier, digitizer and computer on. Everything else was off and unplugged.
Also, very close to my room there are a row of different refrigerators constantly running all the time. Don't know if that could create any noise.
Anyway, I will keep improving my grounding skills while waiting for a noise silencer.
Cheers!
I second all that Norbert and Michel say; you're looking at 60 Hz noise, and the key is a single, solid ground. As always, less is better. This is true not only for the equipment (e.g., pumps - in my experience the worst!) in your Faraday cage, but also for the grounding. Going all the way out and "grounding everything" may actually be counterproductive, as it could introduce ground loops.
If everything fails, you can use an offline notch filter to get rid of your hum. Earlier mentioned humbug also does a good job.
Hi to all! As I recently experienced the similar situation I ask here instead of opening a new thread. The picture of the noise is attached (forget 50 Hz, it is on the open air high gain; peak-to-peak 120 Hz noise is of about 10 pA, which is crucial for mEPSCs).
I found out that the source of the noise is... Tadam! The silver wire in the pipette holder, the electrode itself! The grounding is OK, the front of Faraday cage is open but it does not cause the noise until I put the wire back into the pipette holder... Any suggestions?
Win XP, PatchMaster, HEKA EPC 10 double.
Is it possible that the noise comes from the silver wire which is fragile and about to be broken?
Dear Sheng-Nan, thanks for the suggestion, but the wire itself is OK: it is moderately thick (about 0.5 mm), well soldered in and the noise does not depend on whether the wire is freshly chlorided or already scratched.
Why did the biphasic deflection occur in the current tracing? For action currents, the deflection should be downward following by upward. Why did the current waveform turn out to be upward first, then downward afterwards? Is that cell-attached voltage-clamp recording? What is the level of holding potential applied in this condition? The baseline noise appears to be low and acceptable.
Case solved
To finish up the discussion of my case: the reason was very simple - just a connection with BNC cable from TTL-output of an amplifier to Trigger-input on the CCD camera attached on the microscope. I tried to synchronize the patch-clamp recording with image acquisition of fluorescence response and tested whether it would work. It did not for some reason, but I did not remove the cable between the amplifier and the camera after tests... Now it is removed and the noise is gone. Only one unanswered theoretical question - if that was just a ground loop, why the noise was not 50 Hz sine but 120 Hz spikes?
Thanks everyone for the answers and attention!
If you look at the periodogram of your noize, you will see the main 50Hz component and some harmonics that together combine into this spike-like shape.
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