CHANGES OF SINGLE-UNIT ACTIVITY IN THE CATS AUDITORY THALAMUS AND CORTEX ASSOCIATED TO DIFFERENT ANESTHETIC CONDITIONS

Single unit spike trains were recorded in the auditory cortex (n = 78) and in the auditory thalamus (n = 55) of nitrous oxide anesthetized c ats. The electrophysiological activity was studied before and during t he application of pentobarbital (P, 7 mg/kg), ketamine (K, 12 mg/kg) a nd a mixture of these anesthetics (KP). The units were characterized d uring the spontaneous and acoustically driven activity ('white' noise and pure tone bursts). For the majority of cortical (61%) and thalamic (83%) units both drugs tended to decrease the spontaneous firing rate , but affected differently its time structure: P tended to increase th e average size of burst discharges, whereas K and KP tended to decreas e it. In the cortex the peak firing rate evoked by 'white' noise tende d to be decreased, whereas stronger excitatory responses were observed in the thalamus after injection of K or KP. The overall effect of the anesthetics during stimulation by pure tones was an increase in tonal selectivity due to a decrease in the response bandwidth. The response pattern to tones was also sometimes affected by the drugs. The direct evidence reported here for significant alterations of the discharge p roperties of auditory neurons in the thalamus and cortex resulting fro m low dose administration of K and/or P emphasizes difficulties in com paring data derived from experiments conducted in various conditions o f anesthesia or in the awake state.