[Eeglablist] frequency subbands.....why???

[Emmanuelle Tognoli]

Dear Dorian,
An underlying reason for the use of subbands is that there are several
oscillations in each of those classical bands, with unique spatial,
spectral and functional characteristics. Those oscillations tend to be
difficult to tease apart, though my group has shown that high spectral
resolution and 4D visualization techniques (colorimetric mapping) are
tremendous aids toward that purpose.

Each of those oscillations (my group call them neuromarkers) has its own
"subband" for a given subject (no two subjects are alike), and at the
group level, the superposition of their spectral characteristics
concentrate (albeit imperfectly) in certain, neuromarker-specific,
territories of the spectrum (e.g. lower-alpha, mid-alpha or upper-alpha).
To give you examples, one usually finds the parieto-occipital alpha after
which the 10Hz band is named solidly in the center of the "alpha" band,
there is a medial mu activity that spread toward the lower alpha band (it
might cross-check an oscillation that Riitta Hari and colleagues called
"sigma"), and the lateralized (rolandic) mu rhythms stretch to the upper
part of the alpha band (right mu more so than left), a place in the alpha
"band" where one also sees a phi-complex under some circumstances. And
there are many other oscillations, less well characterized experimentally,
that one can see in just this alpha band. So the subband usually focuses
your attention on the "biggest players".

To summarize, dividing the bands into subbands is a heuristic to trying to
distinguish those several oscillations. Recall that frequency bands were
defined very early on in the history of electrophysiology at a time when
much less could be understood (no digital EEG, no spatially dense arrays,
no advanced analysis techniques), the classical bands have coarse-cut
boundaries and are only group trends for the phenomena that interested the
earlier investigators who defined them.

It is my very strong belief that an individualized approach to
neuromarkers (subbands specified on a subject-by-subject basis to account
for interindividual variability in spectral footprints) is essential, but
past that, subbands are a next best thing to provide a fine-grained view
on neural oscillations.

With kind regards,
_________________________________________________

Emmanuelle Tognoli - PhD
The Human Brain and Behavior Laboratory
Center for Complex Systems and Brain Sciences
Florida Atlantic University
777 Glades Road, Boca Raton, FL-33431
phone: (int+1) 561-297-0110
http://www.ccs.fau.edu/~tognoli


> Hi EEGLAB users and developers,
> Reading some EEG papers I've found that the Alpha and Beta waves are
> often divided into subbands. I'd really appreciate if someone can explain
> why there is this further divsion of the frequency spectrum and which are
> the differences between the subbands. I tried to look for some papers but
> I
> haven't found anything that is very clear and detailed.
>
> Thank you again for the support!
>
> Dorian
>
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