Auditory Midbrain Implant by Prof. Dr. Thomas Lenarz

The auditory midbrain implant (AMI) represents the latest frontier in Prof. Dr. Thomas Lenarz’s beyond-the-ear surgical portfolio, specifically designed for patients who cannot benefit from either a cochlear implant or a brainstem implant. While the brainstem implant (ABI) targets the first relay station of the auditory system, the midbrain implant goes one step higher to the inferior colliculus in the midbrain. This region is a major integration center for sound processing, where the brain begins to organize complex frequencies and rhythms. Under the precision of Prof. Lenarz, a specialized penetrating electrode array is inserted into the midbrain to directly stimulate neural pathways, offering a potential solution for patients with severe neuroanatomical damage or those who have not achieved successful sound perception with lower-level implants. The clinical rationale for the AMI at the Hannover Medical School is rooted in tonotopic mapping. The inferior colliculus is organized like a musical scale; specific layers respond to specific frequencies. Prof. Lenarz utilizes intraoperative multi-channel recording to ensure the electrode is positioned across these layers, aiming to replicate the natural "pitch map" of the human ear. Research conducted by Prof. Lenarz and his research partners indicates that because the midbrain is a more organized structure than the brainstem, the AMI may eventually provide superior pitch discrimination for some patients. This is particularly relevant for those with neurofibromatosis type II (NF2), where scarring from tumor removal can make the lower brainstem difficult to stimulate effectively. The surgical offer is preceded by a high-resolution DTI-MRI (diffusion tensor imaging), which acts as a digital GPS for the midbrain’s internal wiring. This scan allows Prof. Lenarz to visualize the lemniscal pathways, the high-speed data cables of the auditory system, to ensure the implant is placed in the most responsive tissue. By targeting the midbrain, the procedure aims to engage a more sophisticated level of the brain's hearing computer.