Descending influences on central auditory function

Lead Research Organisation: MRC Institute of Hearing Research

Abstract

Hearing occurs when sound is transmitted through to the inner ear, converted into nerve impulses, and these are conveyed to and transformed by the brain. Problems with hearing (deafness) can occur in the ear or the brain. Listening pathways in the brain are of four types: (i) Information goes 'up' the system, from the ear to the cortex, the top part of the brain where consciousness occurs. (ii) Further processing in the cortex is influenced by other systems (e.g. vision, attention). (iii) Cortical messages influence 'action' (e.g. looking at a novel sound). (iv) The processed information also passes back 'down' the auditory system. Some of it gets right back to the ear, where it refines incoming signals. In this Strand, we are interested in this last, descending aspect of brain listening. Part of our work is exploring basic mechanisms of descending pathways - where do they go? What do they do? We are particularly interested in how these paths influence spatial listening; knowing where a sound is coming from. Other IHR research has shown how important spatial listening is to our overall listening experience, and how it contributes to hearing impairment. These and other IHR experiments are showing clearly that descending systems are even more influential than we had thought. They modify the activitity of almost all neurons in the up system and they seem to have effects at the level of the ear, possibly gating the way in which the ear responds to sounds. In children with poor listening skills ('brain deafness' or auditory processing disorder, APD), we have evidence that this gating may be malfunctioning. In other experiments, we are examining how descending pathways contribute to auditory learning, the improvement in listening with training. Auditory learning has great promise as an effective treatment for APD.

Technical Summary

Listening in children differs from that in adults. Children consistently perform more poorly than adults on a wide range of listening tasks. We are exploring the development of hearing between the ages of 3 and 12 years, with a focus on aspects of listening that may relate to auditory processing disorder (APD). Children who have normal hearing but poor speech perception in challenging situations are thought by audiologists to have APD. There are currently no UK standardised or scientifically validated tests to diagnose APD, although there is both a demand and uncertainty among the audiological community about how such children should be diagnosed, and an agreed definition of APD in audiology professional societies. Commonly used tests of APD are mainly speech-based, leading to confusion with language-based impairments, are poorly validated, and generally rely for their authenticity on people suspected of having APD. This programme aims to provide fundamental knowledge of the relation between hearing, listening, cognition, and the clinical presentation of what is termed APD. Translational aims are to develop a diagnostic test for APD and to contribute to the formulation of educational and health intervention strategies.

To test the specific hypothesis that the presenting symptoms of APD are related to a sensory processing deficit, we conducted a national, multicentre study of more than 1600 children of whom 1469 were normally hearing. We examined the ability of these children to perform a series of tone and noise listening tasks to assess their auditory spectral and temporal resolution, in terms of both response threshold (sensitivity) and response variability (an index of attention). We compared this auditory processing with tests of cognition (IQ, memory, language and reading), speech-in-noise, and parental assessments of communication and listening skills. The results indicated that measures of APD symptoms (speech-in-noise, communication and listening) were related to attention but not to sensory processing. We are currently involved in disseminating our results and negotiating several forms of commercial exploitation of the test battery.

We have engaged 25 audiology departments in the UK and 5 international research teams in the use of our test software (IHR-STAR) for various research and clinical purposes including diagnostic utility, comparison with other test procedures, use as a remediation tool, and assessment of the heritability of listening skills.

Publications

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Pilling M (2009) Auditory event-related potentials (ERPs) in audiovisual speech perception. in Journal of speech, language, and hearing research : JSLHR

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Palmer AR (2007) Some investigations into non-passive listening. in Hearing research

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Irving S (2011) Olivocochlear efferent control in sound localization and experience-dependent learning. in The Journal of neuroscience : the official journal of the Society for Neuroscience

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Bajo VM (2007) The ferret auditory cortex: descending projections to the inferior colliculus. in Cerebral cortex (New York, N.Y. : 1991)

 
Description Deafness Research UK Pauline Ashley Prize
Amount £5,000 (GBP)
Organisation Action on Hearing Loss 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2006 
End 03/2006
 
Description Corticocollicular influences 
Organisation University of Oxford
Department Department of Physiology, Anatomy and Genetics
Country United Kingdom 
Sector Academic/University 
PI Contribution Contributed to design of the studies, supervised the work of the first author, helped obtain funding, and contributed to write-up of research
Collaborator Contribution This work was initiated whilst the MRC researcher was still at the University of Oxford. Researchers there helped design these experiments and organized and executed every other stage of the research
Impact First demonstration of the role of a specific descending auditory pathway in a specific auditory function
 
Description Olivocochlear influences - Eaton Peabody Laboratory 
Organisation Harvard University
Department Harvard Medical School
Country United States 
Sector Academic/University 
PI Contribution Co-designed experiments, conducted experiments, analysed data
Collaborator Contribution Co-designed experiments, provided assistance in implementation, hosted a visit by a student
Impact Invited presentation to Gordon Research Conference 2008
Start Year 2006