Neuropsychological and neuroimaging studies have suggested that the primate amygdala plays an essential role in processing the emotional valence and intensity of visual stimuli, which is necessary for determining whether to approach or avoid a stimulus. However, the neuronal mechanisms underlying the evaluation of emotional value remain unknown. In the present study, we trained male macaque monkeys to perform an operant conditioning task in which fractal visual patterns were associated with three different amounts of air puff delivered to the cheek (negative) or liquid reward (positive). After confirming that the monkeys successfully differentiated the emotional valence and intensity of the visual stimuli, we analyzed neuronal responses to the stimuli in the amygdala. Most amygdala neurons conveyed information concerning the emotional valence and/or intensity of the visual stimuli, and the majority of those conveying information about emotional valence responded optimally to negative stimuli. Further, some...