Ears are built to listen to sounds from the world around us, but for some people, the sound comes from within. Tinnitus causes people to hear ringing or other noises in one or both ears or in their heads, even when there is no actual sound outside. While tinnitus is frequently associated with hearing loss, a substantial proportion of individuals with clinically normal hearing thresholds still experience it, and the underlying mechanism remains murky to scientists. A recent study investigated how brain network patterns change as tinnitus progresses from a new condition to a long-term chronic one in people with clinically normal hearing.
After recording the electrical activity in the brains of people with acute and chronic tinnitus, the researchers found that the two conditions have very different neurophysiological profiles. People with recent-onset tinnitus showed an imbalance between two important brain networks: the salience network, which detects salient or potentially threatening signals, and the executive control network, which supports attention and decision-making. The brain significantly increases its focus on the former while decreasing the latter’s activity. Those with chronic tinnitus showed much more balanced switching between these networks, meaning the brain began to adapt rather than worsen.
The findings are published in iScience.
Tracking shifts in neural networks
About 10% to 15% of adults worldwide live with the distressing neurological condition. Most studies looking into neurological changes associated with tinnitus focus on participants with hearing loss. This made it nearly impossible to tell whether the observed brain changes were caused by tinnitus itself or simply by the brain reacting to hearing loss.
In people with normal hearing test results, tinnitus often traces back to subtle inner-ear changes that standard tests can’t detect. It is driven by cochlear synaptopathy, in which connections between inner hair cells and auditory nerve fibers are lost. Along with phantom sounds, this can result in high-frequency hearing loss above 8 kHz, a range that regular tests don’t check. These small changes in the ear can lead to bigger changes in the brain, disrupting how key networks function when the condition is new and acute versus when it becomes chronic.
In this study, the researchers directly compared neurological changes at different stages of the condition in people with normal hearing. The team recruited 45 participants and divided them into three equal groups of 15: acute tinnitus, chronic tinnitus and healthy controls with no tinnitus. Brain activity was recorded using a 64-channel electroencephalography (EEG) cap, which captured rapid, millisecond-long snapshots of the brain’s electrical activity. The researchers focused on four EEG microstate maps—Classes A, B, C and D—which correspond to the auditory, visual, salience and executive networks, respectively.
The collected data were then analyzed using dynamic functional network (DFN) analysis, which examined how effectively different parts of the brain within the microstates communicated and at what speeds, or frequency bands, ranging from slow delta waves to fast gamma waves.
The team found that tinnitus is not a fixed condition but a dynamic process in which the brain reorganizes itself as the disorder progresses. During the early stage of tinnitus (less than 6 months), the brain is in a state of imbalance and hypervigilance. The salience network becomes more active, while the executive network becomes less active.
As tinnitus becomes chronic, the brain undergoes compensatory rebalancing to find a new normal. Its activity patterns become more stable over time, shifting from high-frequency activity to low-frequency waves (delta and beta bands) in the executive and auditory networks, thereby regaining control over the phantom sound experienced by those with the condition.
While standard static connectivity analysis found no differences between groups, the dynamic approach did, suggesting that tinnitus’s neural signatures are fleeting rather than constant. The study’s approach was able to glimpse how the brain reorganizes its networks in real time. The distinct signatures across tinnitus stages revealed in the findings not only offer new insights into the disorder’s underlying mechanisms but also could act as biomarkers to help clinicians distinguish recent-onset from chronic tinnitus and tailor care accordingly.