TITLE: Electrophysiological recording from a chronic chamber-implanted non-human primate
AUTHORS: Witold J Lipski, Daisuke Kase, Devin R Harsch, Robert S Turner

[DESCRIPTION]
This protocol describes the preparation and insertion of extracellular recording electrodes into intracranial targets of a non-human primate implanted with a chronic recording chamber. A piercing guide cannula is used to penetrate the dura and to guide the electrode. Practices related to targeting, electrode cleaning, and electrode movement and settling relative to brain tissue are discussed.

[STEPS]
SECTION: Preparation before the day of recording
1. Choose the target area using resources such as an MRI or prior brain mapping.
SECTION: Preparation before the day of recording
2. Calculate the distance from the micro-drive to the surface of the brain.

 

SECTION: Preparation before the day of recording
3. Draw a mark on the dura piercing guide at the calculated distance from the tip.

 

SECTION: Preparation before the day of recording
4. Mount an electrode or multi-electrode-array on the micro-drive.
SECTION: Preparation before the day of recording
5. Cover the micro-drive and leave a message for other lab members to exercise caution when working near the micro-drive to avoid accidental damage.
SECTION: Preparation before chairing the animal
6. Check that the recording system is working properly.
SECTION: Preparation before chairing the animal
7. Clean the electrode and piercing guide (follow the instructions for the specific electrode in use). For our recordings, we soak the electrode and piercing guide in a 1% solution of enzymatic detergent (Metrex, EmPower Dual-Enzymatic Detergent) for 30 minutes, followed by multiple rinses with sterile water, and then another rinse with saline.
SECTION: Preparation after chairing the animal
8. After chairing the animal, secure the animal with restraints such as arm restraints and a neck-plate.
SECTION: Preparation after chairing the animal
9. Secure the animal's head using head-fixation posts.
SECTION: Preparation after chairing the animal
10. Wipe the surface of the implant with a sani-cloth (PDI health care).
SECTION: Preparation after chairing the animal
11. Clean the recording chamber (see our other protocol).
SECTION: Preparation after chairing the animal
12. Fill the chamber with saline so that any tissue is not exposed to air.
SECTION: Preparation after chairing the animal
13. Transfer the animal into the recording rig.
SECTION: Piercing the dura and lowering the electrode
14. Rinse the electrode and piercing guide with sterile water and saline.
SECTION: Piercing the dura and lowering the electrode
15. Mount the micro-drive on the animal’s head.
SECTION: Piercing the dura and lowering the electrode
16. Connect the micro-drive to the depth monitor if available.
SECTION: Piercing the dura and lowering the electrode
17. Check/note the offset of the electrode if the depth on the monitor is not zero.
SECTION: Piercing the dura and lowering the electrode
18. Connect the electrode to the recording system.
SECTION: Piercing the dura and lowering the electrode
19. Lower the piercing guide to the marked depth (surface of the dura).

 

SECTION: Piercing the dura and lowering the electrode
20. Lower the electrode 1-2 mm above the dura with coarse drive.
SECTION: Piercing the dura and lowering the electrode
21. Start monitoring the signal from electrode.

 

SECTION: Piercing the dura and lowering the electrode
22. Start lowering the electrode with the fine drive until researchers can confirm the spike activity. 

 

SECTION: Piercing the dura and lowering the electrode
23. Continue lowering the electrode to the target depth. 

 

SECTION: Piercing the dura and lowering the electrode
24. Lower the electrode 0.5 to 1 mm below the target depth.
SECTION: Piercing the dura and lowering the electrode
25. Wait for 10 minutes (it is recommended to let the animal do a behavioral task or to give reward to the animal during this period. Movement of the face and jaw aids in settling the electrode).
SECTION: Piercing the dura and lowering the electrode
26. Pull up the electrode to the target depth.
SECTION: Piercing the dura and lowering the electrode
27. Wait for 50 minutes. This is especially important when recording from deep structures to account for any potential movement of the brain that occurred while lowering the electrode.

 

SECTION: Piercing the dura and lowering the electrode
28. Start the recording.

 

SECTION: After the recording
29. Pull up the electrode slowly all the way.
SECTION: After the recording
30. Pull up the piercing guide.
SECTION: After the recording
31. Unmount the micro-drive.
SECTION: After the recording
32. Move the animal from the recording chamber to the place for chamber cleaning.
SECTION: After the recording
33. Clean the chamber as outlined in our other protocol.
SECTION: After the recording
34. Put the chamber cap back on the chamber.
SECTION: After the recording
35. Return the animal to its home cage.
SECTION: After the recording
36. Clean the electrode and piercing guide (follow the instructions for the electrode being used).