Conditioned Responses of Hippocampal and Other Neurons 1

Previous studies of neuron changes during conditioning have involved either surgical and paralytic restraints (Yoshii and Ogura 1960; Kamikawa et al. 1964) or free behavior in chronic animals (Buchwald et al. 1966; Travis and Sparks 1967; Ellison et al., in press). The search for neural traces of critical changes in learning has thus been clouded by the surgical and paralytic procedures or confounded by the correlates of the new conditioned responses. There has also been confusion resulting from the sensitizing effects of the unconditioned stimulus (US) and from changes in attention level which occur as the conditioned stimulus (CS) becomes a sign of a more or less significant unconditioned stimulus. New techniques have permitted us to study conditioned neuron responses that were not correlated with new skeletal movements or with changing states of sensitization or arousal in animals that were neither anesthetized nor paralyzed. Our object was to obtain evidence which might implicate structures of the hypothalamohippocampal system in temporary information storage and in anticipatory or other internal responses divorced from immediate skeletal and arousal patterns. Interest in the hippocampus and its related subcortical structures stemmed from several kinds of experiments which related it in one way or another to temporary information storage. There were first the observations indicating a failure of some informationholding functions in humans after hippocampal