The mechanism of cochlear implant restoration of hearing is elucidated

This image shows X-rays taken from two different angles showing human and rat cochlear implants. Human cochlear electrodes have 22 channels, rats have 8, and in both cases the electrodes are rotated 360 degrees in the cochlea to provide electrical stimulation and restore hearing. Image source: "Nature" website

The British magazine Nature published a rat study on the 22nd, which for the first time clarified the neural mechanism that allows cochlear implants to restore hearing. This research could help improve the performance of these widely used medical devices.

Cochlear implants can help restore hearing to completely deaf patients, but patient responses vary widely. Some implant patients can understand conversations within hours of activation of the implant, but some experience little improvement even months later.

To understand the reason, a research team from New York University School of Medicine in the United States customized cochlear implants for 16 deaf rats to study their brain activity patterns related to hearing recovery. Like humans, rats' responses to the implants varied widely: In this study, activation of the locus coeruleus, a brainstem region associated with learning, predicted positive responses. When this brain area was artificially activated, the observed differences between animals disappeared—all rats stimulated in this way showed responses to sounds within days of implantation.

Neurons in the locus coeruleus produce and release the neuromodulatory substance norepinephrine, which in turn affects the structure and function of multiple neural networks. This brain "rewiring" is a key feature of learning; when cochlear implants are unsuccessful, it may be because the locus coeruleus is not fully engaged and the brain fails to rewire neural networks.

The researchers believe that therapeutic strategies that engage this targeted brain region could lead to the optimization of neural implant devices.