Are large numbers of channels superior to smaller numbers ? [resolved]

edited September 7 in General Discussion

Hey,
I'm trying to build a neurofeedback setup in order to attempt to treat my mental health (there is no neurofeedback facility in my country). So far I have only found a 128-channel 10-5 system cap in china for 120 usd, which is quite good price. I'll be able to use it even with lower amount of electrodes.

So far I don't know how many electrodes do I need, so I'm thinking why not the highest number 128 channel? However, after browsing for a bit, looks like diy people don't build 128 channel eeg setups?
This EEG-SMT looks like it's only for 5 electrodes https://www.olimex.com/Products/EEG/OpenEEG/EEG-SMT/open-source-hardware
Here is 24 channel but price is above high https://www.alibaba.com/product-detail/New-EEG-Trolley-Machine-with-eeg_60599438069.html?spm=a2700.galleryofferlist.normal_offer.d_title.38c4ee99USWoJy

Where is the 128 channel eeg amplifier, so that I would have support for max number even if I later turn out to decide to use less electrodes?
And why would it be so expensive, shouldn't it be like a relatively simple device for electrical engineers who understand the mechanism? iPhone seems way more complex and it's cheaper than some of those 24 channel eeg amplifiers

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Hi Dirigent,

    Neurofeedback is commonly done in clinics with only 2 or 4 channels. And is quite effective. So you do not need high channel counts. Another clinical setup that is relatively common, uses a 19 channel amp and cap for 'assessment' / QEEG. Then typically drops back to just a few channels for the training. A good middle ground is Pete Van Deusen's Brain-Trainer system, which uses a 19 channel cap for assessment, but only needs to sample 4 channels at a time. Aided with a switch-box in the amp that does the electrode changing with a single action. The same cap can be used for training, which uses all 4 channels simultaneously.

    Pete's system can run with the OpenBCI Cyton (8 or 16 channels) and Ganglion (4 channels).

    There are many other neurofeedback posts, visible using the Google Advanced Search button in the upper right column.

    A major disadvantage of high channel count systems, is the setup time to gel the cap and get all channels operating solidly. Even with 19 channels this can take 10+ or more minutes. I would not be surprised that 32, 64 or 128 channels would take multiple times that. Most likely scaling linearly.

    Regards, William

  • edited September 4

    @wjcroft regarding your mention of wet electrodes, yeah, but I saw there are dry electrodes? Are they usable?
    If for assessment they use 19 channel qeeg, why is there 32, 64, 128, 256 channel eeg?
    Also I don't comprehend why can't there be a one cheap 128 channel amplifier that would fit all of the needs for higher, lower amount of channels.

  • wjcroftwjcroft Mount Shasta, CA

    @dirigent said:
    @wjcroft regarding your mention of wet electrodes, yeah, but I saw there are dry electrodes? Are they usable?

    The Ultracortex headset in the shop, used with Cyton is 8 or 16 channels dry passive. And can also be configured with dry active electrodes. In some applications such as QEEG or ERP / P300 / VEP, wet electrodes generally perform better. Since all QEEG databases were constructed with wet passive caps, it makes for maximum accuracy to continue to use wet.

    If for assessment they use 19 channel qeeg, why is there 32, 64, 128, 256 channel eeg?

    Higher channel counts are primarily used for detailed neuroscience research projects, and for increased voxel resolution of source localization algorithms.

    Also I don't comprehend why can't there be a one cheap 128 channel amplifier that would fit all of the needs for higher, lower amount of channels.

    As mentioned, much clinical and home-training neurofeedback happens with only a handful of channels. And generally does not benefit from large / huge channel counts, because of setup / cleanup considerations.

    Regards, William

  • @wjcroft what kind for cleanup consideration, if dry electrodes are used?
    also have other question... https://openbci.com/forum/index.php?p=/discussion/3107/cyton-raw-materials-cost/p1?new=1

  • wjcroftwjcroft Mount Shasta, CA

    The dry electrode headsets, bands, caps, have much easier setup and no cleanup time.

  • wjcroftwjcroft Mount Shasta, CA

    This tutorial video shows how to place cup electrodes using paste on the scalp. Without needing a cap or the gel that they require. If only placing 2, 4, etc. electrodes, plus reference and ground -- this is straightforward to do.

    https://openbci.com/forum/index.php?p=/discussion/176/placing-electrode-sensors-on-the-scalp

  • wjcroftwjcroft Mount Shasta, CA

    One other type of cap / system in use, is based on 'saline' (dissolved salt) solution, used instead of the messy 'gel' used in conventional EEG caps. So there is no clean-up time involved, AND you get the benefit of somewhat better signal quality, since this is still wet electrolyte based. This page shows a range of commercial saline systems.

    https://sites.google.com/site/biofeedbackpages/velcro-saline-sensors/commercial-saline-sensors

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