Superior colliculus lesions impair threat responsiveness in infant capuchin monkeys.

The ability to react fast and efficiently in threatening situations is paramount for the survival of organisms and has been decisive in our evolutionary history. Defense mechanisms in primates rely on the fast recognition of potential predators and facial expressions of conspecifics. The neural circuitry responsible for the detection of threat is generally thought to be centered on the amygdala. Although it is a pivotal structure in the processing of emotional stimuli, the amygdala does not seem necessary for the early stages of this process. Here we show that bilateral neurotoxic lesions of the superior colliculus in infant capuchins monkeys impaired the recognition of a rubber-snake in a threat-reward conflict task. Lesioned monkeys were uninhibited by a snake in a food-reward retrieval task. Lack of inhibition in the task was observed over the course of 15 weeks. The long lasting recognition impairment of a natural predator observed here is similar to the tameness aspects of Kluver-Bucy syndrome, indicating an important role of this structure in threat recognition.