PMID-10498377[0] Stability of the interface between neural tissue and chronically implanted intracortical microelectrodes.
- implanted 7-shaft 35um iridium electrodes into the pericruciate gyrus of cats & measured the stability of recordings over several months.
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- electrodes were floating, under the dura; they note that connective tissue can force these floating arrays out of the brain, in further, or can encapsulate the electrodes.
- electrodes activated by 'potentiodynamic cycling' to remove the insulation from the tip, I guess.
- Insulation is epoxylite epoxy (5-10um thick) which is baked for curing and degassing at 100 and 170C each for 30 minutes.
- more information on their fabrication in {1105}
- Used the now-standard techniques for recording & analysis - amazing that this was all very new 10 years ago!
- Measure stability not only on waveform shape (which will change as the position of the electrode relative to the neuron changes) but also neural tuning.
- Lymphocytes were found to accumulate around the tips of the microstimulated sites.
- Electrode sites that yielded recordings ('active') were all clean, with large neurons near the end, and with minimal connective tissue sheath (2-8 um; distance to nearby neurons was 30-50um).
- Longest period for an active electrode was 242 days.
- Electrode impedance was usually between 50 and 75 kOhm; there was no insulation failure.
- Electrodes were stable even when the cat vigorously shook it's head in response to water placed on the head (!).
- Electrodes were very unstable the first 2 weeks - 1 month ; rather stable thereafter.
- Active electrodes tended to remain active ; inactive electrodes tended to remain inactive.
____References____
[0] Liu X, McCreery DB, Carter RR, Bullara LA, Yuen TG, Agnew WF, Stability of the interface between neural tissue and chronically implanted intracortical microelectrodes.IEEE Trans Rehabil Eng 7:3, 315-26 (1999 Sep) |
[1] Bullara LA, McCreery DB, Yuen TG, Agnew WF, A microelectrode for delivery of defined charge densities.J Neurosci Methods 9:1, 15-21 (1983 Sep) |
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