electroencephlogram database?

Heiko Tietze ht_ at gmx.de
Thu Jan 17 16:32:12 EST 2002


On Thu, 17 Jan 2002 14:16:46 -0600, "Breck Stapleton"
<breckstapleton at msn.com> wrote:

>is there noise on the signals around 2 micro seconds, is there a pattern to
>the noise.
2 Microseconds are really short :) If you mean Milli this would be a
frequency at 500Hz which is not present in the brain. Short periods of
activity (spikes) does include high frequency, but its to mention that
nonsinusoidal activtiy is transformed by the Fouriertransformation
into sinusoidal representation. That means it is not shure that high
frequency are not an artefact. Nevertheless there are frequency bands
at the EEG:
subdelta/delta: <3Hz (sleep, coma)
theta: 3-6Hz (lower sleep stages, reported during subvigilant states)
alpha: 6.5-12.5Hz) (rest, most while closed eyes, the primary rhythm
at the EEG)
beta: 13-35Hz (sometimes divided in 3 bands) (activity, open eyes)
gamme: around 40Hz (consciousness, neural binding - a scientific area)
All frequencies are present at the moment, only the energy within the
spectrum depends on the task or state.
>Has any looked or is it just filtered out?
All can be done ;-)

At least: EEG amplifiers are timed with 200 or 256 Hz, up to 1kHz
normally so the upper time limit is less than a millisecond.

HTH, Heiko.


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