Changes in direct cortical response during elaboration of conditioned defensive reflex

A classical conditioned defensive reflex to direct, electric stimulation of the cerebral cortex was elaborated in dogs. The conditional stimulus (CS) was provided by electric stimulation of the middle suprasylvian gyrus at 1 Hz. Electrocutaneous stimulation of a forepaw served as the unconditional stimulus. During elaboration of CRs changes in the direct cortical response (DCR) were studied by recording them on an ink-recording electroencephalograph and a cathode oscilloscope with the use of averaging and superimpositions. The composition of the DCRs depended on stimulation site and intensity. Prior to conditioning, the DCRs contained either 2-3 components or a series of positive-negative potentials which often filled in the entire interval (1 s) between the stimulating pulses. When the cortical stimulation had acquired defensive significance, DCRs with a series of late components filling in the entire inter-pulse interval became much less frequent. Concurrently, the amplitude of late DCR components decreased during exposure to the CS. During elaboration of CRs the frequency of late DCR components also increased. All those phenomena were more strongly marked during electrocutaneous stimulation of the forepaw. The character of DCRs was found to depend on the dog's state; when alert, with activated EEG, late DCR components were few in number and low in amplitude, while in a calm state with a predominance of slow rhythms, DCRs with a series of late components frequently occurred and usually had a large amplitude.