What causes these artifacts in my electrophysiology recording? Large power spikes at many frequencies
Your guess of it being mains related is a good one.

It looks to me like the fundamental frequency is 150Hz - something like a mains powered motor would be my first guess.

If it's appearing &amp; disappearing, it's probably something on a fairly low frequency control cycle - like temperature control.

Try turning your air-con off while taking a measurement, or look around the lab for a chiller unit, air pump, something of that sort.

A good tip is to stick your measuring wires on something inanimate, that can be moved around - see if those frequencies are still there, and if they get stronger/weaker as they move around the room. At that point it's just playing hot &amp; cold to find the culprit.

Once you have found the source, either ensuring it is disabled while you are doing your measurements, or shielding it is possible.

Good luck!