On sound and silence

Noise exposure can lead to elevated hearing thresholds and cause ringing in the ears (tinnitus) and hyperacusis, a condition in which normal sounds are being perceived as too loud. At present there are no treatments available that consistently cure tinnitus and hyperacusis, partly because the underlying mechanisms of these conditions are not yet completely understood.

In this thesis the neurophysiological consequences of acoustic trauma are studied. The balance between excitation and inhibition in the central auditory nervous system is disrupted as a result of acoustic trauma. This is in particular the result of a decreased inhibition in neurons that respond to frequencies below the trauma frequency. Furthermore, acoustic trauma causes an increased amplification of the signal in the brain. This was measured by auditory brain stem responses, as well as by neural responses to amplitude modulated sound.

The disrupted balance between excitation and inhibition, and the amplification of the signal in the brain may underlie neuropathology of tinnitus and hyperacusis. To investigate this, we propose a new method to demonstrate whether an animal experiences tinnitus or hyperacusis.

Our results may contribute to the development of an animal model in which a direct relationship can be established between the neurophysiological consequences of acoustic trauma and the presence of tinnitus or hyperacusis. Such an animal model is relevant for the development of new treatments.

Dissertation: http://hdl.handle.net/11370/a917ae29-647b-4a3f-9720-71b132e61663