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.
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.