Periodic Reporting for period 2 - LISTEN (Liaison in Scientific Training for European auditory Neuroscience)
Reporting period: 2018-12-01 to 2020-11-30
The LISTEN (Liaison In Scientific Training for European auditory Neuroscience) training network consisted of European auditory neuroscientists working with several European companies to improve hearing aids (including cochlear implants) and pharmacological treatments for tinnitus and hearing loss.
The overall objectives for LISTEN were:
1) To elucidate how the auditory system encodes complex sounds, both in normal and compromised hearing.
2) To study the underlying mechanisms of tinnitus, and test possible pharmacological treatments.
3) To train 10 ESRs to acquire technical skills and broader knowledge necessary in modern neuroscience research, while also learning to relate and translate their work for industrial and clinical applications.
The LISTEN project has led to new, fundamental insights into the question how the auditory system deals with the large range of sound intensities and sound frequencies it has to encode, how attention can modulate the encoding of the location of sounds, or the way the brain detects novel sounds. Moreover, mechanisms underlying different forms of hearing loss were elucidated, and some of the functional changes in the brain that occur in tinnitus were studied in detail. Finally, the LISTEN project has successfully trained 10 ESRs as auditory neuroscientists, which either have defended their thesis or are preparing to do so this year.
-To investigate how the inner ear encodes complex sounds a novel imaging technique called Optical Coherence Tomography (OCT) was established. This technique allows to study sound-induced movements in inner ear structures that were previously inaccessible. This technique allowed to define much better which structures in the inner ear are responsible for the decoding of complex sounds.
-To better understand how complex sounds are encoded in the brain, recordings from different auditory (inferior colliculus) and non-purely auditory (medial prefrontal cortex) regions were made. It was found that some cells can encode deviant sounds, i.e. sounds that had not been played in the recent history. These findings advanced in the understanding of the cellular mechanisms that allow discriminating changes in the environment, which are inaccessible in human research.
-The establishment of a technique that uses light to activate a defined set of auditory neurons in mice. This allowed to test to what extent optical stimulation can substitute for the auditory percept, leading to a better understanding of what an auditory percept constitutes. These studies therefore contribute to the scientific basis for the future development of prostheses based on direct activation of the central auditory system in hearing-impaired.
-a task has been designed that allows to study whether attention changes how the location of where sounds come from is encoded in the auditory cortex.
The second work package aims to study the underlying mechanisms of tinnitus, and test possible pharmacological treatments. Some of the examples of the progress obtained during the project are:
-A better understanding of the underlying cause for a form of progressive hearing loss in humans was obtained by studying the inner ear of a mouse model for this disease.
-A new method was developed to suppress the activity of potassium channels using light in a transgenic mouse. Potassium channels are very important for controlling excitability in neurons, and changes in excitability are thought to underlie tinnitus. This method will allow us to study the impact of potassium channels on excitability in a much more controlled way than by classical, pharmacological methods.
-Some of the cellular changes underlying tinnitus induced by high doses of salicylate, the active ingredient in aspirin, were characterized. These results can be used as the basis for studying the cellular mechanisms underlying other forms of tinnitus, including those that follow hearing loss.
-Several mouse models that showed unusual responses to sound, thought to be characteristic of the presence of tinnitus, were studied in detail, in order to better understand the underlying molecular and cellular changes. The observed abnormal responses to complex sounds give us insights that will allow a more precise diagnosis of different types of hearing impairments in humans.
An important part of this ITN has been devoted to training. Apart from a five-week summer course on Auditory Neuroscience, a large number of workshops were organized to train the ESRs in a variety of techniques and topics. An important part of the training involved secondments, in which new techniques and methods were learned from other laboratories within the LISTEN consortium. Each ESR did at least one secondment at another laboratory in an academic or industrial setting. The first scientific papers summarizing the results have already been published, and additional papers are in preparation. Most ESRs were able to present their results to the public and at scientific meetings, even though the Covid crisis led to the cancellation of all public outreach events that were planned in the final year and many scientific conferences.