Neuropixels
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Hold and protect the Neuropixel probes
Neuropixels, the fancy new high-density neural electrical recording probes, are finally accessible by the neuroscience community at large! With “384 dual-band, low-noise recording channels that can individually be configured to simultaneously record AP (action potential) and LFP (local field potential) signals from 960 selectable, low-impedance TiN electrodes densely tiled along a 10-mm long, 70 x 24 µm cross-section straight shank”, it’s sure to get you more data than you really want!
There currently is no good method to hold the probes within a stereotaxic rig. There are expensive but inadequate commercial systems or vague DIY systems that attempt to fix this problem, but fall short of the mark. These current offerings do not well align the probe with the axis of the stereotaxic system (putting stress on and breaking probes), have no way of holding on to the headstage, offer no protection for the probes during soldering or storage, and don’t offer flexibility between acute and chronic systems.
Here is a design that can be microSLA printed (rigid nylon infused preferred) to more effectively hold the Neuropixel 1.0 probes and headstage. A protective cap is provided in this design, as well as a base to hold up to 6 probes/headstages at once. The design is expanded to allow for chronic implants as well. A future design will flatten space near the insertion points, allowing for several probes to be implanted at once.
Parts and Print Settings
The system given herein relies on screws to hold the probe in place (though you will find the fit so good it isn’t really necessary), hold the headstage on, and connect the chronic system to the stereotaxic rod. The threading through this plastic isn’t super strong and it is really just easier to glue a nut in place rather than tap into the plastic. Any old 5 minute epoxy is probably good enough for this purpose. The nuts are all M1 (McMaster 91828a003) and all screws are M1, 3 mm long screws (McMaster 91800a052). Anyone know of any source for similar screws that are not flathead? They’re a royal pain!
UPDATE: the kind folks at Plexon have pointed me to some M1 screws using a hex head. Check out the amazing neuroscience they produce. Thanks to them!!
The Stand holds onto up to six ProbeHolders with M3 screws (McMaster 90592a085) with associated M3 nuts (McMaster 92005a116), no glue or epoxy is necessary. It can be printed with an FDM printer in whatever material at high speed, low resolution settings. I’ll race you to see who can print it the fastest.
All other parts should be printed in a rigid microSLA. We observed great success in Nylon infused microSLA. Don’t have such a printer or material? Neither do we. We use Rosenberg Industries They have shown great success and are aware of ONE Core projects and requirements.
Files
Major update 26.Mar.2020.
| File | Description | Version | Probe |
|---|---|---|---|
| ProbeHolderNeuropixel.26Mar.ipt | ProbeHolder | Acute | Dovetail |
| ProbeHolderNeuropixel.26Mar.stl | ProbeHolder | Acute | Dovetail |
| ProbeHolderNeuropixel.ipt | ProbeHolder | Acute | Dovetail |
| ProbeHolderNeuropixel.stl | ProbeHolder | Acute | Dovetail |
| ProbeHolderNeuropixelFlat.ipt | ProbeHolder | Acute | Flat |
| ProbeHolderNeuropixelFlat.stl | ProbeHolder | Acute | Flat |
| ProbeHolderNeuropixelProtectiveCap.ipt | Protects the probe | Both | Both |
| ProbeHolderNeuropixelProtectiveCap.stl | Protects the probe | Both | Both |
| ProbeHolderNeuropixelStand.ipt | Holds 6 holders | Both | Both |
| ProbeHolderNeuropixelStand.stl | Holds 6 holders | Both | Both |
Note: you can view the file in your browser by clicking on the .stl link. You can then download the file with the down arrow box button. Editable .ipt files download directly with the ipt link.
Features, Use, and Updates
Features (as updated 26.Mar.2020):
- Holds the NP headstage and probe on a basic 8 mm diameter stereotaxic rod.
- Dovetail or flat design
- Design incorporates features for chronic (future-ish) or acute recordings
- Well holds the flex, ground wire, and headstage wire
- Ground and headstage wire exit out the top/back of the holder ensuring they are well secured
This design allows or will allow for use with both chronic or acute neuropixel recordings. As such, there are four stabilizing posts that can be affixed to the skull for chronic use. They have large bases and a roughened surface (blue) to better secure dental cement. If you are doing acute, the posts can be snapped/cut off at the weak points (circled in red). The front face can snap off in two places: the first removes the entire post and the second removes the chronic post but maintains the use of the protective cap (recommended).
This design also allows for removal of the NP probe out the back (blue arrow). Mainly intended for chronic, the probe holder can remain cemented to the skull, the holding screw can be loosened, and the NP probe can be removed out the back (hopefully without damage).
The probe snakes around the holder in an ‘S’ shape. There are several posts to hold the flex to keep it in place and away from the delicate probe.
Wire management has been a major issue for me. Here is a post to attach ground:
From a design from Guido Meijer at the Hardware Platform of the Champalimaud Centre for the Unknown, a square hole has been added that allows for a 90 degree header pin to be glued in place.
The post is now hollow. This allows you to put the ground and headstage wires in the post. Ground can exit straight through, and the headstage wires can exit on the side with the headstage.
The wires can exit out of the back of the post (red) and be attached to the holder with twisty ties or string (green).
Bending bare wire to solder ground to ref on the delicate flex was unnecessarily stressful for me. So on the back of the post, there are two holes at the same distance as the holes in the flex. So strip some wire bare, and use this ‘jig’ to bend the wire (green), then insert into the flex and solder.
The back of the post also allows this feature to bend bare wire. I think that this will bend wire such that it can solder the ref to ground and stick out to the side, allowing for an easy attachment point. I have not tested this yet (#COVID19), but it doesn’t cost us anything.
Assembly
You will find that the print holds the Dovetail probe well on its own, but it may be good to secure the probe against the holder anyhow. Simply glue an M1 nut into the top section here. Any old 5 minute epoxy will do. Try to get the epoxy on the sides of the nut and throw it in. Should you get epoxy in the threading, that is OK. Let it dry just a little before using a screw to clear the threads (drive it through multiple times).
Why are there more places for screws below? Well, we originally thought that people may want the probe really far back on the holder, and then…well, I’m too lazy to remove them.
On the other side you can see a feature that sits above the probe. This holds the probe during installation (should you miss the dovetail rails) and protects the probe if you over tighten the screw and pop the probe out. I have not seen that happen, and tried to make it happen but was unable to do so. Also, this feature holds the protective cap. So if you are using that, throw another nut with glue on the sides in here. Let the epoxy dry well.
Now you can grab your Neuropixel Probe and slide it in. You should be well able to hold onto the sides of the probe near the dovetail as you insert it. It may be best to now insert the probe into a headstage as it makes managing the flex cable a bit easier. Carefully snake the flex through the two bends as such:
The headstage is attached to the probe holder via two M1 screws. These holes are sufficient to simply self-tap the screw (that is, just screw it in). No good metal threading (A.K.A. nuts) is needed.
Install the protective cap by having it angled well away from the shank and hold it against the nut while you attach it with an M1 screw. Keep it ever so slightly loose so you can rotate it up over the probe, for maximum protection.
When the protective cap is above the probe, there are several features to ensure that the cap cannot fall on the probe. This includes the two faces below. The blue arrow points to a face that stops the cap from being rotated too far, and the red arrow points to the main face that ensures the cap does not fall on the probe.
The stand to hold several probe holders (which in turn hold the probes) can be assembled by simply dropping in the M3 nuts and screwing in the screws. The base provides a stable structure, but you can also attach the stand rigidly to a breadboard with the holes in the back. We even designed it for metric and imperial (holes marked with an I) breadboards!
You can now solder the reference to ground (recommended), attach ground to an external site, and otherwise handle your probe in a reckless fashion (ONE Core not responsible for any broken probes)!
No Dovetail (flat?)
Some people may have ordered the probes without dovetails (I think it is called a flat design?). These people are adventurous and crazy and generally my kind of people. As such, we also offer designs to allow for holding flat probes to these holders. It is the same design but without the dovetail cut out, offering a nice flat surface to which you can glue the probe. How do you ensure that the axis of the probe is the same as the axis of the stereotaxic rod (such that they move together)? I dunno. Eyeball it? With no other aligning surfaces for me to use, you’re on your own! But at least the curving flex kind of pushes you to the correct alignment, so you have that going for you, which is nice.
Future
A chronic implant system is mostly done, but not yet tested (any beta testers out there?). It weighs in at 1.26 grams (2.59 grams with the probe and headstage).
Some researchers can never have enough data and want to get multiple probes in the same area at the same time. This will require minimization of the space near the probe shank. A design for this is nearly complete.
We also have ideas for a commutator system. Anyone looking to collaborate?
ONE Core acknowledgement
Please acknowledge the ONE Core facility in your publications. An appropriate wording would be:
“The Optogenetics and Neural Engineering (ONE) Core at the University of Colorado School of Medicine provided engineering support for this research. The ONE Core is part of the NeuroTechnology Center, funded in part by the School of Medicine and by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under award number P30NS048154.”
