When using the high-sensitivity MUSE, there is a way to reduce power supply noise without using a shielded room.
With this method, the remaining power supply noise can be eliminated even after the notch filter is used.
Fig.1 shows (a) the eyes opened before meditation in the living room with the room lights turned on. (b) Closed eyes and calmed down.
As you calm down, your brain waves calm down, so power supply noise (50Hz) becomes noticeable.
Fig. 2 shows a state where the eyes are closed and calm in a bathroom with a water-filled bathtub. (a) Turn on the bathroom light, (b) Turn off the light, then power supply noise (50Hz) disappears.
The bathroom is just an extreme case, but you can reduce the power supply noise mixed into the MUSE measurement data by choosing the appropriate place to meditate.
Additional notes (2019.10.23)
This data measurement was performed in a “dry” bathroom with the tub filled with “cold water”.