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alpha waves

Dag Stenberg stenberg at cc.Helsinki.FI
Wed May 21 00:12:59 EST 1997


In bionet.neuroscience Curt Siffert <siffert at shell.> wrote:
>     is as follows.  They do a head map to start out, which is 
>     putting an electrode at a place on the head and measuring the
>     activity, and then taking it off and putting it on a new place,
>     etc... for something like 22 different locations.  

I suppose that for this purpose using only one electrode at a time does
not lead to any terrible loss of information, although the fact is that
different frequency ranges may have different areas of dominance, so
they are probably optimizing for alpha.

>	I'm aware of the four basic brainwaves, 

I would not call them "basic brainwaves". Dividing the EEG frequency
range into four bands is just a way to simplify talking about
frequencies. A person's alpha might actually be at say 10.5 Hz, and
still the detector will dump everything from 8 to 13 under that heading.
In this example, the actual physiological function will be something
driving cortical neurons at 10.5 Hz, and any activity at say 9 or 12 has
no relation to that physiological function at all. In the case of alpha,
we are talking about a highly regular, physiological function, but in
the case of beta, theta and delta, the underlying process is much more
irregular, and not even a homogenous physiological function. It is true,
though, that slow (theta and delta) frequencies dominate during sleep,
and beta frequencies are easier to see when neither slow frequencies or
alpha dominate. For many physiological phenomena, the pattern of
occurrence of the waves (long runs or intense, short bursts) is as
important as the actual power content in a band, and the analyzer may
not reveal this temporal pattern.

> 	although this also measures 
>     "high beta" and another set that seems to lie between alpha
>     and beta (SRE or something).  I assume these are just further
>     breakdowns of Hz ranges.

In fact, the SMR or sensorimotor rhythm (I suppose that is what is meant
here) is another basic rhythm, quite regular and somewhere between 12
and 15 Hz depending on the individual. It has a different (smaller) 
distribution from alpha, and would otherwise with some apparatus 
(not really measuring the ongoing activity but just power or 
square of the power in broad frequency bands) be difficult to 
separate from alpha. This is a basic rhythm with a physiological 
function.

>     I'm not really sure what that means in terms of a high readout, like
>     if a high readout means the waves have high amplitude or what.  But
>     someone wanted to know what it measured, so there's the answer.

It probably means just that. 

>     People should be able to move from one state to another relatively
>     easily, to be able to concentrate when need be, relax when need be,
>     fall asleep, wake up, etc.  

Please do not confuse dominance of one of the frequency bands discussed
above with a physiological "state". While it is true that the EEG
is different in different vigilance states, broad band analysis from
just one scalp location at a time is a much too crude measure to define
a "state", except the well-known alpha dominance in posterior head areas
during waking relaxation. Correlating the EEG to consciousness states is
perhaps not a main concern of people trying to get more out of the EEG,
but nevertheless there is much literature about it - and not made with
broad-band flashing-lights analyzers either. EEG brain mapping has
improved with the computer boom. The journals "Electroencephalography 
and Clinical Electromyography" and "Neuroreport" are two that come 
to mind as literature sources, but there is more.

>     The system draws a correlation between these states and the 
>     brainwaves.  For instance, if one is stuck in alpha, it would 
>     be very difficult for him or her to achieve these other states 
>     of consciousness.
...
>     "Getting beyond alpha" just means having the ability to more 
>     flexibly go from state to state.  

I think it might be helpful here to find scientific literature 
that showed the correlation between the output of that particular 
brain wave analyzer and consciousness states. (Actually I somehow doubt
that there is any). It does not help to say that "brain waves 
correlate to consciousness states", because while this may be true 
(depending on what type consciousness states we are talking about), 
the correlations have been shown with much more sophisticated
equipment, and may be subtle and show interindividual differences. 

I have not been active on the waking side for quite some time; if
somebody would like to point to specific items in the scientific 
literature, I am sure that would be of great interest to this group.

Dag Stenberg

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Dag Stenberg     MD PhD                    stenberg at cc.helsinki.fi
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