28Hz/15Hz Interference

In setting up Low Energy Neurofeedback, it is common to run into the issue of interference from the electrical wiring surrounding the client. Sometimes this has been so severe that it has required that I set the bandwidth below 15 Hz to mathematically filter the “noise” from the EEG data.

An Inductor or “Choke” magnetically inhibits a changing electrical field. After spending some time learning about Instrument Operational Amplifiers, which are the “sense organ” of EEG systems, it occurred to me that the ground (green wire) ideally does not carry a changing electrical field and that I could filter all shifts in amplitude from this ground, or reference plane using a Choke. After trying this, I immediately saw a decrease (mostly elimination) of 15/28Hz latching. As far as I can tell it does not otherwise interfere with the EEG signal – I still see the LENS making changes to the EEG signal.

The Choke I settled on is a ~$5.00 Digikey part:

Here is the choke pictured as I use it

Choke attached to the ground wire

Another tactic I often use to combat interference is to put the amplifier on the client’s lap. This usually works well, and I think again relates to stabilizing the ground reference, similar to adding a choke (utilizing the client’s body as a large inductor).