Our research goal is to better understand the neural mechanisms underlying memory processing, especially to examine the interactions between specific brain regions in real-time during different learning time points and also during sleep. In this regard, here we developed a novel drive implant that enables us to look at neural activity simultaneously across multiple brain regions in freely moving rats during task and rest periods. To record brain activity in behaving animals, researchers commonly use self-made complex implants with dozens of individually movable wire electrodes.
However, using and implanting these devices successfully can take years of training. Our drive is easy to build and does not need expert hands, making this kind of research more accessible. The TD drive was designed based on three ideas, contrasting it to other complex designs.
It should allow for recording of multiple brain areas bilaterally, be relatively easy and quick to build, and researchers should be able to adapt the design themselves without having to have advanced knowledge of 3D design. We aim to understand how do different brain regions interact with each other when rodents perform simple versus complex behavior tasks. How does learning and different drugs affect these interactions between brain regions during sleep, and how are these interactions during sleep related to memory performance?
To begin, create the 3D models. Click on Upload to open the drive body design in the Autodesk Fusion software. Under the Modify tab, click on Change Parameters.
Adjust the coordinates for the first recording location by entering the anteroposterior coordinate in anteroposteriorSite1, and the mediolateral coordinate in mediolateralSite1 and press OK.On the 3D printed model, use an M1 tap to tap the guide holes for the shuttle screws, which are the extension of the counter sink holes. Then slide a 3D-printed shuttle onto an M1 by 16 screw and use an M1 brass insert to hold the 3D-printed shuttle in place. Using a small amount of soldering paste, solder the brass insert to the screw.
After the shuttle assembly is cooled down, gently rotate the 3D-printed shuttle multiple times around the screw. Next, to assemble the drive, cut commercially available polyimide tubes to approximately 25 millimeters in length. Insert the polyimide guide tubes into the drive body and finalize the insertion using tweezers.
Using a thin needle or toothpick, apply a small amount of liquid cyanoacrylate glue to the holes at the top of the drive body to fix the guide tubes in place. Also, apply cyanoacrylate glue to the interface between the guide tubes and the guide stencil at the bottom of the drive body. Cut the polyimide guide tubes on the bottom such that they extend approximately 1 millimeter beyond the center pedestals of the drive body.
Insert two shuttle assemblies in the drive body. Screw the electrode interface board to the drive body with M2.5 x 5 polyamide screws. Then insert a stainless steel M2 nut into the extrusion on the left cap half and fix it with cyanoacrylate glue.
Tap the hole on the front of the right cap half with an M1 tap. Next, prepare two metal plates as the surface for creating the electrode wire bundles. Attach plotting paper to the first plate and knot two sticky painter's tape onto the second plate with the sticky surface pointing up.
Draw a clear line with an angle of 60 degrees on the plotting paper. For each electrode bundle, cut the electrode wire into the required number of pieces with the specified length. Gently pick up the four wires by touching them with a fingertip and place them as close as possible next to each other on the painter's tape.
Under a microscope, use fingers or forceps to place the wires together as close as possible. Apply a thin layer of liquid cyanoacrylate glue to the first two centimeters of the top of the bundle. After the setup dries fully, remove the wire bundle from the tape and transfer it to the plate with the plotting paper.
For the retrosplenial cortex bundles, make a straight cut at the bottom of the array. For the hippocampus electrode bundles, place the array on the plotting paper such that it intersects the 60 degree line. Then use the line as a guide to make a cut at an angle of 60 degrees to the direction of the wires.
Then using a razor or scalpel blade, carefully split the shortest of the four wires cutting perpendicular to the wire direction. For the prefrontal cortex bundles, split the bottom of the array into two two-wire bundles. Shorten one of the two wire bundles by 1 millimeter by cutting it perpendicular to the wire direction.
Then cut two pieces of 6-centimeter length for the ground wire. Also cut eight pieces of 6-centimeters length for the electroencephalogram wire. Next, place an M1 x 3 stainless steel screw in a third hand.
Wrap the deinsulated side of the ground or electroencephalogram wire around the shank of the screw. Apply a small amount of solder flux and solder the wire to the screw. Place a sip dip pin in the third hand so that the female side is accessible.
Insert the deinsulated part of the opposite side of the wire into the sip dip pin and solder the wire to the pin. Next, place another sip dip pin in the holder with the male side accessible. Solder the deinsulated side of the other wire to the male side of the pin.
Use a multimeter to verify that there is a continuous connection between the screw and the deinsulated wire end of the wire pin assembly when both assemblies are connected. To load the wire bundles into the drive, attach the drive to a holder. Once the drive body is stable, carefully slide one of the wire bundles into the respective polyimide tube.
Use thin forceps to grab one of the wires and carefully bend it towards the desired hole and insert it. Once inserted, use a gold pin to pin it into the electrocorticography hole. Next, when the fixed wire arrays are aligned, apply a small amount of strong epoxy glue to the top of the guide tubes to fix the bundles in place.
To fix the movable hippocampus wire arrays, first move the shuttle to the highest required position. Then push the wire bundles into the U-shaped opening of the shuttle and glue them in place with a small amount of a strong epoxy glue. Carefully insert the open end of the wire pin assembly of a ground wire through one of the through holes marked ground and fix it using a gold pin.
Remove the drive from the holder. Take care not to bend any of the wire assemblies. To recover the electrode interface board after experimentation, gently push soft tweezers between the board and the drive body, or carefully lift the EIB by hand to release the remaining cyanoacrylate bond.
The TD drive was implanted into eight rats for a pilot run, and implant surgeries were carried out two weeks post arrival. Post-surgery, animals showed adaptability to the implants with fixed electrodes in frontal and retrosplenial regions, and adjustable hippocampal bundles to enhance signal coverage. Sleep recordings were performed on tethered rats in a recording box.
While wake data was recorded as wireless recordings in a larger maze. In seven out of eight animals, all target sites were reached on at least one hemisphere. While some animals began to lose their implants after two months, most retained them for up to 100 days.
During this time, the local field potential remained stable as observed by delta oscillations in the hippocampal channel.
