Focused intracochlear electric stimulation with phased array channels

Abstract

A method is described for producing focused intracochlear electric stimulation using an array of N electrodes. For each electrode site, N weights are computed that define the ratios of positive and negative electrode currents required to produce cancellation of the voltage within scala tympani at all of the N-1 other sites. Multiple sites can be stimulated simultaneously by superposition of their respective current vectors. The method allows N independent stimulus waveforms to be delivered to each of the N electrode sites without spatial overlap. Channel interaction from current spread associated with monopolar stimulation is substantially eliminated. The method operates by inverting the spread functions of individual monopoles as measured with the other electrodes. The method was implemented and validated with data from three human subjects implanted with 22-electrode perimodiolar arrays. Results indicate that (1) focusing is realizable with realistic precision; (2) focusing comes at the cost of increased total stimulation current; (3) uncanceled voltages that arise beyond the ends of the array are weak except when stimulating the two end channels; and (4) close perimodiolar positioning of the electrodes may be important for minimizing stimulation current and sensitivity to measurement errors.

Temporal Considerations for Stimulating Spiral Ganglion Neurons with Cochlear Implants

“…Therefore, efforts to reduce current spread have been proposed that could lead to the reduction of subthreshold effects and the targeting of smaller subpopulations of SGNs per channel. Some promising methods are being developed for more accurately steering current towards the intended SGNs, such as using bipolar, tripolar, or even multipolar electrode configurations (van den Honert and Kelsall 2007).…”

Perceptual Interactions Between Electrodes Using Focused and Monopolar Cochlear Stimulation

“…They agreed to use the research device for 18 months and to participate in research during this time. While not participating in experiments, the participants connected their research implant to a standard sound processor programmed with the ACE strategy (Vandali et al 2000) using a custom-designed dongle (van den Honert and Kelsall 2007). After the research period, participants were explanted and reimplanted with a standard commercial cochlear implant.…”

“…Van den Honert and Kelsall (2007) have demonstrated that if the impedance matrix between all pairs of electrodes can be measured, it is possible to create a potential field localized around one targeted electrode. By selecting simultaneous current levels and phases on each electrode appropriately, the sum of all potentials can result in a gradient confined to a very specific place in the cochlea (schematically shown in Fig.…”

“…The third experiment compared the temporal interactions across electrode positions in both modes. Based on behavioral and physiological data and computational models (van den Honert and Kelsall 2007;Bonham and Litvak 2008;Frijns et al 2011), the AP mode was expected to show (1) less current summation, (2) a narrower masking pattern, and (3) less temporal interaction than the MP mode.…”

“…Therefore, the experiment was undertaken using an experimental stimulator provided by Cochlear Ltd that was equipped with 22 independent current sources. This stimulator was connected to an implanted intra-cochlear electrode array via a percutaneous connector (van den Honert and Kelsall 2007). A series of experiments was performed to test the spatial specificity of AP stimulation compared to MP stimulation.…”