THUMBTACK MICROELECTRODE AND METHOD OF MAKING SAME

• US 3,826,244 A
• Filed: 07/20/1973
• Issued: 07/30/1974
• Est. Priority Date: 07/20/1973
• Status: Expired due to Term

• Current Assignee: Martin J. Bak, Michael Salcman
• Original Assignee: Martin J. Bak, Michael Salcman
• Inventors: Salcman, Michael, Bak, Martin J.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/381,234
• Time in Patent Office: 375 Days
• Field of Search: 128/2E,2.6B,2.6E,2.6R,2.1E,2.1R,404,418,DIG.4,2R 29/63R
• US Class Current: 600/377
• CPC Class Codes: A61B 5/283 Invasive
• CPC Class Codes: A61B 5/293 Invasive
• CPC Class Codes: A61L 31/10 Macromolecular materials
• CPC Class Codes: C08L 65/04 Polyxylenes
• CPC Class Codes: Y10T 29/49204 Contact or terminal manufacturing

Abstract

A thumbtack microelectrode for making extracellular chronic recordings from single nerve cells in the cerebral cortex in unrestrained animals over prolonged periods of time comprises a rigid electrode shaft, which is microwelded to one side of a tack head-like disc, and a flexible electrical conductor which is microwelded to the opposite side of the tack head-like disc. After a cleaning operation including ultrasonic desiccation the entire microwelded assembly is electrically insulated. The insulation covering the recording tip of the electrode shaft which is tapered, prior to the cleaning and insulating operations, by electrolytic etching, is then removed so as to expose a small area for use as the recording surface.

Claims

1. A thumbtack microelectrode for use in the chronic recording of electrical discharges from single nerve cells in the cortex of the brain of an animal comprising:

a first electrical conductor means adapted to be imbedded in a single nerve cell of the cortex of the brain of an animal for detecting electrical discharges from the single nerve cell, said first electrical conductor means having a blunt end and a tapered end;

a second electrical conductor means for anchoring and limiting the entry of said first electrical conductor means within the cortex, said second electrical conductor means having an upper and lower surface, the lower surface being substantially perpendicularly attached to the blunt end of said first electrical conductor means and adapted to be cemented to the outer surface of the cortex;

a third electrical conductor means fixedly attached to the upper surface of said second electrical conductor means for transmitting the detected electrical discharges from the cortex to the exterior of the skull of the animal; and

insulation means totally encompassing the outer surface of said second and third electrical conductor means and all of said first electrical conductor means except the tapered end thereof for insulating the covered areas when the microelectrode is inserted in the cortex.

2. The device of claim 1 wherein said first electrical conductor means is a rigid elongated iridium shaft.

3. The device of claim 1 wherein said second electrical conductor means is a rigid platinum disc.

4. The device of claim 1 wherein said third electrical conductor means is a flexible platinum-iridium wire.

5. The device of claim 1 wherein said insulation means includes:

a Teflon covering for said third electrical conductor means; and

a parylene covering for said first and second electrical conductor means.

6. The device of claim 1 wherein the non-insulated tapered end of said first electrical conductor means is from 10 to 20 micrometers in length and from 1 to 3 micrometers in diameter.

7. A thumbtack microelectrode for use in the chronic recording of electrical discharges from single nerve cells in the cortex of the brain of an animal comprising:

a rigid, elongated, electrically conducting electrode shaft having a blunt end and a tapered end, the tapered end being the only portion of said electrode shaft not electrically insulated;

a rigid electrically insulated, electrical conducting disc having an upper and lower surface, the lower surface being substantially perpendicularly attached to the blunt end of said electrode shaft; and

a flexible, electrically insulated, elongated wire fixedly attached to the upper surface of said disc for transmitting the detected electrical discharge from the cortex to the exterior of the skull of the animal.

8. A method of making a thumbtack microelectrode comprising the steps of:

providing a disc of an upper and lower surface;

microwelding to the upper surface of said disc an elongated, flexible, insulated electrical conductor;

microwelding to the lower surface of said disc one end of an elongated, rigid, bare electrical conductor;

bending said bare electrical conductor at substantially a right angle to the lower surface of said disc;

electrolytically etching the free end of said bare electrical conductor until the desired tip configuration is achieved;

cleaning the microwelded assembly;

vacuum depositing a layer of insulating material of low biological toxicity over said disc and said bare electrical conductor; and

removing a small amount of the insulating material from the electrolytically etched tip of said bare electrical conductor.

9. The method of claim 8 wherein the bare electrical conductor is electrolytically etched in a bath of supersaturated sodium cyanide- 30 percent sodium hydroxide.

10. The method of claim 8 wherein the cleaning step includes:

rinsing the microwelded assembly in hydrochloric acid, then in distilled water;

placing the microwelded assembly in an acetone bath;

ultrasonicly desiccating the microwelded assembly for 15 seconds in distilled water, then for another 15 seconds in methanol; and

oven drying the microwelded assembly at 60*C.

11. The method of claim 8 wherein the vacuum deposition step includes:

vaporizing 2 gm of parylene dimer at 260*C;

pyrolysizing the parylene at 700*C; and

subsequent polymerization of the parylene.

12. The method of claim 8 wherein the insulation removal is achieved by burning away the insulation.

13. The method of claim 8 wherein the insulation removal is achieved by melting the insulation with the beam of a ruby laser.

14. The method of claim 8 wherein the insulation removal is achieved by abrading off the insulation.