PSYCHOACOUSTIC AND ELECTROMAGNETIC PROPERTIES OF RESIDUAL INHIBITION AND TINNITU

[Emiliano]

Larry E. Roberts and Daniel J. Bosnyak

Department of Psychology, Neuroscience, and Behaviour, McMaster University, Hamilton, Ontario, Canada

Animals exposed to noise trauma show augmented synchronous neural activity in auditory cortical tonotopic regions affected by hearing loss. Diminished intracortical inhibition in this region may set the stage for synchronous network activity which develops when deafferented neurons begin to respond to input via their lateral connections, generating a phantom sound (tinnitus) that is perceived in accordance with the location of the neurons in the cortical place map. This hypothesis implies that tinnitus spectra and “residual inhibition functions” which relate tinnitus
suppression to the center frequency of masking sounds should cover the region of hearing loss in the audiogram. We confirmed these predictions in a baseline cohort of 90 subjects using three computer-based tools designed to assess the psychoacoustic properties of tinnitus. Research in progress indicates that masking sounds that give residual inhibition enhance the 40-Hz auditory steady state response in tinnitus but not in control subjects, suggesting a persisting inhibitory deficit in the region of the auditory core.

(Supported by CIHR and NSERC of Canada and the
American Tinnitus Association)