Experimental procedures affecting evoked responses recorded from auditory cortex

Abstract

1. 1. Four pairs of surface to deep-cortex electrodes were implanted in auditory cortex in each of six cats. 2. 2. Electrocorticographic recordings were taken from the electrodes before, during, and after all presentations of two types of acoustic stimuli: a 4 sec train cf clicks at 4000/sec used as the conditioned stimulus (CS) during conditioning, and a single click used as a test signal. For all animals there were at least six experimental sessions before the start ofconditioning sessions; two animals also received pseudo-conditioning sessions. 3. 3. The response evoked from auditory cortex of the unanesthetized preparation by an acoustic stimulus of abrupt onset is composed of a series of potential changes. As recorded in our experiments, the response contained four prominent deflections; a surface positive wave, followed in order by negative, possitive, and negative waves. A method was devised to describe the response by four amplitude measures. 4. 4. The cortical responses evoked by the CS and by the single click were similar in form and magnitude. 5. 5. Systematic changes in the evoked response were observed during the preconditioning sessions. 6. 6. Increases in the evoked response occurred during the pseudo-conditioning sessions. 7. 7. Unless preceded by pseudo-conditioning sessions, the evoked response typically increased during behavioral conditioning, 8. 8. The components of the evoked responses recorded from a given pair of electrodes were not necessarily affected equally by the various experimental procedures. 9. 9. During conditioning, changes in behavior preceded changes in the evoked response. 10. 10. No relation was noted between change in evoked response and particular sub-area of auditory codex in which the electrode was located. 11. 11. Increases in magnitude of the components of the evoked response during the first stages of preconditioning, during pseudo-conditioning, or during conditioning do not appear to be a direct consequence of the conditioning or learning process, that is, the learning of a leg flexion in response to an acoustic stimulus. A more likely interpretation is that the observed changes in the evoked response reflect complex changes in nlany neural structures, the latter changes being related to the emotional state and alertness of the experimental animal.