Evaluation of the current distribution of the hybrid common ground stimulation in cochlear implants

International audience; BackgroundIn cochlear implants, the hybrid common ground is a combination of a classic monopolarstimulation with a standard common ground. This new stimulation montage allows the current toreturn from both the non-stimulating electrodes on the electrode array and the reference electrodeplaced between the skull and scalp. In theory, this lead to reach a compromise between the currentfocality and the efficiency of the stimulation. Even if this stimulation type has already been adoptedby some implant manufacturers, the 3D geometry of its current pathways remains to be studied.MethodsThe study is two-fold. First, an in-vitro experiment aimed to measure the electrical field producedby the hybrid common ground stimulation. An electrode array of an XP implant (Oticon Medical,Neurelec) was placed in saline solution and the electrical field was recorded by a probe that movesalong the programmed grid. During the stimulation, the current waveforms on all the groundingelectrodes were also recorded. Second, an in-situ measurement was conducted. Another XP devicewas implanted into a human specimen. The same procedure as in the in-vitro measurement wasperformed to record, this time, the current waveforms only.ResultsThe recorded two groups of current data were compared with each other to investigate how thecurrent path is modified by the geometry of a human cochlea. The potential distribution measuredduring the in-vitro experiment was also compared with other stimulation types such as monopolar.The energy consumption of the stimulation was also computed from the collected data.