IUBio

electroencephlogram database?

Breck Stapleton breckstapleton at msn.com
Fri Jan 18 10:09:34 EST 2002


ht_ at gmx.de (Heiko Tietze) wrote in message news:<3c473e46.84243495 at news.uni-wuerzburg.de>...
> 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. 

Yes, 2 Micro seconds is really short compared to 40 hertz or less, but
I do
mean Micro, 500 Khz or more,  perhaps even Nano seconds.  If  I hold
the
leads from my oscilloscope between my fingers, and look at a 20 micro
second
window,there are spikes at 2 micro seconds, around 200 milli volts. 
My scope won't go below 0.2  micro sec, so I can't get a better look
at the wave form.
These spikes don't  look random.  For a second or two these spike move
downward and then upward and then some up some down..


>                                                        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.

What if they are not artefacts, but information.


>                                  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)

Where can I find out more about gamma?



> 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.

So if there is information in the high frequency noise, an EEG
wouldn't see
it.

Thanks Heiko

Breck

p.s. I've sent this once before, but I seem to be having trouble with
this
news group.  Sorry if it gets posted twice.




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