alpha waves

Alexander R Terrill terrill+ at andrew.cmu.edu
Thu May 8 07:46:04 EST 1997

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.
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)

Just my $ .02

                          Alexander R. Terrill
Carnegie-Mellon University   --wix at cmu.edu--   Cognitive Science & Biology

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