Tinnitus and Hyperacusis: Neural Signatures Revealed

A new study from Harvard Medical School researchers provides some of the clearest evidence yet that tinnitus and hyperacusis, often experienced by people with normal hearing, are rooted in hidden nerve damage and distinct brain responses. The work, led by Viacheslav Vasilkov and M. Charles Liberman at Massachusetts Eye & Ear, identifies separate neural “signatures” for these common yet poorly understood conditions.

Detecting Hidden Damage in a “Normal-Hearing” Ear

The research team recruited adults with clinically normal hearing thresholds. All participants had standard audiometric results (≤20 dB HL from 0.25 to 8 kHz) and normal extended high-frequency hearing. They then used a technique called click-evoked electrocochleography (ECochG) to look deeper than the audiogram.

ECochG records the ear’s electrical responses to sound. The team applied a novel filtering approach to separate the signal into its component parts. High-frequency filtering (470 to 3000 Hz) isolated the rapid responses from the auditory nerve itself. Low-frequency filtering (3.3 to 470 Hz) captured the slower, summed responses from populations of neurons in the auditory brainstem. This method allowed the scientists to disentangle peripheral damage from central brain changes. Participants also completed the Hyperacusis Handicap Questionnaire (HHQ) and reported their tinnitus status.

Two Symptoms, One Peripheral Problem

The high-frequency, peripheral ECochG data revealed a consistent finding: both tinnitus and higher HHQ scores (indicating sound sensitivity) were independently associated with reduced response amplitudes from the auditory nerve. This is a direct electrophysiological sign of cochlear nerve degeneration (CND)—a loss of neural fibers that is completely invisible on a standard hearing test.

“This confirms a growing theory that the audiogram is an incomplete picture of hearing health,” said senior author Stéphane Maison. “Many people with normal thresholds are living with a significant loss of neural input to the brain.” This shared peripheral deficit helps explain why tinnitus and hyperacusis frequently co-occur.

Divergent Brainstem Signatures: Gain in Different Places

Where the results became particularly revealing was in the brainstem responses. The analysis showed that the two conditions are not the same in the brain.

In participants with tinnitus, the researchers found selectively elevated gain at the level of the cochlear nucleus. This is the very first synaptic relay station in the brain for sound information. The amplification was present in the high-pass filtered waveforms, regardless of the person’s HHQ score.

For participants with high hyperacusis questionnaire scores, a different pattern emerged. The low-pass filtered responses showed that a later brainstem component, and the ratio of this later response to an earlier one, was specifically increased. This effect was independent of whether the person had tinnitus.

“We saw two different fingerprints,” explained Vasilkov. “Tinnitus correlated with a boosted signal very early in the pathway. Hyperacusis was linked to altered processing at a subsequent stage. This suggests the brain compensates for the same weak nerve signal in different ways, potentially leading to different symptoms.” Statistical models confirmed that the effects of nerve loss on tinnitus and on sound sensitivity only partially overlapped; one symptom did not fully explain the other.

Implications for Diagnosis and Future Treatment

These findings have direct practical implications. They offer a physiological explanation for the clinical observation that tinnitus and hyperacusis can exist separately or together. The study also validates ECochG as a sensitive tool for identifying cochlear nerve degeneration, moving diagnosis beyond the limited scope of the pure-tone audiogram. For a deeper look at how brain imaging differentiates similar conditions, our article on Misophonia vs Hyperacusis: Brain fMRI Differences explores related themes.

From a treatment perspective, the discovery of distinct neural gain sites provides new targets for intervention. Therapies designed to normalize activity in the cochlear nucleus may be more relevant for tinnitus, while those targeting later brainstem nuclei might be better suited for hyperacusis. Understanding this underlying nerve damage also reinforces the importance of auditory protection; preventing further cochlear nerve loss is a logical primary goal. The role of central gain in hearing disorders is further explored in our piece on the Cerebellum’s Role in Hearing Disorders.

Finally, this research underscores that “normal hearing” is more complex than a simple threshold test. It involves the integrity of the nerve and the brain’s calibrated response to that input. As Liberman noted, “We are now beginning to understand the biological basis for these debilitating conditions. The next step is to develop treatments based on these specific neural signatures.” For those seeking to manage their condition today, evidence-based approaches are reviewed in Tinnitus Counseling: A Scoping Review.

The study “Brainstem Correlates of Tinnitus and Hyperacusis in Normal-Hearing Listeners: Distinct Neural Signatures Linked to Cochlear Nerve Degeneration” was published in Ear & Hearing (2026). You can access the full paper via its DOI: 10.1097/AUD.0000000000001830 or its PMID: 42041197.