Experiments
with the modularEEG
EEG-Feedback
Here are some infos about an EEG-Feedback session(from 2002-10-27) with
the
modularEEG.
Following session parameters were used:
- audio feedback
- filter center freq=9.4Hz, bw=2Hz
- feedback threshold=30uVp-p
- electrode positions:
- CH0: Cz-Au2
- DRL: on lower right leg
The recorded
data "021027alpha_fb.zip" (sorry, no more available here. Can be
requested via
email) can be viewed
(after unzipping) with bwview (
http://uazu.net/bwview/
bwview raw/256:s sessionname.pcm
) written by
Jim
Peters. Simply use the following command line: A description of the
events during ON-OFF-ON training marked in the
data:
021027alpha
fb9.4Hz th=30uVp-p ON-OFF-ON_EEGtxt.txt
BTW: The skin under the electrodes (Cz,Au2,pasted with 10/20 wax,
DRL
electrode
w/o) was unprepared. Due to moisture buildup during the session, the
electrode
impedance probably decreased. As a result the mains hum (50Hz spectral
line)
decreased over time.
Some screenshots of the session from bwview:
021027alpha fb9.4Hz th=30uVp-p ON-OFF-ON_EEG_M4.png
Same session, display mode m6:
021027alpha
fb9.4Hz th=30uVp-p ON-OFF-ON_EEG_M6.png
(2002-11-02)
ECG has a R-spike amplitude of about 1mV. Because the strong asymmetry
of
the signal, a total range of at least 2mVp-p for fullscale is
necessary.
To have headroom for movement artifacts etc. 4mVp-p would be desirable.
So in order to record ECGs with the
modularEEG,
the gain has to be lowered. This can be easily done by replacing e.g
R214
and R215 (for channel2, modEEGamp_v0.05) with 100k. The gain of the
first
stage is thereby lowered from 12.2 to about 1.(BTW: This is not the
best
way to lower the total gain, because the signal to noise ratio of the
INA114
is better when using higher gains).
The current version modEEGamp_v1.1.0
(2003-11-01) does not need the above modifications. Simply adjust P202
and P203 to the lowest available amplification and you can record ECGs.

(picture: ECG voltage over time)
The
recorded ECG data can be viewed with
bwview
(
http://uazu.net/bwview/) also.
Simply
use the following command line:
bwview raw/256:s sessionname.pcm
In the the joint time-frequency-display (JTF) a periodic modulation of
the
heart rate from ca. 1.1Hz to 1.3Hz can be seen. This is due to
respiratory
sinus arrhythmia (RSA).
Respiratory
Sinus Arrhythmia
In healthy hearts, heart rate varies across the
breathing
cycle.
Heart rate increases during inspiration and decreases with expiration.
This
pattern observed in normal hearts, is misleadingly called the
respiratory
sinus arrhythmia (RSA).
RSA depends on parasympathetic (vagus nerve) regulation of the
heart.
While disruption of vagal signals to the heart almost completely ends
RSA,
interference with sympathetic signals does not affect it (Papillo &
Shapiro,
1990).
The RSA indexes the heart’s adaptability to changing demands.
Ideally,
a patient will show a large-amplitude RSA that is perfectly in-phase
with
respiration. The RSA may be reduced or absent in thoracic breathers and
paradoxically
when breathing is too slow. The absence of an RSA may be a strong risk
factor
for heart attack.
Cited from
http://www2.truman.edu/shaffer/cardio_2001.htm
(a part of the Biofeedback bootcamp):
(The above URL is invalid now, but mirrored at
http://www.psychosensory.com/files/bootcamphome_2001.zip,
6.5mb)