How to Calculate EEG Bands

EEG Bands

EEG readings are divided up in EEG bands: Delta, Theta, Alpha, Beta and Gamma (from slowest to fastest).

I figured that Wikipedia would have the standard range for EEG bands, but they list 3 different band ranges. (Note Hz means per second, so 3 Hz means 3 brainwaves per second)

https://en.wikipedia.org/wiki/Electroencephalography

Mindwave has their own definition, and if you google around you’ll see that so do most EEG readers and software.

http://support.neurosky.com/kb/science/eeg-band-frequencies

So there does not seem to be a standard definition of what each band name actually means. One person’s Gamma band can be quite different from another persons definition.

That’s why the Brainwave Analyzer has a default band ranges (similar to Wikipedia), but you are able to put in whichever range you prefer for whatever reason.

How EEG Bands are Calculated

Here is a one second sample of EEG readings, which you can download this file here:  

And then import into the Brainwave Analyzer.

Click on the “Analyze” button, then scroll down until you get to the “File Export” section.

Then, where it says “Export numbers table for all seconds”, click on “Download file”.

And this is what the downloaded file looks like:

See How to Calculate Frequencies and Amplitudes  where it explains how the Amplitudes correspond with the Frequency Index. For example, as you can see from the above screenshot:

• the Frequency Index of 1, has an amplitude of 9,110.124
• the Frequency Index of 2, has an amplitude of 3,132.592
• the Frequency Index of 3, has an amplitude of 2,886.606

Delta, has a frequency range of 1-3 Hz, so to calculate the Delta amplitude for this second, these 3 amplitudes are combined.

• Frequency Index of 1 amplitude squared:  9,110.124  x  9,110.124 = 82,994,359.295376
• Frequency Index of 2 amplitude squared: 3,132.592  x  3,132.592 = 9,813,132.638464
• Frequency Index of 3 amplitude squared: 2,886.606  x  2,886.606 = 8,332,494.199236

82,994,359.295376  +  9,813,132.638464  +  8,332,494.199236

= 101,139,986.133076

Square Root = 10,056.8377799921

Rounded Up = 10,056.84

(which is exactly what the Brainwave Analyzer calculated)

The great thing about EEG bands, is that they provide a useful way to summarize the large number of frequencies and amplitudes in each second of EEG readings.

You’ll notice that the slowest band is Delta with a frequency range of 1 to 3, meanwhile the Gamma band has a frequency range of 32 to 100. Because the slower brainwaves have much higher amplitudes than the faster brainwaves, the slower bands needs much fewer frequencies (Delta 1-3 Hz) to add up to amplitudes that are comparable to much larger numbers of higher frequencies (Gamma 32 – 100 Hz).

In addition, these band ranges are functionally based, such as Delta associated with sleep, Theta associated with drowsiness, etc…

For an EEG sample that contains minutes of readings, having summary results can be very helpful. For example if you download

The Brainwave Analyzer graphs look like:

    

Then, if you want to do your own graphing, you can download  a summary file, with band amplitude per second.

Where it says “Export band powers per second”, click on “Download file”.

And here is what the downloaded file looks like:

And using Excel you can make any kind of graph you like, including for example a Scatter Chart:

 

Also see How to Calculate Frequencies and Amplitudes