Central but not basolateral amygdala mediates memory for positive affective experiences

Rats were trained in an 8-arm radial maze on a task in which memory for magnitude of reinforcement was tested. Rats received a single trial per day consisting of a study phase and a test phase. In the study phase, the animals received 1 or 7 pieces of food on different arms of the maze. After the study phase, the rats were delayed for 5 s, 5 min or 15 min. After the delay the animals were allowed to choose between the two arms presented in the study phase. The correct response, leading to an additional reinforcement, was to select the arm in which the animal had received the 7 pieces of food. After learning this task to a criterion of 80% or better performance on blocks of 10 trials for each delay, the animals received electrolytic lesions of the basolateral or central amygdala. After recovery from surgery animals were tested at each delay. The results indicate that there were no deficits at any delay with basolateral amygdala lesions. In contrast, lesions of the central amygdala produced a marked deficit at the 5- and 15-min delays, but no deficit at the 5-s delay. Based on the assumption that in this task memory for magnitude of reinforcement is a function of the formation of reinforcement-spatial location associations resulting in the activation of affective experiences, it is concluded that the central but not basolateral amygdala is involved in the coding of positive affect information.