Abstract
A delayed conditioned reflex was established in man with a metronome as a conditioned stimulul and with an electric light as an unconditioned one. The interval between the beginning of the metronome and the administration of the electric light was twenty seconds. Changes in electroencephalograms were studied in the course of the establishment of the conditioned reflex.
1. As the conditioning proceeded, cortical responses to the com-bination of the conditioned and unconditioned stimulus changed in a characteristic manner.
2. When the delayed conditioned reflex was completely established, the amplitude of α-waves increased at the onset of the metronome. In spite of the absence of the unconditioned stimulus the so augumented α-waves were suppressed and β-waves appeared at about the 20th second from the start of the metronome beats. The augumentation of the α-waves is an expression of the internal inhibition developed during the de-layed conditioned reflex, and the suppression of the α-waves and the ap-pearance of the β-waves represent the conditioned cortical excitation.
3. An extra-stimulus inhibited the effect of the inhibition induced by the conditioned stimulus and elicited a long lasting train of β-waves (disinhibition).
4. Experiments on generalisation, differentiation and experimental extinction were carried out when the conditioning was complete. After the differentiation or extinction had been established, it was found that a-waves were well developed in the whole extent of the oscillogram. This phenomenon must be attributed to the differential or extinctive inhibition.
5. The nervous mechanism underlying excitation and inhibition was discussed on the basis of experimental evidence.
