Delayed conditioned reflexes were established in human subjects on the basis of the galvanic skin reflex (GSR) with an electric bell as a conditioned stimulus and with an induction shock as an unconditioned stimulus. The period of delay was fixed at 12 seconds. Changes in the pattern of electroencephalogram (EEG) were traced through the course of conditioning.
1. Prior to the commencement of conditioning, the conditioned stimulus alone was repeatedly applied so as to weaken its unconditioned excitatory effect. After the completion of this procedure, the conditioning was started by applying the conditioned stimulus in association with the unconditioned stimulus.
2. In response to the conditioned stimulus without associating the unconditioned one, there appeared two successive trains of excitatory waves consisting of repetitive spikes or of β and θ. The preceding train (the initial cortical excitation) appeared soon after the onset of the conditioned stimulus, while the succeeding train (the delayed cortical excitation) took place near the point of reinforcement. It is obvious in our experiment that these two sorts of cortical excitation represent the conditioned response of the cortex.
3. Just corresponding to the pattern of EEG, the conditioned GSR consisted of two. separate responses appearing in succession, i.e. the initial and the delayed GSR.
4. As the conditioning progressed, the initial response, central as well as peripheral, was gradually weakened. The delayed response which was developed more slowly than the initial one in the process of conditioning attained its maximal strength when the initial response began to deteriorate. At the final stage of conditioning, almost no initial response was seen, whereas the delayed response could still persist though greatly reduced in strength.
5. The conditioned GSR was discussed in comparison with the conditioned salivary reflex previously studied by us, and it was concluded that the GSR serves as a more faithful index of the cortical process than does the salivary reflex at least in human beings.
Our sincere thanks are due to Prof. K. Motokawa for his valuable advice during the course of this work.