Tinnitus, i.e. the perception of phantom sounds in the absence of an acoustic stimulus, can be caused by hearing loss. Under which circumstances does this occur? Which mechanisms are involved? Roland Schaette and Richard Kempter from the Bernstein Center for Computational Neuroscience and the Humboldt University in Berlin found answers to these questions using computer simulations.
Tinnitus arises in the auditory pathway of the central nervous system. In animal studies, tinnitus-like activity of neurons - so-called hyperactivity - has been found in the dorsal cochlear nucleus (DCN), the first processing stage for acoustic information in the brain. Neurons of the DCN receive input directly from the auditory nerve and react to it with neuronal discharges - one says, they "fire".
Even without any acoustic signals, however, cells of the auditory nerve and the auditory pathway are still active and fire spontaneously at a certain rate, the "spontaneous firing rate" - comparable to the background noise produced by electrical devices. Various studies suggest that hearing loss can increase the spontaneous firing rate of nerve cells in the DCN and that animals perceive this as a kind of tinnitus. In a theoretical model, Schaette and Kempter explain the link between tinnitus and hearing loss for the first time.
After hearing loss, auditory nerve fibers and neurons along the auditory pathway only react to loud sounds. For soft sounds below the increased hearing threshold, the neurons fire spontaneously. Many neurons thus show an overall reduced activity. This could trigger a mechanism called "homeostatic plasticity", which ensures that neuronal activity is neither too high nor too low. If the average activity of the neurons is too low, homeostasis enhances their sensitivity. As the scientists could show in their model, neurons then react more strongly to the activity of the auditory nerve; in particular the spontaneous firing rate increases.
Moreover, Schaette and Kempter also demonstrated in their model that this mechanism only applies to certain types of neurons - for example to type III neurons of the DCN. These neurons are primarily activated by sound. Therefore, their average activity initially drops after hearing loss and the mechanism described above is initiated: homeostasis has to counteract this loss in activity and elevate firing rates, which then also leads to an increased spontaneous firing rate.
In contrast, type IV neurons are either activated or inhibited by sound, depending on sound intensity. Hearing loss only has a minor effect on their average activity. Accordingly, these neurons are less susceptible to hyperactivity. This prediction of the Berlin scientists' model corresponds with experimental findings: In rodents type III neurons dominate in the DCN. Here, tinnitus-like hyperactivity has been observed. In contrast, such an activity has not yet been found in cats, whose DCN mainly holds type IV neurons.
"Our studies have corroborated the association between hearing loss and tinnitus, which could provide a foundation for new treatment strategies," Kempter states. "Our hope would be that a tailored exposure to acoustic signals over an appropriate frequency range could help to drive back the hyperactivity caused by hearing loss".Original publication:
Schaette R, Kempter R: Development of hyperactivity after hearing loss in a computational model of the dorsal cochlear nucleus depends on neuron response type. Hear Res 240:57-72 (2008). doi:10.1016/j.heares.2008.02.006Contact:
Fingerprint' technique spots frog populations at risk from pollution
27.03.2017 | Lancaster University
Parallel computation provides deeper insight into brain function
27.03.2017 | Okinawa Institute of Science and Technology (OIST) Graduate University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
27.03.2017 | Earth Sciences
27.03.2017 | Life Sciences
27.03.2017 | Life Sciences