Food and Intracranial Stimulation Responding Suppressed With Regular‐interval Shock

Abstract

Attenuation of conditioned suppression during intracranial stimulation was compared with that during food reinforcement. Response rates controlled by food and by brain stimulation were equalized on a multiple schedule by adjusting the stimulating current. When foot shock was delivered during timeout periods separating response components, responding for food was significantly more suppressed than responding for brain stimulation. When' components were shortened from 10 to 2 minutes, responding maintained by either food or brain stimulation showed a similar temporal pattern of suppression preceding each shock, but responding in the component involving food remained significantly more suppressed. Explanations for the attenuated suppression during brain stimulation based on neural disruption, stimulus blocking, and analgesic properties were questioned. The increased responding during brain stimulation seemed to reflect greater response strength relative to food reinforced responding.Key words: suppression, intracranial stimulation, shock, temporal discrimination, differential suppression, response strength, lever press, ratsResponse suppression during a brief conditioned stimulus paired with electric shock is the usual index of conditioned suppression (Estes and Skinner, 1941). Brady and Conrad (1960) noted a marked difference in suppression when intracranial stimulation (ICS) was compared to conventional reinforcers. Rats have typically failed to suppress responding during a conditioned stimulus (CS) with ICS as the reinforcer (Geller, 1970;Goldstein, 1966;McIntire, 1966). Merrill, Lott, and Bergen (1970) utilized procedural changes to discount several possible explanations for the attenuated suppression during ICS: neural disruption (Goldstein, 1966), blocked stimulus perception (Ball, 1967), resistance to distraction (McIntire, 1966), and analgesic effects (Breglio, Anderson, and Merrill, 1970). Russell (1975) reported that the intensity of the brain stimulating current was the determining factor, noting that response suppression was attenuated only with high-intensity ICS.The present study employed a variation of the traditional (Estes and Skinner, 1941) on the suppression of responding between, rather than during, the presentations of the CS and foot shock. A multiple schedule with alternating components of food and ICS reinforced responding was used, with presentation of CS and foot shock separating the components. The multiple schedule allowed a direct comparison of response suppression during food-and ICS-reinforced responding in the same animal. Nevin (1974) used a similar procedure to assess response strength under varying reinforcement conditions. He used multiple schedules with timeout periods, during which response-independent food deliveries were found to suppress component rates. Resistance to change in response rate was identified with response strength. Similarly, in the present study, differential response suppression could be identified with differential response strength for food-and ICS-reinf...