We are recording field EPSPs in CA3-CA1 synapses from 2-3-month old WT mice. We can get good EPSPs (size trace in blue) but during the baseline the EPSP gets small (yellow trace) and then large again and cycles over the course of the baseline.

As you can see in the traces, the EPSP changes in size but the fibre volley remains the same, so I don't think the electrodes aren't drifting. We also wrap our recording electrodes with cotton so droplets of aCSF do not form and land on the slice.

Please let me know if you have any suggestions of other things we can check. Thanks!