EFFECTS OF AROUSAL ON AMPLITUDE OF EVOKED POTENTIALS

Using the stimulus conditions of classical defensive conditioning as the independent variables, the effects of arousal on EPs were followed. Five cats with implanted cortical and thalamic electrodes were trained in 3 phases: habituation, conditioning and extinction. The dependent variables, 1/sec photically-evoked responses were always present in the background. EPs occuring both before and during the CS were analyzed by a computer. Two control subjects, instead of having CS-US (tone-shock) pairing were exposed to an equal number of tone trials wtih shock presented randomly. Results showed that conditioning increased the amplitude of all EPs including pre-CS EPs and extinction attenuated all EPs. Onset of the tone did not significantly alter the morphology of the EPs even though a conditioned flexion reflex was formed. In control animals, no flexion reflex was formed and the amplitude of EPs was attenuated during 'situational conditioning'. During 'extinction' these EPs became even smaller. The results suggest that some EP amplitude changes observed during conditioning experiments might be due to the effects of a tonic activation associated with the total experimental situation rather than the immediate effects of the conditioned stimulus. © 1969.