August 31, 2016
The Matrix Array is the result of years of research, collaboration, and development. In this video, we demonstrate our computer-controlled insertion technique with a 5 mm Matrix Array.
March 2, 2016
In collaboration with Rogue Research, NeuroNexus is offering an opportunity for a hands-on in vivo surgical training with the Matrix Array three-dimensional probe and Vector Array 70 mm deep brain probe using live macaque models. The workshop will take place in Montreal (6/8 – 6/9), and covers a wide range of topics including surgical planning, navigation, implantation, electrode design, and data acquisition & analysis.
Observation is free; You may reserve a brain hemisphere to perform and mimic a realistic surgery specific to your research area for $3,500. NeuroNexus will provide a SmartBox to collect any potential pilot data.
The training course will cover:
- Precisely targeting areas of interest using advanced imaging techniques (CT & MRI) and surgical navigation tools
- 3D skull reconstruction, brain reconstruction, superimposing or merging of imagery data sets, and implementation of data into stereotactic coordinate systems
- Visualization of cranial real-estate for electrodes, microdrives, headholders in 3D space
- NeuroNexus thin-film electrodes and Matrix Array designs
- Using Matrix Arrays
- Hands on training and implantation of the Matrix Array (1 hemisphere per group)
- Training with the NeuroNexus computer-controlled insertion tool
- Data acquisition and analysis
- Collecting additional neural and behavioral data post workshop (Additional fees may apply. Contact us for more details.)
Space is limited. The workshop can accommodate up to 6 groups, with up to 3 participants per group. You are responsible for travel and 1 night of stay in Montreal; Free housing is available. If interested, please register by May 27th, 2016.
September 15, 2014
NeuroNexus has developed a true 3-dimensional probe, the Matrix Array. The Matrix Array is a silicon-based probe assembly that is comprised of an array of shanks aligned along a single lateral plane, with each shank containing multiple electrodes vertically positioned. The Matrix Array, then, allows for recording volumes that span both cortical layers and cortical columns. These blog posts will 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. Today, we’ll focus on the methods for implanting the Matrix Array.
Traditional NeuroNexus probes have either a single shank or multiple shanks that are all positioned in the same plane. Thus, insertion of those probes is fairly straight forward. However, probes with a 2-dimensional array of shanks come with special insertion challenges. Depending on how close the shanks are to each other, it is possible to get a “pincushion effect,” in which the penetration of one shank is hindered by tissue dimpling caused by a different shank. (This happened to me with a probe that I was attempting to use during my first postdoc to record in the dorsal root ganglia, and the shanks of the probe bent instead of inserting, ruining the probe.) One way to overcome this effect is to insert the probe with a lot of force, and this is a method that is often used to insert probes with this shape profile. However, high-force insertion can cause tissue damage that manifests in longer healing times, longer periods before recordings can be taken, or possible neural damage. Thus, we spent some time developing and testing alternate insertion methods for the Matrix Array.
The shanks of the Matrix array are thicker (50 µm) than the standard NeuroNexus probe (15 µm). This increased thickness makes the shanks stronger and able to cleanly penetrate tissue. The shanks are still thin enough, however, that the ratio of space between shanks to shank thickness still prevents the pincushion effect. Thus, we are able to do controlled insertion of the Matrix Array without requiring a great deal of force. Finally, we chose a computer-controlled insertion motor with extremely fine step resolution (0.05 µm/step) and speed resolution (0.22 µm/sec).
We first tested our insertion method on models, such as plastic wrap over agar. Once thoroughly tested in that way, we moved onto in vivo testing and eventually implantations with our beta testers.
One such test was done in the lab of researchers in Texas in October of 2013 (pictured above). The surgery was performed by our collaborators, implanting the Matrix Array into the motor cortex of a rhesus macaque monkey. The Matrix Array is held onto the tip of the IST-Motor insertion tool by vacuum. Using a craniotomy 1.6 cm in diameter, we fully inserted the 0.75 mm probe, in increments of 0.2 mm every 30 s. Once satisfied that the probe was completely inserted we turned off the vacuum and withdrew the insertion tool, leaving the probe in the brain. During this experiment we held forceps on the back of the inserted Matrix Array to make sure that it remained in place, but in prior and subsequent tests the forceps were not necessary. At this point, the probe was successfully inserted.
The insertion process is but one step on the path to having successful 3-dimensional recordings, and it perhaps is not even the first step that one might think of. But it is an important step nonetheless, and we made sure to develop a good approach and fully test it to ensure that the Matrix Array provides maximum benefit with minimal energy.
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.