Auditory Brainstem Implants
Our primary research seeks to better understand the restoration of auditory sensation through the stimulation of the Cochlear Nucleus in the brainstem. In clinical practice, this is currently accomplished through a Auditory Brainstem Implant (ABI), which is an electrode paddle surgically implanted to interface with the cochlear nucleus. Patients require an ABI when they do not possess a functional cochlea (Cochlear malformations/ossification) or cochlear nerve
(trauma during tumor excision in Neurofibromatosis Type 2 patients) and thereby do not benefit from Cochlear Implantation or conventional amplification methods. We currently work with mice and cadaveric models.
Optical Stimulation of the Auditory System
Our recent work in the ABI lab has included the first efforts to optically stimulate neurons in the central auditory system using optogenetics. In contrast to electricity, light offers a theoretical advantage as it can be focused and may allow for the selective activation of hundreds of independent acoustic channels. We use novel Adenovirus Associated Vectors (AAVs) packaged with opsins to transfect mice cells with the opsins in vivo, then optically stimulate the cochlear nucleus via laser to observe auditiory responses.
Magnetic Stimulation of the Auditory Pathway
The cochlear implant (CI) provides auditory perception to patients with hearing loss by electrically stimulating spiral ganglion neurons along their tonotopic axis within the cochlea. However, outcomes have plateaued with contemporary designs. Most patients with the CI experience poor pitch resolution characterized by limited speech perception in background noise and poor music appreciation. This occurs because electric stimulation within the highly conductive intracochlear fluid results in current spread and indiscriminate activation of broad neuronal populations by neighboring electrodes. In collaboration with the Fried Laboratory at MGH, we recently evaluated a novel intracochlear stimulation modality—micro-coil magnetic stimulation—and quantified the spread of auditory pathway activation by recording multi-unit responses from the inferior colliculus (IC) in deafened mice. Compared to electric intracochlear stimulation, magnetic stimulation had narrower spectral spread of activation and increased dynamic range. With the support of a recently awarded American Hearing Research Foundation Discovery Grant (www.american-hearing.org), we are further evaluating the feasibility of a next generation magnetic micro-coil based cochlear implant in a guinea pig model. We are also interested in investigating whether magnetic stimulation of the cochlear nucleus can enable more effective auditory brainstem implant designs.
3D Brain Reconstruction Using Imaging
By the nature of the human brain anatomy, visualizing the cochlear nucleus during ABI surgery is virtually impossible, thus making the actual placement of the ABI a “blind” prodedure assisted only by surgical landmarks. This results in varied degrees of actual electrode contact with the cochlear nucleus, and in turn varied auditory performance. Using real patient CT and MRI imaging, we are able to create 3D reconstructions of patients with ABI and observe implant positioning associated with respective outcomes.