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- From: wtm@uhura.neoucom.edu (Bill Mayhew)
- Subject: Re: How does EEG's work?
- Message-ID: <1992Dec13.031541.10329@uhura.neoucom.edu>
- Organization: Northeastern Ohio Universities College of Medicine
- References: <cantrell.724092668@sauron.msfc.nasa.gov>
- Date: Sun, 13 Dec 1992 03:15:41 GMT
- Lines: 48
-
- The best place to start is to go to a medical library and check out
- books on neurobiological techniques. My experience has been from
- being a volunteer subject. An electrode is designated as an
- indifferent from which potentials will be measured. Following a
- chart of standardized stereotaxic coordinates, other electrodes are
- placed on the scalp. Occasionally, a second reference electrode is
- placed on the head to pick up electromyographic response from eye
- blinks, and other facial muscular response. This is helpful for
- removing muscle artifact from the EEG response.
-
- The electrodes are usually small gold (plated?) cups that are
- filled with a conductive paste that looks like toothpaste. The
- electrodes are taped in place. Removing the tape and getting the
- paste out of your hair later on isn't a lot of fun, but this is
- science, you know. I belevie you can get the paste and electrodes
- from the Grass Instrument company.
-
- The EEG response is pretty tiny - only a few microvolts. The
- amplifiers on the set-up to which I was connected had a gain of
- 10^4 and a frequency response of about .5 - 3000 Hz. I had to
- perform a task of trying to distinguish two slightly dissimilar
- current stimuli. The researchers were looking for specific
- cortical evoked potentials and also looked for what was hoped would
- be cellular responses by high pass filtering the resultant data.
-
- There diagnostic EEG tests taht look for certain well known evoked
- potential responses that occur at known latencies following the
- onset of a stimulus. An audio click stimulus can be used to
- generate a BSEP resonse. A trained technician can make neural
- diagnostic assesments by observing the BSEP. I suspect that
- diagnostic type EEG equipment may be much simpler than that used
- for research applications because a specific response is
- investigated.
-
- The other thing you want to watch out for is strict adherence with
- safety procedures when you go about wiring up people to devices.
- Battery powered amplifiers with optical or RF isolation are a good
- idea. Everything should be fused with fast acting very low mA
- fuses too.
-
- Joseph Carr has written several good books for do-it-yourself
- computer interfacing and biological projects.
-
-
- --
- Bill Mayhew NEOUCOM Computer Services Department
- Rootstown, OH 44272-9995 USA phone: 216-325-2511
- wtm@uhura.neoucom.edu (140.220.1.1) 146.580: N8WED
-