electrode placement for alpha, 1 or 2 grounds?
Hello guys, I have some questions about the number of electrodes and its position in the head.
for a simple test I use this configuration:
- 2 electrodes in lobehears shortcircuited, as reference.
- 1 electrode in forehead, as right leg driver (for noise cancel)
- 1 electrode in Occipital to detect alpha waves with closed eyes.
questions:
- is this configuration correct??
- Do I need an extra electrode for GROUND (I read it in "hackathon guide")??
- if I need the "GROUND" electrode, where do I connect it??
thanks!!
for a simple test I use this configuration:
- 2 electrodes in lobehears shortcircuited, as reference.
- 1 electrode in forehead, as right leg driver (for noise cancel)
- 1 electrode in Occipital to detect alpha waves with closed eyes.
questions:
- is this configuration correct??
- Do I need an extra electrode for GROUND (I read it in "hackathon guide")??
- if I need the "GROUND" electrode, where do I connect it??
thanks!!
Comments
I'm planning to test the alpha wave next week so I don't have much experience. I believe you don't need that much of electrodes though. @Chip demonstrated an alpha wave detection system with only two electrode here at
http://eeghacker.blogspot.com/2013/11/openbci-alpha-wave-detector.html
also, I´m using a bipolar supply (+/-2.5V), and i´m trying to use the RLD for conceling noise.
I´ll check the link, thanks!!
eegexplore.blogspot.com
Do you have any blog, sharing or publishcation about your work?
my email is: [email protected]
Great discussion!
An EEG records the difference in voltage between one electrode and the reference electrode. Often, this is all you need.
Most EEG systems often include a third electrode, which can go by a variety of names: ground, driven ground, driven right light, or bias. The ADS1299 terminology is "bias". This connection helps reduce noise and it helps keep your body's DC voltage level in-line with what the ADS1299 needs in order to properly amplify and digitize your EEG signal. Without the bias line connected to your body, your EEG signal (as seen by the ADS1299 chip) might start floating off and, eventually, saturate the input.
So, if you're looking for the simplest setup, put your sense electrode on the back of the head (the Occipital area) and put your reference electrode on your earlobe or on your forehead (for eyes-closed Alpha, it doesn't matter). If you get a good signal, you win!
If it doesn't work, you can try putting your bias electrode on your other earlobe. Maybe that'll make it work. If not, you've got other problems with your system or your setup.
Eyes-closed alpha is definitely a good place to start. An even better place to start, though, is with measuring your ECG (your heart pulses) because those signals are very large...http://eeghacker.blogspot.com/search/label/ECG
Good luck! And let us know how it works out!
Chip
- positive electrode: O4
- Negative electrode: Cz
- Bias electrode: Lobehear
and these are my results:
https://drive.google.com/file/d/0BwR99SVSDTjdTkhncXg2NzZxLVk/edit?usp=sharing
https://drive.google.com/file/d/0BwR99SVSDTjddnI3cGk2czFKeTg/edit?usp=sharing
sorry I don't know how to post it in this page.
You can upload images into your comment posts here, using the icon above the text area, looks like a small TV screen. (Hover over that icon, it will say "Insert Image"). It expects an URL.
Your 10 hz alpha looks good, about 3 uV amplitude on the spectrum graph. Many people interested in EEG activity above say .5 hz, will run their signal through a digital highpass filter before graphing it. That would drop off your DC component and the ~ 1hz overlay that is on top of your alpha in the graph.
Congrats on getting the TI dev kit board to work. I've heard it's not always that easy (a lot of components to wrestle.)
William
Congratulations! Your data looks great!