User s manual for the SC32 and SC96 form-fitting recording chamber and microdrive systems

Transcription

1 User s manual for the SC32 and SC96 form-fitting recording chamber and microdrive systems 1. Description of the chamber system Description of the microdrive system Phase I - Chamber implantation Phase II Craniotomy Phase III - Microdrive implantation Advancing electrodes and recording neural activity

2 Form-Fitting Chamber System Figure 1. Exploded view of the form-fitting recording chamber system. The form-fitting chamber (Fig.1) provides hermetically sealed access to the brain. Its bottom surface matches the top surface of the cranial bone at a specific site. It contains an internal plug with a bottom surface that matches the inside surface of the cranial bone. A silicone o-ring rests in a trough on the top of the chamber wall. When the protective cap is tightened the plug compresses the o- ring and provides a water-tight seal. The chamber system is made in two sizes (small and large) which couple to the GMR microdrive systems (SC32 and SC96). 2

3 Parts List RC-F-L-Ti Figure 2. Form-fitting chamber components list. Item# Description Quantity/System 1. Chamber 1 2. Form-Fitting Plug 2 3. Short Plug 2 4. Chamber Cap 2 5. Removal Tool 1 6. O-ring 5 3

4 Form-Fitting Microdrive System (SC96-32mm) The form-fitting microdrive system (Fig.3) is designed to be semi-chronically implanted within a form-fitting chamber and provide independent control of multiple microelectrodes. Electrode movement is controlled by a precision lead screw and the electrical signals pass through a printed circuit board (PCB) thereby avoiding loose wires. The actuators are spaced at 1.5 mm intervals. Electrode travel distances include 16, 32 and 42 mm versions. Movement resolution is 125 μm/turn of the lead screw. A silicone o-ring, provides a water-tight seal. Bone cement is applied to reinforce the implant and provide impact resistance. The microdrive system incorporates 32 (SC32) or 96 (SC96) electrodes. Figure 3. Exploded view of the SC96. Actuators, including the lead screw, compression spring, shuttle and electrode, are not shown. 4

5 Figure 4. Parts List SC96 Item# Description Quantity 1. Jumper cable (optional) 3 2. Actuator block 1 3. Screw guide 1 4. Ground connector 3 5. Printed Circuit Board (PCB) 1 6. Precision screwdriver 3 7. Protective cap 1 8. Lead screw Compression spring 100 Item# Description Quantity 10. Shuttle x 0.25" unm screw x 0.375" unm screw Retaining cap Polyimide tubing x 3/32 hex cap screw Hex Driver (1.3 x 40 not shown) Screwdriver (1.5 x 40, not shown) Holder (not shown) 1 5

6 Assembled Chamber and Microdrive Systems Figure 5. Multiple views of an assembled form-fitting chamber and microdrive system (SC96). 6

7 Phase I chamber implantation Figure 6. MRI-based skull model with stereotaxic coordinates marked by a point and the chamber outline marked with a circle. 7

8 Phase I chamber implantation Figure 7. Once the appropriate chamber location is identified, holes can be drilled for anchoring bone screws (#44 drill,.086 diameter). It s extremely important to use a sufficient number of bone screws to provide resistance to impacts. Holes for 14 screw holes are shown here. 8

9 Phase I chamber implantation Figure 8. Bone screws are then screwed into each hole. (Inset: GMR bone screw, 5.1 mm thread length.) It s extremely important to use a sufficient number of bone screws to provide resistance to impacts. 14 screws are shown here. 9

10 Phase I chamber implantation Figure 9. Position the chamber using the stereotaxic chamber holder mounted onto a coarse manipulator on the stereotaxic system. Inset: Exploded and assembled views of the stereotaxic chamber holder. 10

11 Figure 10. Photographs of a Rhesus skull in a stereotaxic frame, illustrating the use of the stereotaxic chamber holder. 11

12 Phase I chamber implantation Metabond Essential items: S371 (Catalyst), S398 (Quick Base), S399 (L-Powder), S387 (Mixing dish) Figure 11. A thin bead of Metabond bone cement (yellow) should be applied, using a 1 cc syringe with a blunt 18 ga needle. This will seal the interface between the chamber wall and the bone. The cement can be extended to some of the bone screws to provide an anchor. 12

13 Phase I chamber implantation Zimmer Osteobond Copolymer Bone Cement Cat. No Figure 12. Once the Metabond is cured a thin layer of bone cement can be applied to link the chamber to the bone screws. The cement should be applied using a 1 cc syringe with a blunt 18 ga needle. It is very important at this stage that the bone be dry and free of blood. This initial layer provides a key barrier to infection for the duration of the implant. 13

14 Phase I chamber implantation Figure 13. Once the cement has cured the stereotaxic chamber holder can be removed. 14

15 Phase I chamber implantation Figure 14. Additional layers of bone cement should be applied to complete the coverage of the screws. The cement should flow into all of the grooves of the chamber and extend to the underside of the flange on the chamber. All of the outer borders of the bone cement should be as smooth and continuous as possible. 15

16 Phase I chamber implantation Figure 15. Exploded view illustrating the placement of the o-ring, short plug and cap. Before placing the plug and cap, the chamber cavity should be thoroughly and repeatedly rinsed with a 4:1 solution of sterile saline and Betadine, followed by sterile saline, and then suctioned dry. 16

17 Phase I completed chamber implanted hermetically sealed cranial bone intact Figure 16. The chamber cap is installed as the final step. At this stage the chamber interior should not require cleaning. Any opening of the chamber should be done under strictly sterile conditions. Whenever the cap, plug and o-ring are removed they should be replaced with identical sterile parts. 17

18 Phase I completed chamber implanted hermetically sealed cranial bone intact Figure 17. Cutaway view of the installed chamber system. The cranial bone inside the chamber remains intact. The dural membrane is shown in blue. 18

19 Phase II craniotomy hermetically sealed Love-Kerrison Rongeur love-kerrison-punch-6-fwd- 3mm-thin-foot-plate.html Figure 18. A craniotomy is performed within the interior of the chamber. A starter hole can be made in the center of the chamber using a bone drill and all of the remaining bone should be removed using a pair of Kerrison Rongeurs (3 mm cutting width, 45 deg angle). 19

20 Phase II completed craniotomy completed hermetically sealed Figure 19. Installation of the form-fitting plug, o-ring and chamber cap. This step reseals the craniotomy, eliminates herniation and provides a hermetic seal. Inset: The bottom surface of the plug flange contains a small centering pin that should be aligned with a corresponding hole on the top surface of the chamber. Failure to do this could damage the dural membrane and prevent the cap from fully seating. 20

21 Phase III implantation of microdrive Figure 20. Exploded view of the assembled microdrive (SC96) positioned above the chamber. The microdrive also contains a centering pin on the underside of the flange. This must be properly aligned with the hole on the chamber wall. 21

22 Phase III implantation of microdrive Figure 21. The microdrive (SC96) is mounted within the chamber and fixed in place by tightening the retaining cap onto the chamber. This fit should be snug. Failure to align the pin or adequately tighten the retaining cap can lead to movement of the microdrive within the chamber. 22

23 Phase III implantation of microdrive Figure 22. An additional layer of bone cement must be applied to reinforce the microdrive. The cement should reach to the underside of the flange on the retaining cap. Keep the threads on the retaining cap free of any cement. 23

24 Phase III completed Fixation screw Figure 23. Fully assembled system with protective cap. Avoid over tightening the fixation screws on the chamber and never use set screws. They can easily strip. 24

25 Phase III completed Figure 24. Cutaway view of the fully assembled chamber and microdrive system. 25

26 Advancing Electrodes and Recording Neural Activity Figure 25. Cross-section of the lower end of the microdrive illustrating a row of microelectrodes in their respective guide holes. Each guide hole is back filled with sterile silicone grease (purple). Several layers of silicone sealant ( mm thick) are applied to the bottom surface of the microdrive (green). The dural membrane is shown in blue, microelectrodes in black. The starting position of each electrode tip is retracted 1.5 mm from the bottom surface of the drive. To enter the brain the electrode must be advanced through the grease, the sealant, and the dura. 26

27 Advancing Electrodes and Recording Neural Activity Figure 26. Photograph of the sealed bottom surface of an SC96 with glass-coated Tungsten electrodes advanced through the sealant by approximately 5mm. 27

28 Advancing Electrodes and Recording Neural Activity Each electrode tip is retracted 1.5 mm inside the bottom surface of the microdrive. One rotation of the lead screw causes 125 μm of movement of the electrode. (8 turns/mm) The electrode is advanced by counterclockwise rotation of the lead screw. The silicone sealant on the bottom surface of the microdrive is ~ mm thick. To make electrical contact with the animal it is necessary to advance the electrode by ~ mm. Additional electrode movement of ~1-3 mm will be required to pass through the dura and detect neural activity. The recommended sequence for the initial advancement of the electrodes is.. 1) Choose one electrode to work with initially. 2) Advance the electrode 4 turns at a time until you ve reached ~2.0 mm depth. Remove the screwdriver at 0.5 mm intervals to check the signal. Whenever the screwdriver is making contact with the leadscrew the signal will be very noisy. 3) Advance the electrode in steps of 1 full turn, again checking the signal after each movement. Additional information can be obtained by measuring the impedance of the electrode. Impedance values >2.5 MOhm indicate problems with electrical continuity. Impedance values <0.1 MOhm indicate a broken electrode tip. If this occurs the electrode should not be moved any further because the tip is likely to be bent and further movement into the cortex will damage the tissue. Impedance can be measured from the corresponding pin on the connector or by contacting the head of the lead screw on each channel with a fine probe on your meter. You should make electrical contact with the animal after ~2.0 mm (i.e. pass through the silicone sealant). After this the signal will likely get noisier as you advance through the dura. Once the electrode pops through the dura you should be able to see a clear local field potential and spiking activity as you advance into the cortical surface. Use grounded shielding if 60Hz noise is a problem. 28

29 Advancing Electrodes and Recording Neural Activity The dura is likely to dimple by a variable amount (~ mm) as the electrode passes through the tough membrane. This can lead to a recoil of the dura after the electrode pops through or to a sustained dimpling that gradually recovers over time. It s very difficult to know the details of this without being able to see what s happening. So there is some guesswork involved. A good rule of thumb is to assume that the dura will recoil and this will leave the electrode tip at a position deeper than the surface of the cortex once the recording has stabilized. To correct for this, you can slowly retract the electrode in 1/2 turn increments until the unit activity disappears. When this occurs that position can be considered as the surface of the cortex. Also, if a given electrode happens to be located above a sulcus, then it might take many mm of travel before the electrode tip passes into cortex and you detect unit activity. Be sure to keep accurate records of the number of turns that each electrode has been advanced and retracted, as that is the only way to estimate where the electrode tip is located. Practice this procedure on one or two electrodes until you are sure things are working and you understand the signals you are getting. Then you can proceed to advance the remaining electrodes in the same manner. An important point to remember is that moving an electrode is likely to mechanically disrupt the signal on adjacent electrodes. This means that quite a bit of adjusting will be required to get all of the electrodes into the cortex and establish good signals on each channel. Advance only a few electrodes each day (i.e. 6-10) and randomly choose the locations of electrodes to move. This will help to distribute the compressive forces more evenly over the array. Once the electrodes are in the cortex, and you re getting signals, we recommend making very small movements from day-to-day, in the range of 1/4 to 1/2 turn. Electrodes can often be left in a fixed position for many days at a time, and this approach can be necessary if you re trying to maximize the number of simultaneously recorded signals. However, the approach you choose depends on the objective of the experiment. 29