I am a novice in EEG, and also not a native speaker of English.

I am reading through the article A revised glossary of terms most commonly used by clinical electroencephalographers and updated proposal for the report format of the EEG findings. Revision 2017 in Clinical Neurophysiology Practice. There it distinguishes the alpha rhythm and rhythms of alpha frequency. In the definition of alpha rhythm:

Rhythm at 8–13 Hz inclusive occurring during wakefulness over the posterior regions of the head, generally with maximum amplitudes over the occipital areas.

Which, I read, refers to that alpha wave we also know as the PDR (posterior dominant rhythm). Notably,

“[others in this frequency band]... should either have specific appellations ... or should be referred to as rhythms of alpha frequency or alpha activity.”

Ok. Then, I expected alpha wave to be generic, defined as waves in 8–13 Hz. However it read:

Alpha wave: Wave with duration of 1/8–1/13 s (77–125 ms).

As I understand, duration of a wave (as in physics) is different from its period. A period is the inverse of frequency, while duration is either the time the wave continues, or the time of single up and down which doesn't cycle. The glossary itself has an entry for duration:

Duration: (1) The interval from beginning to end of an individual wave or complex. Comment: the duration of the cycle of individual components of a sequence of regularly repeating waves or complexes is referred to as the period of the wave or complex. (2) The time that a sequence of waves or complexes or any other distinguishable feature lasts in an EEG record.

So it seems to me that it's either (1) The glossary is inconsistent in its wording, or (2) alpha wave as defined here is for single complex (similar to spike or sharp wave) that is characterised by its length in time. Either isn't very convincing for me: (1) They took their trouble ommiting the word frequency and using 1/8-1/13 instead of 8-13, would they use confusing wording? (2) From what I have gathered, this definition is used by a distinct minority (if any).

My question is:

  • Is the glossary inconsistent? Can I understand the alpha wave defined there as Wave with frequency of 8–13 Hz?
  • If not, can I understand this alpha wave as a name for non-cyclic activity? How widely is this definition used? Any other usuage of alpha wave I encountered simply refers to a continuous oscillation with frequency of 8–13 Hz.

1 Answer 1


I personally don't see the contradiction. It seems very contrived from your end to establish that there is one. I think it's very clear from the definition of the alpha wave that 'duration' is synonymous with 'period' in that case. In the 4th quote, defining 'duration', it even says this outright, "The duration of the cycle of individual components of a sequence of regularly repeating waves or complexes is referred to as the period of the wave".

Basically, looking at the definition of alpha wave where duration in that specific case equals period, solves everything. It's the most intuitive answer. Would it have been better if they had written 'period' instead? Probably. But to pick up on that definitional ambiguity, not see their definition of duration also includes that of period, and somehow claim that this implies people are defining alpha waves for non-cyclic activity is an enormous stretch.

The glossary's definition is correct and you can understand the definition of an alpha wave as a wave in the 8-13 Hz band / a wave with a period of 1/8 - 1/13 seconds.


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