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alpha waves

Kevin Spencer kspencer at s.psych.uiuc.edu
Thu May 8 13:11:05 EST 1997


Alexander R Terrill <terrill+ at andrew.cmu.edu> writes:

>Excerpts from netnews.bionet.neuroscience: 7-May-97 Re: alpha waves by
>Kevin Spencer at s.psych.ui 
>> First, alpha activity is typically
>> enhanced when a person is "resting", that is, not engaged in a mentally-
>> demanding task but is asleep.  So I would say that enhanced alpha activity
>> is associated with relaxation.  It's one of the easiest EEG phenomena to
>> observe.
> 
>Exactly...
> 
>One correction though.  Alpha waves are present when the person is awake
>with the eyes closed. When the eyes are opened, other sensory stimuli
>impinge, or mental activity is performed, the alpha waves vanish.  This
>is called an alpha blocade.  These alpha waves are espicially deominate
>in the occipital area.  Therefore alpha waves have to be associated with
>"resting" because they go away with mental activity, sleep, and eyes
>open visual activity.  Even when you improve the signal-to-noise ratio
>averaging 128 to 256 sweeps there is little that can be seen in the 9-13
>Hz range. The lower amplitude beta waves (14 - 30 Hz) deominate.  In a
>sleeping adult the theta (4 - 7 Hz) and the delta (.5 - 3.5 Hz)
>deominate.  

I wouldn't say that alpha waves go away completely when the eyes are open
or the subject isn't "resting".  They don't dominate the EEG, but they
don't totally disappear either.  You will still see a peak in the power
spectrum in the alpha range when subjects have their eyes open and maybe
when they perform a task (depending on the task).  I use ERPs in my research,
and something interesting I see at times is a "rebound" in alpha activity
after the P300 component.

Kevin
-----------------------------------------------------------
Kevin Spencer
Cognitive Psychophysiology Laboratory and Beckman Institute
University of Illinois at Urbana-Champaign
kspencer at s.psych.uiuc.edu
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