The yellow "Signal" bar: backgrounds and how to avoid that the bar supposedly is stuck

Via the yellow "Signal" bar (formerly "Reward") Cygnet indicates how much EEG activity of the very slow frequency range (low ILF) is currently recorded. For the certain games, the amount of measured "Signal" activity is then more or less directly translated into feedback parameter (e.g. the velocity of the rocket in InnerTube). Therefore, it is often assumed that the yellow bar graph is an indicator of the effectiveness of the Neurofeedback training, but this is not the case! A couple of users report that the yellow bar sometimes is not moving at all for several minutes. How can this happen?

The most likely cause of a stuck yellow "Signal" bar is a large jump in voltage during an EEG measurement at an electrode or at an electrode input of the NeuroAmp amplifier. Such large jumps in voltage can originate due to the therapists (mechanical) manipulation on the electrodes, e.g. when they are placed on the skin. Of course, such handling of the electrodes cannot be prevented but the therapist can avoid to touch the electrodes after the EEG recording has been started, i.e. when a session is running! Thus, it is strongly recommended to only start a session after all electrodes have been placed and after their impedances have been checked and evaluated to be fine (= green LED's).

However, there are also a few other sources of electrical voltages that interfere with the registration of very slow brain activity and will lead to a putative stuck yellow "Signal" bar: In the first minutes after attaching the electrodes, altering electrical voltages develop amongst the boundary surfaces of skin, paste and electrodes. Such voltages stabilize (equilibrate) only very slowly and – until then – might hardly be distinguishable from ILF brain activity.

The emergence of such equilibrium voltages cannot be prevented, but the therapist can take some measures to keep them as small as possible (see below). Another very helpful procedure is to start with the neurofeedback session only after such voltages have been stabilized. Thus, the attachment of the electrodes ideally is the very first step of any NFB session. This allows the equilibrium voltages to stabilize while the therapist conducts the interview with the patient and only thereafter starts the EEG measurement, i.e. the NFB training.

Not only at the start but also during the NFB training it is important that no large jumps of voltages are introduced into the system while EEG activity is recorded. Thus, prior to any action, like repositioning of electrodes or impedance measurements, a running session ALWAYS should either be paused ("Pause") or even completely stopped. Thereafter it is strongly recommended to not continue or restart the session until all such operations have been completed.

A final tip to reduce the amplitude of equilibrium voltages that emerge amongst the boundary surfaces of skin, paste and electrodes: In order to prevent these potentials from having to fully re-equilibrate each time after an electrode has been attached to the skin, it is recommended to leave some paste in the cavity of the electrodes after they have been removed off from the head of the patient at the end of a NFB session. For hygienic reasons, some paste might be wiped off superficially, but care must be taken to ensure that the paste in the cavity remains. In this way, the chemical environment at the Ag/AgCl surface of the electrode remains unchanged and the (equilibrium) voltages that have been formed there will not change too.

To keep the paste moisture while the electrodes are not in use it is recommended to cover the electrode heads with cling film. By such a procedure the "pasty" electrodes can be stored for many hours.

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