user’s manual for the tangential recording chamber and ......the microdrive is mounted within the...

User’s manual for the tangential recording chamber and SC32 microdrive system

1. Description of the chamber system ----------------------------------------- 2-4

2. Description of the microdrive system -------------------------------------- 5-7

3. Chamber implantation -------------------------------------------------------- 8-21

4. Microdrive implantation ----------------------------------------------------- 22-27

5. Advancing electrodes and recording neural activity --------------------- 28-30

Gray Matter Research, LLC – www.graymatter-research.com 1

Tangential Chamber System

The tangential chamber (Fig.1) provides

hermetically sealed access to the brain. It

is designed to be mounted tangential to the

cortical surface within a 5/8” diameter

craniotomy. Its lower wall should fit

snuggly into the craniotomy, with the

bottom surface of the wall resting gently,

and in uniform contact with the surface of

the dura. The chamber is attached to the

skull with bone screws and acrylic bone

cement. It contains an internal sleeve with

a Silastic membrane mounted on the

bottom surface. A silicone o-ring rests in a

groove on the top of the chamber wall.

When the sleeve is tightened it compresses

the o-ring and provides a water-tight seal.

A plug is mounted within the sleeve to

prevent herniation and the chamber is

covered with a protective cap. Figure 1. Exploded view of the

tangential recording chamber system.


Parts List RC-T-S-Ti

Figure 2. Tangential chamber components list.

Item# Description Quantity/System

1. Chamber 1

2. Chamber Sleeve 2

3. Silastic Ring 2

4. Chamber Plug 2

5. Chamber Cap 2

6. Removal Tool 1

7. O-ring 5


Silastic Membrane Assembly

Gray Matter Research, LLC – www.graymatter-research.com

Figure 3. Photographs illustrating the sequence of steps for mounting the Silastic membrane

onto the chamber sleeve.

4

A. Top: Chamber sleeve oriented upside down. Bottom: Silastic ring.

B. A small piece of Silastic membrane is placed over the bottom surface of the chamber sleeve (shiny side up).

C. The Silastic ring is placed on top of the membrane and aligned to the chamber sleeve.

D. View of the membrane/sleeve following the mounting of the ring. In this step uniform downward pressure is applied to

the ring until is it seated firmly onto the sleeve. When done correctly there should be no holes or tears in the Silastic

membrane. This must be confirmed by inspecting the integrity of the membrane using a operating/dissecting microscope.

E. Completed assembly after the residual membrane has been removed using a #11 scalpel at the interface between the

sleeve and the ring. It is important to fully remove all membrane at the interface otherwise this may impede the fit between

the sleeve and the chamber.

Tangential Microdrive System (SC32-16mm)

Figure 4. Exploded view of the SC32. Actuators,

including the lead screw, compression spring, shuttle

and electrode, are not shown.

The tangential microdrive system (Fig.3) is

designed to be semi-chronically implanted within

the tangential chamber and provide independent

control of 32 microelectrodes (SC32). 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. The microdrive is

held firmly within the chamber using a retaining

cap. A silicone o-ring, provides a water-tight

seal. Bone cement is applied to the outside of the

retaining cap to reinforce the implant and provide

impact resistance.


Figure 5. Parts List SC32


Item# Description Quantity

1. Retaining Cap 1

2. Protective Cap 1

2a. Fastening screws 6

3. Lead Screw Driver 3

4. Ground wire 2

5. Actuator Block 1

6. Screw Guide 1

7. Printed Circuit Board 1

8. Lead Screw 32

9. Tear Drop Shuttle 32

10. Compression Spring 32

11. Silicone O-ring 1

12. Female Grounding Pin 4

13. Male Grounding Pin 4

14. 1.2 x 0.25" unm screw 2

15. 1.2 x 0.375" unm screw 4

16. Hex Driver (ns) 1

17. Screwdriver (ns) 1

18. Holder (ns) 1

19. Swivel Clamp (ns) 1

Assembled Chamber and Microdrive Systems

Figure 6. Multiple views of an assembled tangential chamber and microdrive system (SC32).


Implantation of the Tangential Chamber and SC32 Microdrive

Figure 7. MRI-based skull model with stereotaxic coordinates marked by a point and the chamber

outline marked with a circle.


Figure 8. Once the appropriate chamber location is identified, a 5/8” diameter craniotomy can be

made.



9

Figure 9. If needed, the bone surface around the external perimeter of the craniotomy can be

beveled to improve the fit of the chamber. The inset shows a cutaway view of the beveled surface

highlighted in blue.



10



11

Figure 10. Once the craniotomy is made, holes can be drilled for anchoring bone screws (#44

drill, .086” diameter). It’s very important to use a sufficient number of bone screws to provide

resistance to impacts. Holes for 12 screw are shown here.

Figure 11. Bone screws are then screwed into each hole. (Inset: GMR bone screw) It’s very

important to use a sufficient number of bone screws to provide resistance to impacts. 12 screws

are shown here.



12

Figure 12. Photograph of a surgical craniotomy over visual cortex illustrating the relationship

between the craniotomy, exposed dural membrane, the beveled cranial bone and the bone screws.



13

Figure 13. The chamber is mounted within the craniotomy. The bottom surface of the lower

chamber wall should rest gently and uniformly on the surface of the dural membrane.



14

Figure 14. Coronal cutaway view through the middle of the chamber illustrating the relationship

between the chamber, the craniotomy and the dural membrane (blue).



15

Figure 15. A thin bead of Metabond bone cement (yellow) should be applied, using a 1 or 3 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. It is

important that the Metabond is sufficiently viscous to avoid it flowing underneath the chamber

and onto the dura.

C&B Metabond http://www.parkell.com/ Essential items: S371 (Catalyst), S398 (Quick Base), S399 (L-Powder), S387 (Mixing dish)

Mixing ratio: 6 scoops of powder, 24 drops of base, 6 drops catalyst



16

http://www.parkell.com/

Figure 16. 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.



17

Figure 17. Coronal cutaway view illustrating the relationship between the chamber and the bone

cement (pink). The cement should flow into the groove of the chamber and cover all of the

screws. The outer border of the bone cement should be as smooth and continuous as possible. Be

careful not to apply cement above the upper chamber flange as this can interfere with the mating

chamber cap and retaining cap.



18

Figure 18. Exploded view illustrating the placement of the o-ring, the chamber sleeve, the plug

and the cap. Before placing the sleeve, the chamber cavity should be thoroughly rinsed with a 4:1

solution of sterile saline and Betadine, followed by sterile saline, and then suctioned dry.



19

Figure 19. The chamber cap is installed as the final step. At this stage the chamber interior should

not require cleaning. Whenever the cap, plug, sleeve and o-ring are removed they should be

replaced with identical sterile parts.



20

Figure 20. Cutaway view of the installed chamber system.



21

Figure 21. Exploded view of the assembled microdrive (SC32) positioned above the chamber.

The microdrive contains a centering pin on the underside of the flange (arrow). This must be

properly aligned with one of the holes on the top surface of the chamber sleeve.



22

Figure 22. The microdrive 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.



23

Figure 23. Coronal cutaway view of the microdrive installed within the chamber. The arrow

points to the junction between the upper chamber flange and the bottom of the retaining cap. A

small (.010 inch) gap should be visible once the retaining cap is seated correctly.



24

Figure 24. An additional (2nd) 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. Avoid applying

highly liquid cement at the junction between the retaining cap and the chamber.



25

Figure 25. Coronal cutaway view of the microdrive installed within the chamber after the

reinforcing (2nd) layer of bone cement is applied to the retaining cap. Care should be taken to

prevent the liquid acrylic from flowing into the junction between the retaining cap and chamber

(arrow).



26

Figure 26. Fully assembled system with protective cap. Avoid over tightening the fixation screws

on the protective cap and never use set screws. Set screws can easily strip.



27


Figure 27. 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 (pink).

Silicone sealant (~0.5 mm thick) is applied to the bottom surface of the microdrive (green). The

Silastic membrane is shown in red, the dural membrane in cyan, and the 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, the

membrane and the dura.

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 ~0.5-1.0 mm thick.

To make electrical contact with the animal it is necessary to advance the electrode by ~2.0-2.5 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 and

membrane). 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.



The dura is likely to dimple by a variable amount (~0.5-2.0 mm) as the electrode passes through the tough

membrane. This can lead to a recoil of the dura (and cortex) 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.


user’s manual for the tangential recording chamber and ......the microdrive is mounted within the...

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