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right, bilateral). Results have shown that differences in tinnitus laterality are reflected by different metabolic activity pat- terns in distinct nonauditory cortical regions. These results may help to develop new treatment targets for chronic tinnitus and to further individualize treatment strategies.

Metabolic activation of auditory cortex and inferior colliculi during salicylate-induced tinnitus in rats: A microPET imaging study. (Abstract of ARO Meeting Denver, Colorado) Asit Paul, Edward Lobarinas, John Luisi, Richard Simmons, Hani Nabi, Richard Salvi University at Buffalo

The purpose of this study is to investigate the metabolic activities in central auditory structures in vivo during salicylateinduced tinnitus in rats. The behavioral paradigm, schedule induced polydipsia-avo- idance conditioning (SIPAC), was first used to determine if tinnitus was present in rats treated with a high dose of salicylate. Following verification of salicylate induced tinnitus, a dedicated, high resolution animal positron emission tomography system (microPET Focus 120) was used to image the changes in brain metabolic activities associated with a high-dose of salicylate (250 mg/kg, i.p). In both the baseline and salicylate condition, rats were placed in a sound attenuating cubicle for 60 min after the injection of a ra- diolabeled glucose analog, F-18 labeled fluorodeoxyglucose (FDG, ~74 MBq, i.p). Thereafter, microPET scans of the rat brains were performed for 60 min in the prone position under isoflurane gas anesthesia. The frontal pole was considered as reference (control) area; FDG counts in frontal pole were expressed as a fraction of injected FDG dose per unit volume. Counts ratio between central auditory structures (auditory cortices, thalami and inferior colliculi) and frontal pole was used to compare between baseline and post-salicylate metabolic activity. The results show that the frontal pole FDG activity did not change between baseline and the post-salicylate condition, suggesting it as a metabolically inert area during tinnitus. During salicylate induced tinnitus, inferior colliculi (P=0.03) and auditory cortices (P=0.003) sho- wed significant increase in FDG activities, whereas there was no significant difference in thalamic activity (P=0.07) from the pre-salicylate, baseline state. Our study shows increased metabolic activity consistent with neuronal activation in inferior colliculi and auditory cortices during salicylate-induced tinnitus in rats (Supported by Tinnitus Research Consortium).

The neural code of auditory phantom perception. J Neurosci. 2007 Feb 7;27(6):1479-1484. Weisz N, Muller S, Schlee W, Dohrmann K, Hartmann T, Elbert T Department of Psychology, University of Konstanz, D-78464 Konstanz, Germany. weisz@lyon.inserm.fr

Tinnitus is defined by an auditory perception in the absence of an external source of sound. This conditi- on provides the distinctive possibility of extracting neural coding of perceptual representation. Previously, we had established that tinnitus is characterized by enhanced magnetic slow-wave activity (approxima- tely 4 Hz) in perisylvian or putatively auditory regions. Because of works linking high-frequency oscil- lations to conscious sensory perception and positive symptoms in a variety of disorders, we examined gamma band activity during brief periods of marked enhancement of slow-wave activity. These periods were extracted from 5 min of resting spontaneous magnetoencephalography activity in 26 tinnitus and 21 control subjects. Results revealed the following, particularly within a frequency range of 50-60 Hz: (1) Both groups showed significant increases in gamma band activity after onset of slow waves. (2) Gamma is more prominent in tinnitus subjects than in controls. (3) Activity at approximately 55 Hz determines the laterality of the tinnitus perception. Based on present and previous results, we have concluded that cochlear damage, or similar types of deafferentation from peripheral input, triggers reorganization in the central auditory system. This produces permanent alterations in the ongoing oscillatory dynamics at the

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