David A X Nayagam
B.Sci.(Neuro) / B.Eng.(Elec)(Hons.)

Postgraduate Research Student
Dame Elisabeth Murdoch Scholar

The University of Melbourne - Department of Otolaryngology
2nd Floor, Royal Victorian Eye & Ear Hospital
32 Gisborne Street
East Melbourne VIC 3002
Australia
Ph: +61 3 9929 8462
Fax: +61 3 9663 1958
E-mail: d.nayagam@pgrad.unimelb.edu.au

David Nayagam is a PhD student enrolled through the University of Melbourne and funded by the Dame Elisabeth Murdoch Scholarship administered by the Bionic Ear Institute. His supervisors are Dr. Tony Paolini, Dr. Janine Clarey, Dr. Anthony Burkitt and Prof. Graeme Clark.

The current project, conducted as a basis for David’s PhD thesis has investigated a brainstem region that is important in a pattern recognition pathway from the cochlear nucleus to the midbrain. This region - the ventral nucleus of the lateral lemniscus (VNLL) - receives input from a small but distinct area of the cochlear nucleus (the first processing point for signals from the inner ear) that is known to be sensitive to the onsets of broadband sounds and amplitude modulated (AM) signals. There has been relatively little research of the VNLL, so David’s work has first sought to describe this region in terms of its functional organisation and response properties to simple sounds. He has generated 3-D maps of the VNLL to examine its frequency organisation, the distribution of different response types, and whether cells response to only one or both ears. He has correlated physiology with morphology by filling cells with a dye after intracellular electrophysiological identification of a given cell. Experiments have also investigated the responses of these neurons to AM tones. He has found that many of the VNLL cells respond to AM signals with responses that are locked to the modulation frequency. In simple terms, this means that these cells are in effect ‘demodulating’ AM stimuli in much the same way as an AM radio would. This feature extraction may be important in processing human speech, which contains AM components. One of the novel findings from this project is a subset of VNLL cells that receive fast inhibitory inputs before showing an excitatory response to pure tones. As there are no known incoming inhibitory signals that could account for this finding, a network within the VNLL that rapidly converts incoming excitation into powerful onset inhibition is the favoured explanation. As an outcome of this proposed network, the origins of certain response patterns both in the VNLL and the midbrain may be resolved. These findings have recently been published in the Journal of Neurophysiology.

Currently David is writing his thesis and preparing manuscripts, having completed the experimental phase of his project. He is also planning a trip to the United States in early 2006 to present his findings at an international conference as well as to visit several world leaders in his field.

On a personal note, David loves music - playing lead guitar in an awesome Melbourne rock band (http://www.diane-young.com). He also enjoys skiing, table tennis, SCUBA diving, hang-gliding, films, television and sleeping – especially sleeping.

Publications & Presentations:
Nayagam, D.A., Clarey J.C., Paolini A.G. (2005). "Powerful, Onset Inhibition in the Ventral Nucleus of the Lateral Lemniscus." J Neurophysiol 94:1651-1654.

Nayagam, D.A (2005) "Powerful, Fast Inhibition Controls Spike Timing in the Auditory Brainstem." 2nd Australasian Auditory Neuroscience Workshop. Invited Speaker.

Nayagam, D.A., Paolini, A.G., Clarey, J.C., Burkitt, A.N., Clark, G.M. (2005). "Powerful, Fast Inhibition Controls First-Spike Timing In The Auditory Brainstem." Proceedings of the Australian Neuroscience Society 16:P175.

Nayagam, D.A., Paolini, A.G., Clarey, J.C., Burkitt, A.N., Clark, G.M. (2004). “Functional Organisation of the Rat Ventral Nucleus of the Lateral Lemniscus.” Proceedings of the Australian Neuroscience Society 15:P167.

Nayagam, D. A., Paolini, A.G., Clarey, J.C., Burkitt, A.N., Clark, G.M. (2003). “Intracellular and Extracellular Responses of Single Neurons in the Ventral Nucleus of the Lateral Lemniscus.” Proceedings of the Australian Neuroscience Society 14:P265.

  Author: d.nayagam@pgrad.unimelb.edu.au    Last Updated:  Friday October 28 2005