Auditory cortex 2014 – towards a synthesis of human and animal research.

Abstract

From September 13 to 17, 2014, more than 270 auditory neuroscientists from 24 countries gathered in Magdeburg (Germany) for the 5th International Conference on Auditory Cortex (www.auditory-cortex.de), which was hosted by the Leibniz Institute for Neurobiology in Magdeburg. This conference continued a series of previous conferences held in Magdeburg in 2003 and 2009, in Grantham (UK) in 2006, and in Lausanne (Switzerland) in 2012. This Special Issue of the European Journal of Neuroscience (EJN) brings together 17 peer-reviewed papers nearly all based on invited talks presented at this meeting. The abstracts of all 200 contributions (40 invited speakers, 160 posters) can be found in the “Proceedings of the 5th International Conference on Auditory Cortex – Towards a Synthesis of Human and Animal Research” (Budinger, 2014). Sometime in 2002, Henning Scheich, one of the most influential contemporary German neuroscientists and founding director of the Leibniz Institute for Neurobiology in Magdeburg, expressed the idea that it was about time to bring together scientists working on the auditory cortex of humans with those working on that part of the brain in animals. An international meeting would enable these scientists to learn and benefit from each other's knowledge and experience by exchanging concepts, approaches, and thoughts. The researchers studying the human auditory cortex, mainly using non-invasive techniques such as functional magnetic resonance imaging, magneto- and electroencephalography, often seemed rather unaware of the progress made by the researchers studying the auditory cortices of animals, mainly using invasive anatomical and physiological methods; and vice versa. Henning Scheich's idea fell on fertile grounds and, after a short survey among several local and outside experts, the ICAC was born. In 2003, more than 200 participants from all over the world attended the first ICAC in Magdeburg, hosted by the Leibniz Institute for Neurobiology. Taking up Henning Scheich's idea, it consequently carried the subtitle “Towards a Synthesis of Human and Animal Research”. The conference agenda covered three main themes: (i) auditory cortical fields and their functions, (ii) coding of sounds, and (iii) plasticity, learning, and cognition (Budinger & Gaschler-Markefski, 2003). The presentations of the 35 invited talks and more than 100 posters were excellent, the discussions were lively, and the social events facilitated the communication between the participants. The scientific outcome resulted in the publication of the 500-page book “The Auditory Cortex – A Synthesis of Human and Animal Research” (König et al., 2005). The success of this first conference triggered a second one; in fact, it started a series. In 2006, the second conference took place in Grantham, east of Nottingham (UK). It was organized by Dave Moore, Alan Palmer, Deborah Hall, Chris Sumner, Lisa Fretwell, Angie Killoran, and colleagues of the MRC Institute of Hearing Research. The meeting was subtitled “The Listening Brain” to indicate both the importance of active engagement with acoustic signals, an issue that has already emerged from the 2003 meeting, and the advances that had been made in understanding the role of the auditory cortex in “active hearing” or “listening”. Some 160 participants discussed the 20 invited talks and 80 posters, which covered three main topics: (i) the distributed, (ii) the computational, and (iii) the cognitive auditory cortex. Papers related to these and other topics of the conference appeared in a Special Issue of Hearing Research (see Moore et al., 2007). Returning to Magdeburg, the subtitle of the 2009 conference “Current Concepts in Human and Animal Research” again reflected our main goal: to bring together scientists who study the auditory cortex in humans with those who study it in animals. The conference was arranged around five sessions comprising 33 invited talks: (i) how to define auditory cortex, (ii) coding principles in the auditory cortex, (iii) the adaptive auditory cortex, (iv) processing of vocalizations, speech, and music, and (v) functional circuitry in the auditory cortex. During a round table discussion, seven renowned experts contrasted concepts of auditory functions together with 200 attendees. About 120 posters, some also advertised in short oral presentations, completed the scientific program. A collection of papers based on the invited talks of the conference was again published in a Special Issue of Hearing Research (see Brechmann et al., 2011). In 2012, the scientific organizers of the fourth conference (Daphne Bavelier, Stephanie Clarke, Jonathan Fritz, Troy Hackett, Andrew King, Micah Murray, David Poeppel, Shihab Shamma, Mark Wallace) in Lausanne (Switzerland) decided arranging the meeting on the basis of submitted proposals for scientific symposia. The five proposals winning the competition were: (i) integrating behavior and neurophysiology, (ii) dynamic spatial processing in the auditory cortex, (iii) shedding light on auditory cortex, (iv) computational principles of auditory cortex, and (v) perceptual operations and underlying mechanisms in the primate auditory cortices. These five symposia comprised 23 talks and were complemented by a graduate students' award symposium, a moderated (heated) debate, and about 170 posters. In March 2015, some of the contributions will be available as papers in a Special Issue of Brain Topography (Vol. 28/2). In order to avoid temporal overlap with the International Symposium on Hearing, it was agreed upon to deviate from the 3-year interval and to hold the fifth meeting already in 2014, again in Magdeburg (see below). In 2017, the 6th ICAC will take place in Banff (Canada), and it is organized by Stephen Lomber from the University of Western Ontario (Canada) and Yale Cohen from the University of Pennsylvania (USA). It is planned that three years later the conference will return to Magdeburg. The subtitle of the 5th International Conference on Auditory Cortex was again “Towards a Synthesis of Human and Animal Research” because of the continued need to join the two fields. The scientific program reflected current topics studied in both fields and was arranged around the following six sessions: (i) auditory cortex in different species, (ii) the hearing action cycle, (iii) auditory cortex: it's about time, (iv) auditory cortex: clinical aspects, (v) multisensory interplay in auditory cortex, and (vi) learning in auditory cortex. Invited speakers from each of these sessions agreed to contribute to this Special Issue of the EJN. Their papers are reviews, opinions as well as original research based on the presentations at the meeting; however, they also elaborate beyond what was presented there. Studies of the anatomical and functional organization of auditory cortex in different species (topic i) and its role in communication and behavior help to identify common underlying principles of auditory cortex functioning and to distinguish them from species-specific specializations owing to particular needs and evolutionary traits. They also emphasize the value of neuroethological approaches for understanding auditory behavior, including vocal communication. Kössl et al. evaluate in which respect the processing modules of bat auditory cortex can serve as a model for typical mammalian auditory-cortex function or are suited for purposes unique to the demands imposed by echolocation, such as estimating range from echo delays. Wallmeier et al. explore the role of auditory and visual cortex in humans during echolocation tasks. Their fMRI data show that early-blind echolocation experts and sighted, echolocation-trained control subjects, recruit different cortical areas for the same active-echolocation task. Elie & Theunissen investigate the neural representation of the semantic categories of zebra finch vocalizations within primary and secondary auditory cortical areas, showing that computations necessary for semantic categorization of meaningful vocalization are present in the avian auditory cortex. Wilson et al. used rule-based sequences of sounds, with local and longer-distance relationships, to study artificial grammar learning in nonhuman primates and in humans. Their results suggest that the required sequence-processing computations may not be unique to language-possessing humans. Rauschecker argues that an improved understanding of auditory cortical processing can be obtained by comparison to visual cortical functioning, on both a level of neural mechanism and of processing pathways for the identification of objects and the processing of space. Furthermore, expanding this idea in terms of sensorimotor integration and control would provide an overarching view of cortical function independent of sensory modality. When we hear sounds we may decide to orient and act towards the location from where the sounds originate. When we move we frequently generate sounds, and we use sounds to guide and control our movements and actions. The interrelationships between sounds and actions have recently come into the focus of interest of researchers of auditory cortex. They complement recent research on the representation of non-auditory aspects of auditory tasks in auditory cortex. They also complement the notion that auditory cortex functions as a “semantic processor” deducing the task-specific meaning of sounds. In this Special Issue, we were able to attract two groups of authors (Merchant et al. and Brosch et al.) to contribute articles to aspects of this hearing-action cycle (topic ii). Time is most essential (topic iii) for processing of auditory-related information. Neurons in the auditory cortex are sensitive to aspects of sounds on multiple time scales, from a few milliseconds up to several seconds. In this way, neurons possibly encode the complexity of past auditory stimulation, and this attribute may also play a crucial role in the prediction of upcoming auditory events. Issues derived from studies on humans and animals and related to the representation and the relevance of time comprised stimulus specific adaptation, temporal structure of sound sequences, cortical dynamics of speech perception and language comprehension, inhibitory networks and functional processing of spectral and temporal response features, temporal dynamics and spatial distribution of high gamma activity, and predictive processing. May et al. contribute a paper to this Special Issue, in which, based on computational modeling, the relevance of long-term synaptic adaptation for temporal integration in auditory cortex is addressed. Schroeger et al. review what can be learned from cognitive psychophysiology about prediction and attention in audition and discuss these two concepts in the framework of the predictive coding theory. König et al. scrutinize the averaging process in MEG/EEG research and emphasize that the common practice of subtracting arithmetic means of auditory-evoked waveforms is problematic. They encourage researchers to check which model (additive or mixed) underlies their data and to apply an appropriate transform, the asinh-transformation, if required. Apart from the gap between animal and human research, another gap needs to be bridged, namely that between fundamental and clinical research (topic iv). Three major clinical topics in auditory research are auditory-based language impairments, restorations of hearing by cochlear implants, and tinnitus. Here, Eggermont provides an overview of the achievements in tinnitus research both on animals and humans and importantly addresses the question about how predictions from animals models relate to findings in human cochlear implant users. Strelnikov et al. present results of a PET study on cochlear implant users that provide insights into experience dependent plasticity effects in audio-visual integration. Such research will hopefully arouse more interest in clinical aspects of auditory functions; both to transfer knowledge from basic research into the clinic and to better understand normal auditory processing. The problems of how the different senses merge in the brain and how the brain associates this information with behavioral demands have kept neuroscientists busy for several decades. Initially, research focused on “classical” multisensory brain structures like the superior colliculus and the parietal cortex; recent research also includes low-level cortical areas, previously deemed unisensory. In this Special Issue, authors from various fields of animal and human research present their scientific results and views on the role of the auditory cortex in multisensory processing (topic v). They emphasize, for example, specific functions of the different auditory fields and other brain areas in audiovisual and audiotactile integration processes, physiological mechanisms and anatomical pathways of multisensory integration at cellular and areal levels (Meredith & Allman; Brosch et al.), the role of single- and multi-trial learning (Matusz et al.; Brosch et al.) as well as short- and long-term musical training (Pantev et al.) on the neuronal processing of uni- and multisensory information, and mechanisms of cross-modal reorganizations following sensory impairment and restoration (Meredith & Allman; Strelnikov et al.). Quite generally, neurobiological research on learning (topic vi) has to bridge a categorical gap because learning is a phenomenon defined on the behavioral and psychological level. In auditory cortex research, the identification of potential neural mechanisms underlying specific alterations of behavior or psychophysical performance induced by learning has been particularly successful. In this Special Issue, authors (Bao; Perks & Gentner; Pantev et al.) report and discuss recent findings of physiological mechanisms underlying learning and learning-related phenomena on multiple levels, ranging from cellular physiology, via neural network dynamics and imaging results to particular behaviors in rodents, birds, and humans. We wish to thank the many sponsors of our meeting, most notably the Deutsche Forschungsgemeinschaft, the Office of Naval Research Global, the Magdeburg Center for Behavioral Brain Sciences, and, of course, the host of the meeting, the Leibniz Institute for Neurobiology Magdeburg; for a complete list of sponsors see www.auditory-cortex.de/sponsors.html. We are most grateful to Carola Kolouschek (Public Relations|Media|Events, Magdeburg) for the administrative organization of the conference, to the Herrenkrug Parkhotel for providing the outstanding ambience, and to all the people who provided a helping hand before, during, and after the conference (all listed under www.auditory-cortex.de/acknowledgements.html). We would also like to thank the authors and anonymous reviewers of the papers of this Special Issue and the EJN staff, in particular Sophie Gavarini, Julie Mion, Martin Sarter, and Jean-Marc Fritschy, who took all editorial handling and decisions, thus enforcing the timely publication of this Special Issue. Finally, we would like to thank all participants, for coming to Magdeburg to join the conference and contribute to its sessions; thus, filling the scientific as well as the social events with life. The scientific organizing committee and guest editors of this Special Issue of EJN: André Brechmann, Michael Brosch, Eike Budinger, Peter Heil, Reinhard König, Frank Ohl, and Henning Scheich. Magdeburg, December 23, 2014.