Tinnitus is the perception of noise or ringing in the ears. It is a common condition, affecting an estimated 15% to 20% of people. Tinnitus is not a disease, but rather a symptom of an underlying condition. While it may be associated with hearing loss or ear damage in some cases, the primary cause of tinnitus lies in the brain, not the ear. Research has shown that tinnitus is correlated with increased neural activity in several regions of the brain. Understanding what parts of the brain are involved in tinnitus is important for developing treatments that target the underlying causes.
The Auditory Pathway
To understand what parts of the brain are involved in tinnitus, it helps to first review how sound is processed in the auditory system:
- Sound enters the ear and causes vibration of structures in the inner ear, like the eardrum and bones of the middle ear.
- These vibrations are converted into neural signals by the sensory cells of the cochlea.
- Nerve fibers carry these auditory signals from the cochlea to the brain via the auditory nerve.
- The auditory nerve fibers connect to a region of the brainstem called the cochlear nucleus, which is the first relay station of the auditory pathway.
- From the cochlear nucleus, auditory signals are sent to the inferior colliculus, medial geniculate nucleus of the thalamus, and finally to the auditory cortex of the temporal lobe.
This pathway allows the complex processing and perception of sound. Abnormal neural activity at various points along this pathway is believed to contribute to tinnitus.
Auditory Cortex
One of the main brain regions involved in tinnitus is the auditory cortex, located in the temporal lobe. The auditory cortex plays an important role in processing sound and interpreting auditory perceptions.
Studies using neuroimaging techniques like EEG and fMRI have found that tinnitus is associated with elevated neural activity in the auditory cortex, even in the absence of external sound stimuli. This explains why the phantom noise of tinnitus can be perceived. The increased spontaneous firing of neurons in the auditory cortex may occur in response to reduced sensory input from the ear, for example due to hearing loss.
Treatments like transcranial magnetic stimulation, which suppress abnormal neuronal activity, have been shown to temporarily reduce tinnitus when applied to the auditory cortex. This provides further evidence that the auditory cortex plays a key role in tinnitus.
Other Cortical Areas
Beyond the auditory cortex, other parts of the cerebral cortex have been implicated in tinnitus:
- Frontal cortex – involved in attention processing; increased activity may reflect concentration on tinnitus perception.
- Parietal cortex – integrates sensory input; may be associated with the emotional response to tinnitus.
- Anterior cingulate cortex – involved in conflict monitoring and attentional control; may play a role in tinnitus distress.
Abnormal neural oscillations (brain waves) coordinated across a network of cortical regions are proposed to underlie tinnitus. Disrupting these oscillations may help treat tinnitus.
Subcortical Areas
Structures that lie below the cortex also exhibit changes in neural activity associated with tinnitus:
- Brainstem – hyperactivity identified in cochlear nucleus and inferior colliculus, possibly related to reduced sensory input.
- Thalamus – serves as a relay for sound between the cochlea and auditory cortex; may filter phantom signals.
- Amygdala – involved in emotional processing; linked to negative reactions to tinnitus.
- Striatum – may be associated with persistent awareness of tinnitus.
A Complex Neural Network
Based on neuroimaging studies, tinnitus appears to arise from dysfunctions in a neural network encompassing both auditory and non-auditory brain regions.
While the auditory cortex is a major hub, treating tinnitus likely requires addressing broader changes in neural activity involving sensory processing, attention, memory, and emotion regulation. No single brain center is responsible for tinnitus.
Causes of Tinnitus-Related Brain Changes
What leads to the abnormal brain activity associated with tinnitus? Some potential causes include:
- Hearing loss – reduces auditory nerve input, which may trigger compensatory changes in the central auditory pathway.
- Noise exposure – can damage hair cells in the ear, altering auditory signals to the brain.
- Aging – hearing loss and neural changes with age may make the brain more susceptible to tinnitus.
- Head/neck injuries – affects auditory nerve or inner ear structure and function.
- Neurodegenerative disorders – conditions like Alzheimer’s appear to be linked to a higher risk of tinnitus.
The common thread is that alterations in auditory nerve signals to the brain seem to trigger maladaptive responses in auditory processing regions, making the brain perceive phantom noise.
Treatments Targeting the Brain
Since the root cause of subjective tinnitus lies in the brain, emerging treatments directly target brain activity through:
- Sound therapy – using external sounds to retrain auditory processing and suppress tinnitus perception.
- Cognitive behavioral therapy – helps shift attention away from tinnitus and manage reactions.
- Biofeedback – helps identify and modulate brain wave patterns associated with tinnitus.
- Neurostimulation – techniques like transcranial magnetic stimulation and direct current stimulation modulate neuronal activity.
- Implanted devices -stimulate the auditory cortex or vagus nerve to alter neural circuits.
While no cure exists for tinnitus, understanding how the brain generates phantom sounds points to promising approaches for managing this troubling condition. Ongoing research on the neurological basis of tinnitus will hopefully fuel more targeted, effective remedies.
Conclusion
In summary, tinnitus arises from abnormal neural activity in central auditory pathways of the brain, not the ear itself. Regions involved include the auditory cortex, frontal, parietal and cingulate cortex, brainstem, thalamus, amygdala and striatum. Disrupted communication and coordination between this network of auditory and associative regions generates the phantom noise perception of tinnitus. Knowing the neurological basis facilitates treatments like sound therapy, neurostimulation, and cognitive behavioral therapy that target brain activity to provide relief from tinnitus. While further research is still needed, our deepening understanding of the brain offers hope to those suffering from this troubling auditory phantom.