Finite element analysis of current and potential distributions for a human auditory brainstem implant

A two-dimensional finite element model of the human head and brain stem has been developed to examine the current spread and electric fields generated during stimulation by an auditory brainstem implant. This model allows the authors to simulate different electrode positions and mono-polar or bi-polar stimulation modes. In each of the mono- or bi-polar modes, the cochlear nucleus complex (CNC) is the targeted area for stimulation. A current source of 2 mA was used in all stimulation modes, with a neighboring electrode as the ground in bipolar cases and a ground electrode on the surface of the skull on the implant side for mono-polar modes. The potentials along a tonotopic line were plotted to estimate the potential difference across the auditory brainstem structures. By analyzing iso-potential contours and current density distributions in the CNC and surrounding area, the authors found that the bi-polar mode with both stimulating plates adjacent to the CNC produced the highest potential difference inside the auditory structure. Bipolar stimulation generates greater potential differences in the vicinity of the electrodes where the CNC is located, while mono-polar modes generate fields that spread over a wider area