Introduction to EEGer4 & Neurofeedback General Concepts

EEGer4 is a software suite designed to provide visual and aural feedback based on electroencephalograph (EEG) brainwave signals. Neurofeedback is used to teach the brain to modulate excitatory and inhibitory patterns of specific neuronal assemblies and pathways based upon the details of the sensor placement and the feedback algorithms used, thereby increasing flexibility and selfregulation of relaxation and activation patterns.

Here is how the feedback process typically works:

1. The feedback loop begins with the client. Sensors 'pasted' to the client's head pick up microvolt-level EEG signals which are amplified and converted to digital voltages by the A/D subsystem at a nominal rate (usually 256 Hz).
2. The samples are converted to equivalent peak-peak voltages. All filters in the software are Infinite Impulse Response (IIR) filters. The raw samples are lowpass-filtered to remove 60 Hz ambient noise and threshold-limited to remove muscle (EMG) artifacts. The resulting lowpass signal is fed to a number of 'streams' of processing which are very similar.
3. In each stream, the lowpass signal is bandpass-filtered into various frequency bands (of the clinician's choice) using IIR digital filters. The filter output is fed to an exponentially-weighted moving average filter which produces a short-term average (peak-to-peak) voltage for further use. The time constant of the averaging filter is selectable but is usually 0.5 seconds. The moving average goes two places: directly to the client (game) software/display and to a comparator. The comparator produces a threshold-exceeded signal whenever the clinician-adjusted threshold voltage is less than the current moving average of the stream.
4. All the threshold-exceeded signals are processed by the reward decision logic which declares a 'reward' when streams defined as Inhibit are all below threshold and streams defined as Reward are all above threshold. Rewards are also limited at some rate so that each sound can be separately heard. The reward command is sent to the client computer/display.
5. The client software logic plays a prerecorded sound file (usually a short beep) whenever a reward is commanded, giving aural feedback to the client that all therapist-specified (amplitude) conditions were being met. The client software also draws simple graphics images giving a continuous (25 Hz) display of the ratio of amplitude to threshold for each stream of data.
6. The client's EEG response to the aural/visual signals is then sensed and fed back into the loop.

General Concepts

A neurofeedback system is comprised of four components: electrodes (sensors), amplifier/encoders, software, and the computer(s) used.

There are several manuals for EEGer4 users. The Operator's Manual contains information on all the controls and displays provided by EEGer4. The Technical Manual contains details about the interconnection of data for all the processing, the filter and (supported) device characteristics, and structures of various data outputs. All written resources can be found on EEG Software's support page, here.

Overall Operation

Typical overall operation consists of:

1. Selecting a client from the list of clients
2. (Possibly) reviewing the planned session
3. Beginning a session
4. Selecting a feedback display (game)
5. Making adjustments during the session
6. Post-session, reviewing the results.

EEGer4 has been designed to facilitate this process and automate full data recording.