tutorial for EEG electrical parameters?

Jean-Etienne Poirrier jepoirrier at nospam.free.fr
Mon Sep 30 04:03:09 EST 2002

Thanks a lot for your useful information. I think I begin to understand 
things better. And I did and will take great care of my rats, sure.


[posted and mailed]

"Dan Marquez" <dmarquez3 at socal.rr.com> wrote in
news:YOal9.58144$V7.14864089 at twister.socal.rr.com: 

> "Jean-Etienne Poirrier" <jepoirrier at nospam.free.fr> wrote in message
> news:amuhqd$hpu at aix4.segi.ulg.ac.be...
>> Hello,
>> I am using an electronix device to record EEG and EMG from rats. I
>> want to know what's inside the "black box" : what is a filter, a
>> bandpass, gain, etc. Do you know any interesting paper, book or
>> website providing this 
> kind
>> of information?
>> Thanks in advance.
>> Jean-Etienne
> I can also offer brief descriptions here.  If you look at a voltage on
> an oscilliscope, lots of times you see a wobbly line with a lot of
> noise. To get rid of the noise, filters are typically used.  Each
> filter has an input, where the noisy voltage is connected, and an
> output, which is the same voltage without the noise.
> But, there are different kinds of filters, and some are better than
> others. These are common filters...
> Lowpass filter - it allows low frequency voltages to pass through it,
> blocking high frequency noise
> Bandpass filter - it allows only a selected range of frequencies to go
> through
> Highpass filter - it allows only high frequencies to go through
> Notch Filter - it allows only one frquency to go through
> Gain is a number that you use to calculate the magnitude of an output
> if you know the magnitude of an input. For instance, an amplifier with
> a gain of 1000 will increase the input voltage by a factor of 1000. If
> you have a 1 millivolt signal at the input, you would expect to see a
> 1 volt output. 
> Amplifiers are very easy to make. A common component used to make
> amplifier is another amplifier called an "operational amplifier" (op
> amp).  This sounds complex but they are easy to use.  There are lots
> of cartoon-style books that teach how to use operational amplifiers. 
> Just to show how easy it is to make an amplifier, here's an example.
> Say you want a gain of 100. Just get a 100 kilo-ohm resistor and a 1
> kilo-ohm resistor and hook them up to an operational amplifier.  Done.
>  Well, sort of. You might see some noise and so you might add a
> filter. 
> There are different kinds of operational amplifiers. Some are very low
> power while others are very fast. You can configure op amps to make
> many common types of amplifiers, ranging from stereo amplifiers to
> ultra tiny operational amplifiers.
> EEG and EMG often use instrumentation amplifiers.  These are fancy
> names to op amp circuits that have really nice characteristics.  For
> instance, they don't drain a lot of current (like an audio amp might).
> They are generally resistant to static electricity, and they don't
> mess up when there is a noise called common mode noise. (But you don't
> need to know that.) But they will monitor voltages acoss different
> parts of the body. 
> Very often the voltages are converted to digital voltages so a
> microprocessor or computer can make pretty graphs or blinking lights.
> Hopefully your rats are generally happy with lots of room to play and
> lots of wood to chew. I believe lab animals should be treated with
> etopian courtesy.
> Dan

Jean-Etienne Poirrier, PhD student @ CRNCM/CRC - ULg
http://www.ulg.ac.be/cncm - http://www.ulg.ac.be/crc
http://jepoirrier.free.fr - jepoirrier on jabber.org

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