User Tutorial:Obtaining Mu Rhythm Parameters in an Initial Session

Although the basic properties of the Mu rhythm are identical for all human subjects, its spatial pattern and its exact frequency will differ. Thus, it is necessary to obtain these individual parameters prior to any feedback experiments, in an initial session. If your focus is on gathering experience with BCI2000 rather than actual feedback control by EEG, please read the paragraph on simulating an initial session below.

Experimental Design

In the initial session, the subject is instructed to imagine hand and/or feet movements according to a pre-defined pattern. To identify a subject's Mu Rhythm, the amplitude of the EEG signal is then taken for different frequency bands, and correlated with the instructions. Across frequencies, this results in a line spectrum; across electrode locations, the result is a spatial distribution of activity.

Performing the Initial Session

Start BCI2000 by double-clicking batch/StimulusPresentation_<YourAmplifier>.bat. For repeated use, placing a link to this file on the desktop might be a good idea.
In the operator module, click "Config".
Click "Load Parameters" to load the parameter file at parms/MuTutorial/InitialMuSession.prm.
Additionally, load the configuration file appropriate for your amplifier. For source modules available in the BCI2000 core distribution, amplifier parameter files are found in parms/amplifier. When using a source module from the contributions section, load the SignalGenerator.prm parameter file, and adapt it to your needs.
Under the "Storage" tab, enter the subject's initials into the "SubjectName" parameter.
Switch to the "Source" tab; into the "ChannelNames" parameter, enter electrode locations corresponding to amplifier channels, as a white-space separated list, e.g.

Fz CPz Cz CP3 ...

Instruct the subject as described in the next paragraph.
Click "Start".
The recording will finish automatically. If you want to acquire more data, just click "Resume" as often as you like.
Finally, click "Quit" to leave BCI2000.

Subject instruction

During the initial session, the subject's screen will either be blank, or display an arrow pointing up, down, left or right.

When a left or right arrow is displayed, imagine movement of the respective hand. The imagined movement should be continuous opening and closing of the hand, similar to rotating a tennis ball in one's hand.
When an up arrow is displayed, imagine simultaneous movement of both hands. This should be the same kind of movement as described for a single hand.
When a down arrow is displayed, imagine movement of both feet. The movement should be similar to the one described for hands, i.e. imagine opening and closing your feet as if you could use them to grip an object.
When you see a blank screen, please relax and stop any movement imagery.

Simulating an Initial Session

To get acquainted with BCI2000 before actually dealing with EEG, you may perform the initial session using the signal generator source module, using batch/StimulusPresentation_SignalGenerator.bat to start BCI2000.

In this case, the subject's brain state is simulated using the mouse cursor's position on the screen. Rather than doing imagery, move the mouse to the edge of the screen which is indicated by the arrow appearing on the subject's screen.

In the analysis, a signal modulation will be present but its topology will be different from what you expect for a human subject.

Analyzing the Initial Session

Use NN tool to obtain a feature map.
Look for vertically dominant structures at 9-15|18-30 Hz to identify the Mu Rhythm.
Check the topography for plausibility (compare to typical topographies).
Determine whether you have the pattern of a radial or tangential source orientation.
Determine the Mu Rhythm base frequency (must be exactly half of the second peak if unsharp).

Next Step

Configuring Online Feedback shows you how to configure the BCI system using the parameters obtained in the analysis.