1. EEG Analysis Methods Courtesy Dr Thomas F. Codura
Aamir Saeed Malik
Neuro-Signal Processing Group
Universiti Teknologi Petronas
Malaysia

2. EEG Analysis Methods Digital Filtering (IIR/FIR)
Butterworth, Chebyshev etc
Fast response, uses predefined bands (like 7 to 12 hz for alpha)
Like using a colored lens
Fast, useful for training & assessment
Digital clinical norms, live Z-scores based on digital filters (like joint time frequency analysis)

3. EEG Analysis Methods Fast Fourier Transform (FFT)
Analyzes all frequencies
Like a prism decomposes all lights
Response is slower because a block of data is required for FFT. Typically, its 1 sec past data & looking at mid of that half sec
Not useful for training because digital filtering can give immediate result for biofeedback & we can respond immediately
Its useful for assessment because it can be done a little later. We generally have time to make assessment

4. EEG Component Bands

5. EEG Bands Typical EEG component bands: Delta (1-4 hz) Theta (4-7 hz)
Alpha (8-12 hz)
Low Beta (12-15 hz)
Beta (15-20 hz)
High Beta (20-30 hz)
Gamma (40 hz and above)
Ranges are typical, not definitive
Anyone of these bands can occur outside the above frequency ranges
There may be overlap between these bands

6. EEG Bands
An example:
In this room, anyone above 5 ft 10 inches is male and below it is female
If true then we set these frequency ranges
If false then I change this figure, say 5 ft 9 inches
If false then we change again
If false such that one female is 5 ft 10 inches and one male is 5 ft 9 inches then we throw both of them out
That is, they are outliers and we reject them

9. EEG Bands
The EEG signal is closely related to the level of consciousness of the person
As the activity increases, the EEG shifts to higher dominating frequency and lower amplitude
When the eyes are closed, the alpha waves begin to dominate the EEG
When the person falls asleep, the dominant EEG frequency decreases
In a certain phase of sleep, rapid eye movement called (REM) sleep, the person dreams and has active movements of the eyes, which can be seen as a characteristic EEG signal
In deep sleep, the EEG has large and slow deflections called delta waves
No cerebral activity can be detected from a patient with complete cerebral death.

11. Delta Band It is a very diffuse slow wave
It is generally seen in sleep
It is often seen in injury, coma, brain trauma
Its is not sinusoidal, it is like a wandering wave
It is not rhythmic typically
It is caused by a variety of mechanisms, including slow neuronal mechanisms, DC shifts caused by Glial cells
It is often called an injury potential
There is a larger delta that is seen in waking up because eye opening, moving, muscle movement also show up in this EEG

12. Delta Band It is a very diffuse slow wave
It is often seen after epileptic seizures, the EEG is seen to wander around
Skin potentials can show up as delta
Slow cortical potentials can show up as delta

13. Theta Band It is typically from 4-7 hz It is non-sinusoidal wave
It is wandering and looks like a square wave
It is mediated by the sub-thalamic connections to the cortex
It tends to indicate either distractibility or a deep inward awareness or lack of presence
Its very common in attention deficit disorder & other types of disorders where brain excitability is not well regulated
It is also associated with memory retrieval
It is also associated with extreme creativity

14. Theta Band It is typically from 4-7 hz
Experienced meditators tend to exhibit theta during their meditation
It indicates an internalized state and a state of inward focus
In epilepsy & attention deficit people, an excess theta is seen
Since it is also associated with artistry & creativity, we are looking for appropriate amount of theta
So we look at ratios like theta to beta etc
Also alpha waves can slow down to delta range
Alpha slows down with age. The older you get, the more time you spend processing

15. Theta Band It is typically from 4-7 hz
So if a person is sitting with eyes closed & EEG is recorded
Lets say its 7 hz waxing & vanning sinusoidal. What is it?
Its alpha because theta is not waxing & vanning. It just come & go

16. Alpha Band It is typically from 8-12 hz
Alpha is the resting rhythm of the visual system
It is maximal at occipital
When eyes are closed, its largest in the back at occipital
It increases when eyes closed
It is very sinusoidal, very nice & smooth
It indicates that the visual system is at rest & not processing information
There is a reverberation between thalamus & cortex
It indicates that memory scanning is occurring

17. Alpha Band It is typically from 8-12 hz
Its background memory scanning (not the willful memory scanning like remembering phone no.)
Even there is memory scanning that you are not aware of. The brain quietly process information sorting it out
It could be slower than 8 hz & faster than 12 hz
It also does occur in other locations like frontal alpha & temporal alpha
Alpha are healthy rhythms & they need to be present at certain level (this will help us using Z-scores & normative data)
You need to have right amount of alpha

18. Alpha Band It is typically from 8-12 hz
Connectivity measures are important with alpha like coherence, synchrony and asymmetry
By looking at these measure of alpha, they are of tremendous diagnostic importance
For example, alpha synchrony is very healthy in an individual & it is also trained as biofeedback parameter even in people who are perfectly normal & want to have improved mental performance
Everyone can benefit from alpha synchrony training at the back of the head
James Hart has done it for decades & got good results

19. Alpha Band It is typically from 8-12 hz
There are variants of high alpha that are abnormal
For example, if you see large amounts of diffuse alpha in an individual & that alpha is seen to drone on & on – indicates anxiety disorder
That brain is adapting to chronic anxiety by saying that I am going to check out, I am not going to deal with it, I am not going to think or process etc. I am just going to make alpha waves
So it’s a paradox because this is a rhythm of relaxation, achieved in meditation while at the same time could indicate tension & anxiety
Excess alpha could also be some compensatory mechanism compensating for some other thing

20. Alpha Band It is typically from 8-12 hz
So, have to look at global & comprehensive picture using clinical science
So normative data & experience in reading recordings is very important

21. Low Beta Band It is typically from 12-15 hz
Some people call it 14 hz like Michael Tansey who is pioneer in this field
He used filter with pass range 13 to 15 hz so as to center on 14 hz
Some people use 12 to 16 hz
Low beta can also be called high alpha because names are not as important as to what's happening
This rhythm when observed over motor strip (C3, C4 & Cz) is called SMR (Sensory Motor Rhythm)
Filter

22. Low Beta Band It is typically from 12-15 hz
SMR is the alpha waves of the motor system
It is maximal at C3, C4 & Cz and it is maximum when body is still
Dr Barry Sterman discovered this rhythm in cats who were sitting still
SMR is maximum when brain intends to remain still
It is very exciting because it is a measurement that we can train (biofeedback & teach) for intention (not just behavior but also intention)
SMR deals with what I intend to do, what I plan to do
So when it is up-trained, it was found that individual becomes quiet, still, relaxed & are focused & remain in concentrated state
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23. Low Beta Band It is typically from 12-15 hz
The state where lot of SMR is being produced, it’s a very studious, quiet, healthy & pensive state
You can do maths problems in that state
You can read in that state
You can sit through a lecture in that state (It means your legs are not jiggling, you are not shuffling around in chair, you are not wandering about lunch & when the class is over)
Why its 12 to 15 hz?
The thalamic-cortical reverberations between motor strip & thalamus takes about 80 millisec from one way to other & then take 80 ms to get back
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24. Low Beta Band It is typically from 12-15 hz
The distance is that much shorter than the distance of thalamus to the back of head (Occipital)
The frequencies of these rhythms are directly related to the anatomy & physiology
So the reason that SMR is little bit faster than alpha is quite simply the fact that it is a little shorter trip to go from thalamus to central lobe compared to thalamus to occipital lobe
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25. Beta Band It is typically from 15-20 hz
Presence of beta is typically considered a thinking state
As we move to high frequency, the waves become more & more localized
For example, alpha could involve both hemispheres & you could have synchronous alpha for both hemispheres. People train whole head alpha
Low beta is typically more localized to one hemisphere or other (low beta synchrony across hemispheres is not done. Infact, it is asymmetry between hemispheres)
Beta is even more localized in a certain area
The reason is that the connections in brain that produce the beta waves are more cortical-cortical
Its one part of cortex talking to neighboring part in cortex
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26. Beta Band It is typically from 15-20 hz
So beta waves tend to be localized where the work is being done
Beta activity may be associated with memory recall when reading (more activity over motor strip)
Again there is a normal amount of beta
If you don’t see normative amount of beta, that means there is under activity (person may not be sharp enough, feeling depressed etc)
Beta is the sign of activation (how active you feel)
You need to use caution when you up-train beta
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27. Beta Band It is typically from 15-20 hz
Why use caution in up-training beta?
Generally, you are telling some part of brain to activate but you are not telling some other part of brain not to activate
Its like poking a tiger with hot rod – you don’t know if he is going to bite or run off or attack
There is too much going on when you try & excite the brain by up-training beta
If done rightly, the results very good in terms of brain sharpening & mood elevation
It should not be done in people prone to anxiety, mood problems etc
An alternative safer way is to down-train a low frequency. As a result, brain naturally shifts to high frequency
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28. High Beta Band It is typically from 20-30 hz People even go upto 35hz
At high beta, muscular activity can sneak in (EMG)
The only way to tell the difference between high beta & muscle activity is by looking at waves
Muscle activity is more like droning activity while high beta is more like waxing & vanning, true sinusoidal
High beta is associated with intensive thinking, worrying about things like doing a hard maths problem
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29. High Beta Band It is typically from 20-30 hz
Generally, guard (stop) bands used here so that artifacts like teeth grinding, muscular activity etc does not leak down to alpha
With kids, it is very important to observe them. They might make slight faces when nervous or otherwise and hence get desired waves & get reward
So it is important to tell them in detail & then also to observe them, otherwise, you might get false data
You need to tell them to be quiet, still, relax, listen/see & then ring the bell (for example)
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30. High Beta Band It is typically from 20-30 hz
With theta, its more like drifting away
With high beta, its thinking to solving problems
Normative data has been shown to distribute very well across cultures and regions all over the world
Everybody's brain is built pretty much the same way
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31. Gamma Band It is typically from 40 hz & above
There is more attention put on it since 2000
People have gone uptil 64hz & call it gamma
It indicates high level of sensory & perceptual binding
It may be an indicator that binding has occurred (researchers not sure)
What is binding?
Lets take a pen – I can move it in my fingers (motor interaction), I can see it from any side, I can hide behind & just feel it – but I know it’s a single object that is pen
There is no confusion in my brain what it is & brain sees it a single entity
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32. Gamma Band It is typically from 40 hz & above
Now little baby child do not have this ability
When its gone out of sight, its gone
When it comes again, its something new to them
We can smell ink of pen & we can hear if it has some button etc
So there is information coming from all of my sensory mechanisms (sight, sound, smell, touch, taste, memory)
To me this is this pen – That’s Binding
That’s sensory/perceptual/Memory Binding
On computers, we use these features for object identification but still we are far from it
Naturally, we do it immediately
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33. Gamma Band It is typically from 40 hz & above
A paper on Buddhist meditation shows that the gamma waves are synchronous across brain
This paper from Richard Davidson lab in Univ of Wisconsin
Its miraculous that these high freq waves (40cps) can actually be synchronized across the brain
The brain can’t transfer information that fast
There is underlying mechanism (sub-threshold mechanism) that takes care of this synchrony
It’s a theory that there are some sub-threshold gamma which become synchronized when some event occurs
Since it become synchronized all over the brain and all at once so it has to do with sensory & information binding
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34. Gamma Band It is typically from 40 hz & above
A native American healer was found to have 100hz gamma
There is also relationship reported between gamma & theta
When theta comes up then we see a burst of gamma
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35. Typical EEG Metrics

36. EEG Metrics Typical EEG metrics include:
Amplitude (microvolts)
Frequency (hz, peak or modal)
Percent energy
Variability
Coherence between 2 channels (percent)
Phase between 2 channels (degrees or percent)
Asymmetry between 2 channels (ratio or percent)
Possible Research Topic: New metric/feature for EEG assessment
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37. EEG Metrics Explanation of EEG metrics: Power (microvolts squared)
Amplitude looks at how big it is. We can have instantaneous amplitude at any time instant or we can have average amplitude
Typically average amplitude is over 1 to 3 sec
For assessment, average amplitude is even over a minute
There is phase relation between channels (exactly where the peak & valleys lie – are they in same phase or are their some separations?)
In some cases, phase separation is normal. For example, in language areas, the information goes back & forth when you talk/listen/read
So they do not operate synchronously and there is normal phase difference
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38. EEG Metrics Explanation of EEG metrics:
Asymmetry is very important – it tells us how different 2 channels are in amplitude
Most notable is the frontal alpha where the right alpha tends to be 10 to 15% larger than left alpha
This indicates a difference in cortical activation
If the brain waves at the frontal cortex are not asymmetrical, you will have mood problems (mood disorder, sad person)
Richard Davidson, Peter Rosenfield and few researchers from North Western in Chicago have worked in this and developed protocols
They have used it as therapeutic to assist people who are struggling with mood
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39. EEG Metrics Explanation of EEG metrics:
The underlying rationale is that left hemisphere is responsible for approach behavior & left frontal lobes are responsible for planning & executing approach behavior
The right frontal lobes are responsible for planning & execution of avoidance behavior
So the lobes for avoidance want to be less activated compared to lobes for approach behavior
You can switch when appropriate but it is important to have bias
Hence the right hemisphere makes more alpha so the right hemisphere is more relaxed
The left hemisphere is more activated
The general rule is that to improve mood, activate left more
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40. EEG Metrics Explanation of EEG metrics:
So it means inhibit theta/alpha/beta on left hemisphere
Push things down a little bit
That’s preferential then to enhance things on right because if you enhance things on right, you are not telling brain not to do it on left
As a result, brain tends to enhance both sides & unexpected results might occur
It has been found that asymmetry stretches to all bands except gamma
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41. EEG Metrics Explanation of EEG metrics:
Same is true for central lobes, C3 & C4
We want C3 to have little more speed/high frequency than C4
Typically, beta is trained on C3 and SMR on C4
The brainmaster have built in protocol that does that – it up-trains 15 to 18% at C3 & 12 to 15% at C4
So left hemisphere speeds up a little bit & right hemisphere relaxes a little bit
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