In the developed world, hearing loss is the most common sensory disability, with around 15% of the population classified as deaf or hard of hearing.  This notwithstanding, exactly how we hear sounds – including how we identify biologically important acoustic signals such as speech and determine where they come from – is not currently well explained at a neurobiological level.

The primary focus of our research is on the functional organisation of the auditory cortex, which, despite decades of work, remains poorly understood.  There is some evidence for a division of labour within the auditory cortex, with certain regions being involved in extracting the location of the sound source while others are more concerned with its identity, but the interpretation of these studies remains controversial.  By adopting methods that have enabled exciting new discoveries to be made as to how areas of the brain responsible for vision and touch might contribute to behaviour, we hope to shed light on this debate by revealing how the firing of neurons in auditory cortex relates to the way in which we ‘hear’ sounds.

One of the most important discoveries in neurobiology in the last 15 years is the extent to which the mature cerebral cortex remains plastic, enabling perceptual abilities to be enhanced and new motor skills to be learned.  The study of the neurophysiological basis for perceptual learning is critical to our understanding of how biologically important information is represented and stored within the cerebral cortex.  A second phase of our work therefore involves investigating the location and nature of the physiological changes that take place within the auditory cortex as learning occurs on specific perceptual tasks.

As well as studying perceptual learning in individuals with normal hearing, we are investigating the role of experience and training in the capacity of the brain to adapt to altered inputs produced by the introduction of a reversible conductive hearing loss or by the restoration of auditory function by bilateral cochlear implantation or other neuroprosthetic interventions.

Current Research Programme

We use a multidisciplinary approach encompassing anatomical, electrophysiological, imaging, behavioural and computational techniques to study the neural basis for auditory perception.  We are investigating the cortical areas that are activated during auditory location, pitch or timbre discrimination tasks, the behavioural consequences of inactivating those areas or removing their projections, and the manner in which the tuning properties of their neurons evolve as behavioural performance improves in different perceptual learning tasks.

By carrying out a ‘neurometric’ analysis of the responses of the recorded neurons and comparing this with ‘psychometric’ data obtained from the behavioural measurements, we hope to be able to specify the physiological changes that are responsible for (and not just correlated with) behavioural performance.  These experiments will contribute to our understanding of how biologically important information is represented, coded and stored within the cortex, and will shed light on the current controversy concerning the extent to which different attributes of sound are processed within different cortical areas.

We are also investigating the locus and nature of the physiological changes that take place during training-induced adaptation to altered auditory inputs and stimulus-timing-dependent plasticity.  Having identified the neural networks that are reorganised in response to sensory experience and behavioural training, we hope to establish the rules that govern cortical plasticity and the cellular mechanisms responsible.  In particular, we are examining the role of multisensory experience and of the neuromodulatory inputs from the basal forebrain in mediating auditory cortical plasticity, as well as continuing our in vitro studies of visual-auditory integration in the developing midbrain.

Our perceptual learning paradigms are also being used to investigate the mechanisms underlying the capacity of the brain to recover basic functions that have been compromised as a result of peripheral impairments.  Our aim is therefore not only to improve our understanding of the plasticity of the brain, with its wider implications for the neurobiology of learning and memory, but also to use this information practically to stimulate new developments that will help to alleviate deficits in central auditory processing. 

With this is mind, we are developing, with colleagues in the ENT Department, an animal model of bilateral cochlear implantation, in order to track the physiological and behavioural changes that take place after auditory function is re-established following implantation at different ages.  By measuring performance on tasks that depend on stimulation of both ears, these experiments will also provide an opportunity to determine whether behavioural training can be used to promote the rehabilitation of hearing in previously deaf individuals.  In the future, we plan to extend this approach to examine whether chronic microstimulation of the midbrain might be a useful treatment strategy in individuals with peripheral hearing loss.

Further information can be found at: http://www.oxfordhearing.com

Andrew King