Cochlear Synaptopathy
- Neil Freebern
- Jun 2
- 5 min read
Updated: Jun 3
In my quest to understand my hearing disability, I have discovered that there are three issues at play.
Hearing loss - volume loss of 60dB at and around 6 KHz
Tinittus - A response to the volume loss, added noise is generated in the head.
Cochlear Synaptopathy - a distortion of sound when volume levels exceed the level of quiet speach.
The distortion of sound, not the tinnitus, is preventing me from making music or even listen to it at a decent volume. Disvcovering cochelear synaptopathy, gives me at least some answers to where the distortion is coming from, and opens up options for treatment.
What is Cochlear Synaptopathy? The Hidden Hearing Loss No One Told You About
You’ve had your hearing tested. The audiogram says you’re “within normal limits.” But something’s off. Conversations in noisy places feel like chaos. Certain sounds distort, or feel harsh and brittle. And there's a buzz—or maybe a hiss—haunting the quiet moments. You walk away thinking, It’s not just in my head, right?
If this sounds familiar, you might be dealing with cochlear synaptopathy—a lesser-known but very real condition also called hidden hearing loss.
What Is Cochlear Synaptopathy?
Cochlear synaptopathy is damage not to your hair cells (which traditional hearing tests measure), but to the synapses—the microscopic connections between those hair cells and the auditory nerve. When those connections are frayed or broken, sound signals become fuzzy, incomplete, or distorted by the time they reach your brain.
The result? You may “hear” sounds, but you don’t understand them—especially in challenging environments. It’s like having a perfectly good speaker with a frayed cable. The system works, but the signal gets scrambled.
What Causes It?
Cochlear synaptopathy can be triggered by:
Noise exposure (concerts, machinery, earbuds cranked too loud)
Aging
Ototoxic medications
Sometimes, the cause isn’t clear.
Often, it’s the damage you don’t notice in the moment—a loud event that doesn’t leave you deaf, but quietly changes how you hear forever.
How Do You Know You Have It?
Here’s what many people with cochlear synaptopathy report:
Difficulty understanding speech in noisy environments
Tinnitus (ringing or buzzing in the ears)
Sound distortion, especially at higher volumes or frequencies
A disconnect between how well you “should” hear and how you actually hear
Standard hearing tests usually miss it. Diagnosis often requires advanced tools like auditory brainstem response (ABR) testing or speech-in-noise assessments.
Is There a Treatment?
Right now, treatment is limited—but evolving. Researchers are developing therapies aimed at repairing those damaged synapses. One of the most promising is a drug called CIL001, currently in clinical trials, which aims to restore those lost connections.
There are several promising approaches to treating cochlear synaptopathy, though many are still in the research phase. Here are some potential treatments:
Neurotrophic Factors: Certain drugs, like NT-3 (neurotrophin-3), have shown promise in regenerating cochlear synapses in animal studies. These compounds promote nerve fiber growth and could help restore auditory function.
Pharmacological Interventions: Some experimental drugs aim to protect or restore synaptic connections in the cochlea. Cilcare, a biotech company, is developing CIL001, a treatment targeting cochlear synaptopathy, with clinical trials planned for 2025.
Gene Therapy: Researchers are exploring gene therapy techniques to repair damaged synapses and improve hearing function. While still in early stages, this approach could offer long-term solutions for synaptopathy.
Electrophysiological Stimulation: Some studies suggest that electrical stimulation of the auditory nerve may help restore synaptic function, though this method requires further investigation.
Hearing Aids and Cochlear Implants: While these devices do not directly treat synaptopathy, they can help compensate for hearing difficulties by amplifying sound and improving speech perception.
The field of cochlear synaptopathy treatment is evolving, and researchers are working toward developing effective therapies
Why It Matters
Cochlear synaptopathy changes how you experience the world—but too often, it goes unrecognized. If you feel like your hearing isn’t “right” even though the tests say otherwise, trust yourself. If you have hearing loss and tinittus, you may also have additional distortion which could be at the synaptic level. What sounds are created in your head and how do they differ? In my case, I have loss of volume, added tinittus pitch and distortion when volumes get loud.
The distortion, I believe is synaptopathy.
Auditory Brainstem Response (ABR) testing
This test may give some evidence that syaptopathy is in play.
ABR testing checks the electrical activity in your auditory pathway—from your inner ear up through the brainstem—in response to clicking sounds or tone bursts. It's like an EEG for your hearing system.
How Does It Work?
Electrodes are placed on your scalp and earlobes (or behind the ears).
You wear earphones that deliver specific sounds—like clicks or tone bursts.
The test records your brain’s automatic electrical responses to those sounds, in the form of waveforms.
Each "wave" corresponds to a specific part of your auditory pathway. Audiologists analyze the timing and shape of these waves to see if there’s a delay, disruption, or drop in neural firing.
Why Is It Useful?
Cochlear Synaptopathy: ABR may show a reduced wave I (which reflects auditory nerve activity), even if the rest of your hearing looks normal.
Tumors or nerve damage: Can reveal if something’s compressing or affecting the auditory nerve.
Unexplained hearing loss: Helps determine whether the problem is in the ear or in the brainstem.
⏱️ What to Expect
The test takes about 30–60 minutes.
You’ll be lying down, relaxed, and possibly even allowed to nap.
No response is required from you—it’s passive and completely painless.
Effects on Auditory Nerve Fibers: Early research suggested that cochlear synaptopathy mainly damages low-spontaneous rate auditory nerve fibers, which help distinguish sounds in noisy environments. However, more recent studies indicate that it may affect all types of auditory nerve fibers. Surprisingly, some cases have shown enhanced neural activity—possibly because the remaining fibers adapt and become more efficient at processing sound
Implications for Clinical Research: The evolving understanding of synaptopathy suggests that researchers must refine testing methods to better detect and characterize it in humans. This could eventually lead to treatments that help restore synaptic connections and improve hearing.
Enhanced neural activity in cochlear synaptopathy appears to occur in the central auditory system, rather than at the site of synaptic damage in the cochlea. Research suggests that when synapses in the cochlea are lost, the brain compensates by increasing neural gain—essentially amplifying signals in the auditory pathway. This phenomenon, known as central gain enhancement, has been observed in tinnitus patients with normal hearing thresholds, indicating that the brain may be trying to make up for lost auditory input