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What's a Brain Wave?

dag.stenberg at helsinki.nospam.fi dag.stenberg at helsinki.nospam.fi
Sun Apr 18 13:16:46 EST 1999


Wolfgang Schwarz <wschwarz at zedat.fu-berlin.de> wrote:
> There are gadgets that claim to cause "Brainwave synchronisation"
> (e.g. the once famous "Brain Machine" or even the sample editor "Cool
> Edit"). That should lead to trance states or something like that
> (never works in my case though). Is that just nonsense then, or what
> are these gamma- and thetawaves they allegedly induce?

As others have pointed out, "brain waves" usually refer to EEG activity
(eletroencephalographic activity), i.e. the summation potentials of
large amounts of cortical neurons. The frequencies reflect synchronous
activation of many neurons. 
  Gamma waves have a frequency of more than 30 Hz (30 cycles/sec), have
small amplitude and are thus hard to record. They occur mainly during
focussed attention in wakefulness.
  Theta waves have a frequency in humans from 4 to 8 Hz, are not very
regular, and mostly occur during drowsiness and sleep.
  There are other "named" frequency bands: alpha from 8 to 13 Hz, occurs
mainly during relaxed wakefulness in the occipital regions of the skull.
A mental state dominated by aplha frewquency is described by some as
"relaxed", bo others (like me) as unbearable tiredness (I like to be
more active than that).
  Delta from 0.5 to 4 Hz is irregular and occurs mainly during deep
sleep. Sigma from 11 to 15 Hz occurs in 1 second bursts during sleep, 
and can be seen most easily during light sleep, when delta is still not 
too strong.
  Beta from about 15 to 25 Hz has low amplitude, can occur at any time,
but is said to reflect weakefulness simply because during active wakefulness
one does not have the other, larger waveforms. The slower a waveform is,
the larger it tends to be in terms of electrical amplitude.

  Trance states reflect a certain pattern of brain activity; EEG waves
reflect a certain pattern of brain activity; thus: if you induce a
certain brain activity state, you will see that type of EEG activity.

Dag Stenberg
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Dag Stenberg     MD PhD                    stenberg at cc.helsinki.fi
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Department of Physiology                   fax: (int.+)358-9-1918681
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