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GEORGIA INSTITUTE OF TECHNOLOGY
College of Engineering
School of Electrical and Computer Engineering
ECE 4006
Senior Design
EEG Control Background Report
Spring 2002
Jonathan James
Matthew Morgan
Da’Janel Roberts
Date Submitted: January 29, 2002
Purpose
Our purpose is to study electroencephalography (EEG) theory and determine whether last
semester's group succeeded in building an amplifier that captures brainwaves. If they were in
fact successful we will try to improve upon their design and digitize the output for use by the
digital group, who will then interface the amplifier to a computer and control a RC car. If they
were not successful, our goal then becomes to build an amplifier that will magnify neural
impulses so that they can be measured and interpreted. In order to begin, we must first
understand the basic ideas behind EEG.
EEG Theory
Within the human brain, there are over 1011 nerve cells functioning to convey information
throughout the body. Nerve cells, commonly referred to as neurons, present electrical
differences with relation to the cerebral liquid in which it is immersed. An action potential is a
brief fluctuation of the electrical charge in the membrane of the neuron [2] caused by the rapid
opening and closing of ionic channels. The evolved action potentials flow as waves through the
neuron’s axon, transferring cerebral data throughout the nervous system. Hence, it is the
summation of the electrical activity of millions of neurons that constitute brain waves [2].
Similar to fingerprints, brain waves, which are principally located in the cortex, are very
unique in their appearance. Because of their intricate uniqueness, specialists have categorized
the waves based on a series of characteristics. Amongst the various types of characteristics,
frequency, shape, and amplitude are always used when determining the class of the brain wave
[5]. Because the precision of a frequency analysis is high, waves are typically recognized by
their frequency. By categorizing brain waves according to the aforementioned characteristics,
the consciousness of a subject can be determined. Additionally, the emotional state can be
predicted. Five groups: Alpha, Beta, Delta, Theta, and Mu waves are among the most common
brain waveforms that have been recorded and studied and will be discussed in more detail in
subsequent paragraphs.
Due to the eagerness to attain knowledge about brain waves, scientist Hans Berger
established the science of Electroencephalography, designed to record the instantaneous
electrical currents produced by the human brain. Using this science, a plethora of neurological
specialists have revealed functional abnormalities of the brain, especially for the evaluation of
comatose states. Hypotheses have since been developed encouraging the notion that pyramidal
cells of the cerebral cortex are the source of EEG, an acronym for Electroencephalogram,
voltages. EEG is a device that registers the brain’s cellular activity through a person’s several
states, recording the activities from their being awake to being in a deep sleep [2]. The data is
received via detectable electrodes attached to the scalp because measurements on the scalp can
detect the underlying electrical patterns of masses of neurons in an attenuated and unfocused
form [1]. The electrical voltages conduct up through brain tissue, entering the membranes
surrounding the brain continuing up to the scalp where they can be measured by the electrodes.
Alpha waves are very recognizable in EEG recordings. The frequency range for alpha
waves is 8-13 Hertz. These waves are usually high in magnitude and are frequently emitted.
Alpha waves are indicative of a state of relaxation, reflecting, or any period of depleted
attentiveness. Alpha is the brain wave belonging to the part of the brain that deals scope,
spiritual and physical. Meditation and hypnosis are done in alpha waves because they tend to be
present posteriorly more than anteriorly {5]. An example of the activity of alpha waves can be
seen below.
Figure 1. Alpha Waves.
Beta waves are imperative for any form of productivity. High frequencies from 14 to 30
Hertz makes beta waves the fastest EEG waves and signal an active cortex and an intense state of
attention. These swift waves are accompanied by an extremely low amplitude. A person is
awaken and active during this period. Information is typically being processed during this state
as a result of heightened mental activity [4]. Beta wave characteristics are displayed below.
Figure 2. Beta Waves.
Theta waves are smaller than the two wave groups mentioned above. This could be
attributed to the fact that a subject is probably dreaming when these waves are recorded. Theta
waves usually represent drowsiness, feelings of emotional stress such as frustration and other
intuitive states [4]. Spike-like waves at a frequency of 3-7 hertz can be expected [3]. The
amplitude of the waves vary from low to medium. Such characteristics can be viewed below.
Figure 3. Theta Waves
Delta waves possess very distinctive characteristics out of the five groups. A maximal
frequency of 3.5 Hertz may be seen during this state [3]. High amplitudes are prevalent and are
probably the result of simultaneously firing of synchronized neurons. When delta waves are
present, the person is deep asleep, totally subconscious, or non-attentive. Delta waves are
however, abnormal in an awake adult.
Figure 4. Delta Waves
Mu waves, the fifth group, are not primarily distinguished by their frequencies but their
shape. Mu waves resemble croquet wickets in shape[4]. They are rounded in one direction with
a sharp side in the other direction. The frequency is one half of the beta activity. Mu waves are
associated with the physical movements or the intentions to move. They are more evident when
over the motor cortex and in the parasagittal regions[5].
Figure 5. Mu Waves
Current Technology
There are several products on the market today that will read these brainwaves. These
machines are most often used in a field of alternative medicine referred to as neurofeedback or
EEG biofeedback. Neurofeedback is a technique that enables participants to improve mental
performance, normalize behavior, and stabilize mood by simply watching their own brainwaves.
This technique has been shown to have positive effects on anxiety, depression, leaning
disabilities, sleep disorders, as well as many other mental problems. Most of the equipment that
can read EEG signals was designed for this purpose, and consequently, are very specialized and
costly.
ProComp+ by Thought Technology
The ProComp+ is a general biofeedback device that can read EEG, electromyography
(EMG), electrocardiography (EKG), blood volume pulse (BVP), skin conductance (SC),
respiration and temperature. The base machine costs $3500 with the various add-on modules
costing between $250 and $350. The ProComp+ reads EEG signals between 0-40 Hz, sampled
at 20 - 256 Hz. More detailed information can be found at http://www.thoughttechnology.com.
Unfortunately, the high cost of this system makes it impractical for our use.
Mindset by the Aquathought Foundation
Unlike the ProComp+, the Mindset was designed for research applications instead of
biofeedback. As such, the Mindset specializes in reading EEG signals. The machine has 16
differential input channels using a 16-bit A/D converter that can read 1024 samples-per-secondper-channel (programmable from 64). The Mindset also uses 2 fourth-order Sallen-Key active
filters that provide a 48-db roll-off per octave and has a passband of 1.8 Hz to 36 Hz. This
system looks very appealing from a hardware perspective. Being a research oriented tool, the
software for Mindset is based on a completely open architecture. Surprisingly enough, the price
for the Mindset is much lower than the ProComp+. For research purposes the Mindset costs
$2195. The Computer Science department at Colorado State University has already been using a
Mindset in their research, and considering the open software architecture, price, and hardware
quality, this system might be a worthy investment for future Georgia Tech EEG projects. More
information can be found at http://www.aquathought.com/mindset.html.
WaveRider series by MindPeak
The WaveRider series consists of the WaveRider Pro, the WaveRider Jr., and the
Cognitive Efficiency Organizer (CEO). The WaveRiders are similar to the ProComp+ in that
they are general purpose biofeedback devices and do not specifically focus on EEG. The
WaveRider Pro is a 4-channel device that monitors EEG, EMG, skin resistance, and heart rate.
The WaveRider Jr. only has 2-channels, while the CEO is limited to 1. Each of these machines
have a .5 Hz to 40 Hz passband with a lowpass filter that drops to –72 db around 60 Hz. They
use an 8-bit A/D converter and can capture 128 samples-per-second. While the WaveRiders are
not as sophisticated as the ProComp+ or the Mindset, they are less expensive. The Pro sells for
$1700, the Jr. for $950, and the CEO for $545. The CEO looks attractive for a low cost EEG
machine, yet the limitation of one channel could hinder further growth of our project.
BrainMaster 2E by BrainMaster Technologies
The BrainMaster is a 2-channel device that can record brainwaves or related signals such
as EMG. The BrainMaster amplifies signals between 1.6 Hz and 40 Hz, with a gain of 20,000.
The signal is digitized using an 8-bit A/D converter and gives 120 samples per second. It sells
for $975. All in all, the BrainMaster appears to be comparable to the WaveRider Jr. However,
the BrainMaster does have the advantage of open hardware. Thomas F. Collura, the designer of
the BrainMaster, has released schematics for his amplifier design. These schematics were used
by last semester’s group to build their own amplifier.
Last Semester’s Amplifier
This amplifier uses the plans for an old version of the brainmaster,
http://www.brainm.com, developed by Thomas Collura. The circuit is a two-stage amplifier as
can be seen below:
Figure 6. Schematic of last semester’s design.
This design was implemented last semester but not thoroughly tested. And so our job will be to
prove this design works, and hopefully measure EEG signals.
References
[1] http://www-users.york.ac.york/~scf104/brain-research/EEG-recordings.html
[2] http://www.epub.org.br/cm/n02/mente/neurobiologica_i.htm
[3] http://www.serv.net/~only-legg/biology/biograph.html
[4] http://members.aol.com/AB25M/brainwaves.html
[5] http://emedicine.com/neuro/topic275.htm