People with tinnitus hear a ringing even when there is no sound. The prevailing theory blames a malfunctioning auditory system. However, it seems that abnormalities in the brain's limbic regions, which determine which sensations are important and how they are experienced, may also be involved.
Josef Rauschecker and his colleagues at Georgetown University in Washington DC used functional magnetic resonance imaging to scan the brains of 22 volunteers, half of whom had tinnitus, while they listened to various sounds. Patients with tinnitus showed heightened activity in the nucleus accumbens — a key limbic region — when presented with sounds that matched the frequency of the 'ringing' in their ears. They also had anatomical differences in the ventromedial prefrontal cortex, another limbic area.
The researchers suggest that an abnormal limbic system elevates the perceived importance of the tinnitus sound or fails to suppress it, and that interactions between the auditory and limbic systems may be at the root of this disorder.
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Ringing in the brain. Nature 469, 269 (2011). https://doi.org/10.1038/469269a