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INACTIVATION OF RAT AUDITORY CORTEX: EFFECT ON UNIT ACTIVITY IN VENTRAL MEDIAL GENICULATE P.G. Musial*; J.H. Wittig Jr; S.K. Talwar; G.L. Gerstein Dept Neurosci, Univ Pennsylvania, Philadelphia, PA, USA Acute inactivation of rat auditory cortex (AI) by the GABA-A agonist muscimol leads to profound impairment in pitch discrimination and tone detection (Talwar et al., 2001). This suggests that AI is normally essential for basic auditory functions although its detailed contribution remains unclear. The muscimol observations contrast with numerous former reports that animals with ablated AI perform pitch discrimination at normal thresholds. However, in those experiments the animals had a surgical recovery and retraining period so that plastic reorganization could take part in maintaining auditory function. AI sends massive feedback to the ventral medial geniculate (MGBv). The role of cortex could be only to maintain thalamic activity by tonic excitation rather than carrying out any computations. To investigate the feedback, we recorded evoked responses of MGBv neurons in anesthetized rats during inactivation of AI by muscimol applied on the cortical surface. In parallel auditory evoked potentials (AEP) were recorded from the AI surface. After inactivation of cortical activity all MGB neurons still responded to clicks and tones although firing rates of some neurons dropped by about 50%. The neurons maintained their response latencies and tuning properties with BF unchanged. Our finding suggests that AI functions in simple auditory tasks either by performing computations and/or conveying information to higher cortical areas. It is likely that there are alternate pathways to higher centers that are inaccessible during acute AI inactivation but may be recruited by plastic reorganization during recovery after ablation. Supported by: NIH DC 01249, MH 46428 Citation: P.G. Musial, J.H. Wittig Jr, S.K. Talwar, G.L. Gerstein. INACTIVATION OF RAT AUDITORY CORTEX: EFFECT ON UNIT ACTIVITY IN VENTRAL MEDIAL GENICULATE Program No. 354.6. 2002 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2002. Online.