Re: number of electrodes

Actually, it does have a thing or two to do with physics and finances.

The electrode has to be large enough physically to be able to pick up the microvolt you're looking for.  Then, it has to be sufficiently distant enough from other electrodes to be able to be individually able to resolve its signal.  Then, it has to be far enough away that the common mode energy from one electrode doesn't interfere.  Touch two electrodes together, you get one big electrode.  When dealing with electrode sensors on a big resistor (the scalp and stuff under it) the electrodes will eventually merge electrically.  Figure an electrode's distance between each at most, and you have the limit.  The math involved to get an exact figure isn't really available at this time, but this is how it works.

Besides, if you're in your own home, and you're a hobbyist like I am, the actual limit is "how many amplifiers do I want to build into that really cool mixer?"  And "How long do I want to spend sticking wires to my head before I can see something meaningful on the screen?"  And finally, "do I have the cash for a really cool-looking EEG electrode helmet, like that cute ginger is modeling?"

Kevin

--------------------------------------------
On Thu, 2/26/15, Raj Mellacheruvu <[email protected]> wrote:

 Subject: Re: [Openeeg-list] number of electrodes
 To: "Discussion of EEG hardware, software, training protocols, NFB theory - for developers and users." <[email protected]>
 Date: Thursday, February 26, 2015, 2:14 PM
 
 Thanks Sharif.
 
 
 
 -----Original Message-----
 From: Sharif Olorin [mailto:[email protected]] 
 Sent: Wednesday, February 25, 2015 4:41 PM
 To: openeeg-list
 Subject: Re:
 [Openeeg-list] number of electrodes
 
 > Does anyone know why EEG systems have up
 to 24 electrodes and not more? what is the real limitation?
 Is it electronics?
 
 Do you
 mean OpenEEG systems, or EEG systems in general? If the
 latter, most medical/research EEGs have more than 24
 electrodes. I'm not sure about OpenEEG, but generalising
 from similar designs I'd guess it's something like a
 limitation imposed by the ADC chosen (number of channels),
 or just plain cost savings. I don't see any reason the
 design couldn't be modified to support more, it's
 certainly not a limitation in fundamental physics or
 anything.
 
 HTH,
 Sharif
 
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