Advances in auditory neuroscience

We are pleased to serve as guest editors for this special issue of the International Journal of Psychophysiology that highlights exciting new advances in auditory neuroscience. Highly distinguished scientists have contributed reports of their work in the areas of development, pathology, auditory scene analysis, and the animal models that help clarify underlying neural mechanisms of sound perception. The compiled papers provide new insights into normal and aberrant sound processing occurring during development and in adulthood.

1. Development

Cone and colleagues utilized a novel approach of combining a standard behavioral measure of vowel discrimination in infants four–twelve months of age, using a head-turn paradigm in conjunction with neurophysiological measures. Using this approach, they demonstrated a significant correlation between perception and neurophysiologic discrimination. Shafer and colleagues extended the physiologic inquiry into older children, demonstrating developmental changes in the obligatory responses to vowel sounds in children from three months to eight years of age. Bruneau and co-workers examined the normal development of the understudied auditory evoked t-complex emanating from radial sources of auditory cortex located over the lateral surface of the superior temporal gyrus. They found a biomarker of right-ear/left hemisphere advantage in children with normal hearing. Together, results of these studies offer the exciting prospect of using electrophysiological biomarkers as a means to investigate the development of normal and aberrant speech perception. This prospect is highlighted in the work of Hamalainen et al., who present electrophysiological data demonstrating differential sound processing in young school-aged children with risk factors for dyslexia compared to age-matched controls. Similarly, Dr. Sussman and colleagues provide behavioral and electrophysiological evidence of a delayed developmental trajectory for complex sound processing in children with developmental language disorders compared to their age-matched peers.

2. Pathology

Moore continues this special issue’s inquiry into sound processing pathology and tackles the difficult problem of identifying mechanisms underlying “auditory processing disorder.” The importance of considering both bottom-up and top-down mechanisms and their dysfunction in this disorder is emphasized, as well as the need to incorporate newer technology such as genetic sequencing and MRI. The effects of deafness and resultant cortical reorganization is highlighted in the review paper by Sharma et al., who examine modulation of auditory cortical potentials in children fitted with cochlear implants, and cross-modal plasticity. Baldeweg and Hirsch compared elicitation of the mismatch negativity (MMN) component of event-related brain potential (ERP) in healthy controls with patients diagnosed with schizophrenia, bipolar disorder, and probable Alzheimer’s disease. Remarkably, they found that the MMN memory trace was diminished only in the schizophrenia group. The authors proposed that abnormal modulation of NMDA receptor-dependent plasticity was responsible for the deficits observed in patients with schizophrenia, and suggest that MMN may serve as a reliable biomarker for detecting the prodromal phase of this disorder. Effects of extrinsic factors on auditory evoked potentials were investigated by Stevens et al., who demonstrate that basic aspects of auditory cortical processing in children were impacted by the socioeconomic status (SES) of the household.

3. Auditory scene analysis

Alain et al. review the importance of voice as a memory cue in listening situations that involve noise and multi-talker babble. Difficulty with sound perception in such complex auditory environments is a common feature of normal aging. Rimmele and colleagues review current research in this population, and highlight the importance of temporal processing in auditory scene analysis, and associated sensory memory and speech perception. The importance of selective attention in modulating auditory cortical activity, while subjects listen to competing sound streams, was reviewed by Simon. He emphasizes that selective attention acts differentially, boosting the gain on the attended sound stream, and diminishing cortical activity elicited by the unattended stream. Sustained attention (vigilance) was examined by Nourski and colleagues, who measured high gamma activity recorded directly from auditory cortex in patients undergoing surgical evaluation for intractable epilepsy. The authors demonstrated that responses to target sounds were increased when compared to the same sounds when they were non-targets or presented during passive listening. They further showed that increased responses to target sounds were related to the task, and not to specific stimulus characteristics.

4. Animal studies

Animal models provide essential methods for clarifying neural mechanisms of hearing. Temporal processing of sound streams, a fundamental component of audition, is reviewed by Eggermont to elucidate processing mechanisms from the periphery to cortex. Complex auditory environments were studied in the works of Bee and Cohen. Bee illustrates how comparative studies of different species reveal an evolutionary diversity of underlying mechanisms for solving communication problems encountered when there are multiple competing background sounds. Cohen and colleagues review evidence suggesting how transformations of low-level sensory information along the auditory pathway relate to the perception of auditory events in complex auditory environments. Their review emphasizes how sound object formation and subsequent categorization are mediated by non-primary auditory cortex localized to the ventral stream, whereas behavioral decision-making is determined by activity further downstream in ventral–lateral prefrontal cortex.

We would like to thank the Editor-in-Chief, Connie C. Duncan, for inviting us to compile this special issue. We also would like to thank the many reviewers who contributed their time, expertise, and insights in assessing the manuscripts. We hope that the papers comprising this issue will excite the readership and inspire ever more sophisticated inquiries into these topics that will further illuminate our understanding of how the brain represents the complex auditory scene.