Massive electrode array will do first large-scale recording of brain activity | Hacker News Reader

Massive electrode array will do first large-scale recording of brain activity

kurzweilai.net

33 pointsrpm432110 comments

This isn't the first array of this type; it isn't even the tenth. There are two major commercially available systems. Neuronexus is based on printed circuits and is used mostly in rodents. The Utah array is micromachined and more robustly packaged, and is used mostly in monkeys and some humans.

http://neuronexus.com/products/neural-probes http://www.blackrockmicro.com

This will be the first of this scale. On both those sites the most channels I could find was 64. This program is planning 10.000 channels for unprecedented resolution and scale.

Since 16 channels is enough to predict if a subject is looking at a face or not, it is exciting to research what this large-scale system is going to be capable of. Next to neuroscience, it could help with healthcare (research into dementia, epilepsy and schizophrenia).

The article wasn't clear on this, what is a "channel" in this sense? What is actually measured, from a physical perspective?

A "channel" usually means an individual contact on the device from which you can record a signal. A single channel may record "spikes" (action potentials) from dozens of neurons, but of those typically only 0-3 are distinguishable, depending on how close the electrode is to the neurons and how close the spike shapes are to each other. With ordinary metal electrodes, one can usually isolate action potentials from an average of 1-1.5 neurons per electrode.

However, not all channels are created equal. High channel count arrays typically have high contact densities. If the contacts are very close to each other (<100 microns or so), adjacent channels may record signals from the same neurons. I'm not entirely sure how this will affect the actual number of neurons one can isolate, but I'm eager to see. The contacts will record signals from fewer neurons than if the density were lower, but the increased density may make it possible to isolate signals that would otherwise be lost to noise, and will certainly make the process of determining which action potentials came from which neurons simpler.

The NeuroNexus Matrix array can be configured with up to 256 contacts. It's basically a Utah-style array with many shanks arranged in a rectangular grid. The difference from the standard Blackrock Utah array is that each of those shanks has multiple contacts along it. This is their newest product and you can buy it now, although I have no idea how well it actually works.

This technology is in principle extensible to much larger channel counts, if you increase the size of the array, the density of the shanks, and/or the density of the recording sites along each shank. I know that the Boyden lab at MIT has been working on this with the goal of simultaneously recording from >1000 sites. I'm not sure if they've met that goal yet, but they've been presenting on their progress at the annual Society for Neuroscience meeting since at least 2012.

One problem with standard microelectrode array technology is that it only works for targeting a small proportion of brain areas. You can only record from regions on the surface of the brain. Structures in sulci (folds) are difficult to reach because you'd have to pull apart the sulcus to insert the array, and many sulci contain blood vessels that will be ruptured if you do that. Targeting deeper structures like the thalamus (probably the most interesting target for schizophrenia) is intractable with this technology at least in primate brains because the electrode shanks have to penetrate a couple centimeters into the brain. Even if you could engineer an array with long enough shanks and manage to insert it without destroying it, you might do so much damage to brain tissue between the surface and the target that the resulting data would not reflect normal brain function.

I used to work in a lab that did some single-neuron recording and some array-recording. We recorded from monkeys. The monkeys had to have a chamber surgery in order for electrodes to be inserted into the brain.

This article mentions that they'll be recording from many areas simultaneously. I would think this would mean multiple chamber surgeries in different areas.

I know that these surgeries do damage to the monkeys. Could a monkey sustain so many chamber surgeries? What about other animals?

Usually multi-shank arrays like the one depicted in the press release are chronic, so no chamber is necessary. Instead, they are implanted directly into the brain during surgery and wired to a port on the animal's head. There's still some risk, since one still has to remove the skull above the target site and also cut and resew the dura mater, but the skin can be sewed back together after implantation and the bone will eventually regenerate. Unlike in an acute preparation with a chamber, there is no exposed dura that needs to be cleaned regularly to prevent infection, and the electrodes are inserted just once instead of repeatedly.

If the recording contacts are sufficiently dense, the total area of skull that needs to be removed to implant 1000 channels worth of arrays may actually be less than in a conventional two-chamber (maybe even single chamber) acute primate preparation. But we'll see.

Very interesting, thanks for the explanation!

The OP's point about damage still holds. After implanting the chronic arrays you have to wait about 3 weeks before recording (the area is silent). It is assumed that the responses are normal after that - and it seems so. But we have a lot of results from arrays that have no counterpart from single electrode recordings so we really don't know.

You are basically jamming a pincushion into the cortex. Trauma is inevitable. The denser the array the more the damage (the more mass you are jamming into cortex). You most likely have a perturbed cortex that has recovered from damage.

Is this the same as original intact cortex?

Yes, the typical caveats of putting things in the brain still apply. But I'm expecting that the increased density in these arrays will come mostly from putting multiple contacts on each shank rather than putting the shanks closer together, which may not produce any more damage than an ordinary Blackrock array.

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