February 6, 2015
NeuroNexus has developed a true 3-dimensional probe, the Matrix Array. The Matrix Array is a silicon-based probe that has a 2-dimensional array of shanks in the X-Y plane, and each shank has multiple recording sites aligned vertically on a Z-axis. The Matrix Array, then, allows for recording volumes of tissues that include multiple neural layers as well as multiple columns.
Figure 1: (Left) Render of 3D nature of the Matrix Array. Multiple 2D probes (in this example, spanning 1400 µm along z-axis and 1200 µm on x-axis) are stacked to span 1800 µm in the y-axis. The stacking spacing can be adjusted to span 600 µm or 3000 µm in the y-axis, and different 2D probes can be selected to span different recording areas in the x-axis and z-axis. (Right) Photograph of a Matrix Array. The small white circles along each shank are the recording sites.
These blog posts describe some of the developmental process of the Matrix Array, and the testing that we have done to ensure that it is a high quality product. Matrix Arrays have been field tested in various areas of the cortex of non-human primates at five independent research institutions. In our last blog entry we reported some of the developments in our Matrix Array insertion procedures that were tested and re-designed based upon work done in labs in Michigan and Texas. Today, we’ll focus on the progress of the recording tests that have been done to date.
In the spring of 2014 a lab in Illinois implanted a 128-channel Matrix Array into the primary motor cortex. The array was comprised of four 32-channel (M4x8-2mm-200-400-703: four shanks, eight sites per shank, 2 mm long shanks, 200 µm site spacing, 400 µm shank spacing, 703 µm2 site area) arrays spaced 1000 µm apart. The experiment lasted for two months, during which they recorded spontaneous activity during periods of rest and examined the power spectral density. This experiment was reported on a poster at the Neural Interfaces Conference in June, 2014.
Figure 2: Neural Recordings from the primary motor cortex of a non-human primate. (Left) Sample of recorded waveforms from a bank of 32 electrode contacts (t = 28 days post-implant). (Right) The number of tracked single units from the same bank of 32 electrode contacts over the first month.
Two labs are currently recording from Matrix Array Implants performed in October of 2014. One lab, in Maryland, implanted a 128-channel Matrix Array comprised of four 32-channel M4x8-2mm-200-400-703 probes, spaced 1000 µm apart. They are recording both LFP and single unit data.
A third lab, also in Illinois, implanted two 128-channel Matrix Arrays (256 channels total). Both arrays had one 32-channel array that was longer (M4x8-5mm-150-200-703, 5 mm long with 150 µm site spacing, 200 µm shank spacing, site size 703 µm2) for recording in a sulcus. The other three 32-channel arrays that comprised each Matrix Array were M4x8-2mm-200-400-703 arrays. The 32-channel arrays were spaced 600 µm apart.
Figure 3: Matrix Array implanted into Area 2 and Area 3a of cortex, with cortical landmarks, arrays, and array banks labeled (anterior is to the right of the image).
At the time of this blog, both experiments have surpassed the 3-month mark. In the words of the second lab from Illinois, “Our implants have been consistently picking up neurons for the past three months, in both Area 2 and 3a. The arrays seem to have lasted much longer than other similar multi-contact electrode arrays we've had experience with, including LMAs and Michigan probes, so the Matrix array is promising for a few experiments we've wanted to conduct in cortical areas that lie deep in a sulcus, like the Area 3a experiments we've been collecting data for with this implant.”
Figure 4: Composite image of recordings taken from each bank of the two 128-channel Matrix Arrays (256 channels total) implanted into Area 2 and Area 3a, labeled in the same way as in Figure 3.
Close-up detail, Insertion methods, and more
A true 3D neural interface, for both acute and chronic experiments.