Cortical Inhibition Predicts Recovery of Function from Auditory Nerve Damage (in Mice)

Hey neuroscience fans, I thought you might hearing about this recently published study - http://dx.doi.org/10.7554/eLife.21452. Disclaimer: this is not a research study that tested a new treatment for tinnitus (nor does it purport to do anything of the sort). But it does shed some light on the central importance of rapid swings in cortical inhibition as a key determinant in whether the brain can effectively reorganize after auditory nerve damage or not.

The authors used some fancy technology only available in transgenic mice to track the firing patterns of single neurons in the auditory cortex for several months before and after either moderate or massive auditory nerve damage. They used an optogenetic strategy to monitor daily changes in the level of inhibition as cortical neurons struggled to recover sound processing after damage.

What does this have to do with tinnitus? 1) this study looks at all the physiological markers that are usually thought to underlie tinnitus (increased spontaneous firing rate, increased central gain, tonotopic map plasticity) but really underscores the importance of inhibition as the key biomarker for how well brains can recovery from peripheral nerve injury, 2) all mice received the identical injury but some mice recovered nearly normal thresholds while others never recovered auditory sensitivity. It's the same with T; after intense noise exposure, one person's brain will drive itself off a cliff and generate pathological patterns of activity that generate phantom sounds and the other person will recover normally. This paper suggests that the key predictor of how brains reorganize after injury can be traced to how networks of inhibitory cells react in the first few days after the injury. This is also key idea in stroke treatment; if you change levels of cortical inhibition after ischemia you can change the ultimate path of recovery months later. Maybe the same is true for tinnitus.