An electroencephalograph study of classical conditioning

Abstract

Unanesthetized monkeys and cats bearing indwelling electrodes show electrical activity evoked by clicks and light flashes in regions such as caudate nucleus, hypothalamus, and limbic system as well as in the classically defined sensory pathways. Amplitude and duration of the evoked responses, which display a similar triphasic form wherever recorded, vary spontaneously but can be experimentally enhanced by reinforcement or reduced by extinction in a simple Pavlovian conditioning procedure. When an animal displaying large responses to click stimuli appears to attend to a simultaneous visual stimulus (distraction) the click-evoked activity is remarkably reduced. Both wave shape and lability of the responses are preserved despite paralysis produced by a curare-like drug and (at auditory cortex) cutting the auditory pathway bilaterally at the midbrain level. Relevance of these results to some previous studies on learning is discussed, along with the possible relationship of these data to the neurophysiological findings reported on anesthetized preparations.