Is there anybody out there? Neural circuits of threat detection in vertebrates

- Animals detect predators directly, use predator predicting cues, or cues from others.
- Alarm cues from meat digestion or injured conspecifics activate the olfactory system.
- The vertebrate optic tectum mediates defensive responses to visual looming stimuli.
- Movement-related auditory cues signal approaching predators or alarmed conspecifics.
- We propose the amygdala as site for multisensory integration of alarm cues.

Avoiding or escaping a predator is arguably one of the most important functions of a prey's brain, hence of most animals' brains. Studies on fear conditioning have greatly advanced our understanding of the circuits that regulate learned defensive behaviours. However, animals possess a multitude of threat detection mechanisms, from hardwired circuits that ensure innate responses to predator cues, to the use of social information. Surprisingly, only more recently have these circuits captured the attention of a wider range of researchers working on different species and behavioural paradigms. These have shed new light into the mechanisms of threat detection revealing conservation of the kinds of cues animals use and of its underlying detection circuits across vertebrates. As most of these studies focus on single cues, we argue for the need to study multisensory integration, a process that we believe is determinant for the prey's defence responses.