In vivo comparison of the charge densities required to evoke motor responses using novel annular penetrating microelectrodes

Emma K. Brunton, Bjorn Winther-Jensen, Chun Wang, Edwin B. Yan, Saman Hagh Gooie, Arthur J. Lowery, Ramesh Rajan

Research output: Contribution to journalArticleOtherpeer-review

14 Citations (Scopus)


Electrodes for cortical stimulation need to deliver current to neural tissue effectively and safely. We have developed electrodes with a novel annular geometry for use in cortical visual prostheses. Here, we explore a critical question on the ideal annulus height to ensure electrical stimulation will be safe and effective. We implanted single electrodes into the motor cortex of anesthetized rats and measured the current required to evoke a motor response to stimulation, and the charge injection capacity (CIC) of the electrodes. We compared platinum iridium (PtIr) electrodes with different annulus heights, with and without a coating of porous titanium nitride (TiN). Threshold charge densities to evoke a motor response ranged from 12 to 36 μ Electrodes with larger geometric surface areas (GSAs) required higher currents to evoke responses, but lower charge densities. The addition of a porous TiN coating did not significantly influence the current required to evoke a motor response. The CIC of both electrode types was significantly reduced in vivo compared with in vitro measurements. The measured CIC was 72 and 18 μ for electrodes with and without a TiN coating, respectively. These results support the use of PtIr annular electrodes with annulus heights greater than 100 μm (GSA of 38, 000 μm2). However, if the electrodes are coated with porous TiN the annulus height can be reduced to 40 μm (GSA of 16,000 μm2).
Original languageEnglish
Number of pages11
JournalFrontiers in Neuroengineering
Issue number5
Publication statusPublished - 2015


  • Neural prosthesis
  • Microelectrodes
  • Charge injection capacity
  • in vivo
  • Neural stimulation

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