The effects of lateral, medial, or complete septal lesions on positive conditioned suppression in rats

This study investigated the effects of lateral, medial, or complete septal lesions in rats on lever pressing and US-approach behaviors during the presentation of a light followed by two free food pellets. Ten days after surgery, groups of rats received 20 sessions of a random interval (RI) 60-s schedule of food reinforcement. The positive conditioned suppression paradigm consisted of 20 sessions of a 10-s light paired with free food while the rats were responding on the RI 60-s schedule. All groups of rats significantly suppressed lever pressing during the 10-s light presentation. During the last four sessions of the 10-s light condition, rats with lateral septal lesions had a significant increase in food-tray entries during the light presentation, while the other groups decreased lever pressing without a change in food-tray entries during the 10-s light presentation. Although rats with septal damage generally have difficulty inhibiting responses in a variety of operant situations, rats with lateral, medial, or complete septal lesions showed no impairment in positive conditioned suppression. This study also suggests that when the spatial arrangement of the CS and the type of US were manipulated to minimize sign-tracking and goal-tracking behaviors, emotional reactions during the presentation of the CS must be considered a factor influencing positive conditioned suppression.