J. S. Pezaris, M. Sahani, K. L. Grieve, and R. A. Andersen, Multiple Single Unit Recording Using Tetrodes in Macaque Visual Cortex: Electrode Design and Spike Identification, Poster 360.4, Society for Neuroscience 25th Annual Meeting, San Diego, November 1995.



MULTIPLE SINGLE UNIT RECORDING USING TETRODES IN MACAQUE VISUAL CORTEX: ELECTRODE DESIGN AND SPIKE IDENTIFICATION

J. S. Pezaris, M. Sahani, K. L. Grieve, R. A. Andersen

Division of Biology
Computation and Neural Systems
Caltech, Pasadena, CA 91125


Abstract

We have adapted the McNaughton-Wilson tetrode for use in the awake behaving monkey preparation. Our design combines a standard guide tube for puncturing dura with a much finer carrier tube to hold the tetrode bundle. The assembly is manipulated using standard hydraulic microdrives, assuring good positional accuracy.

Eleven penetrations were made into parietal cortex. Tetrodes were made with 15 and 25 um insulated commercial nichrome wire running in oil-filled 33 gauge stainless steel carrier tubes. Two control penetrations were made with standard tungsten wire electrodes. Direct digital recordings were made of the four-channel waveforms.

Histology shows that the tetrode wire runs straight up to our maximum extension of 12 mm, and that the carrier tube does not cause excessive neural trauma. Tracks left by the three electrode types are nearly identical.

Coarse analysis of recorded data shows the tetrode wires compare favorably against traditional coated tungsten electrodes in terms of impedance (0.5-0.7 MOhm vs. 0.8 MOhm), signal pickup, and signal to noise ratio (15:1 vs. 23:1).

Finer analysis of recorded data shows clearly separable multi-unit activity. Initial analysis was done by clustering four-channel peak height. We observed that false clusters were created by simultaneous firing of distinct units. Additional analysis was done using M. S. Lewicki's Bayesian waveform classification tools. This resulted in classification consistent with the peak height analysis, while resolving simultaneous activity.

For additional information, we refer the reader to
our CNS*95 presentation,
which contains substantially the same material.
We plan to eventually unify the two presentations,
the result of which will be made available here.

John Pezaris
Caltech
Mail Code 216-76
Pasadena, CA 91125
john@pezaris.com
17 October 1995