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.
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.