A molecular genetics study reveals an accessory olfactory-to-hypothalamic circuit in mice that optimizes defensive behaviors according to the imminence of predator threats.

The activation of defence brain circuits drives decisions to help conspecifics under threat.

Perceived imminence of threat and resulting intensity of defensive responses during serial compound stimulus conditioning are determined by auditory stimulus salience, not cue sequence as recently reported.

Associative and non-associative learning mechanisms summate to produce robust and complex conditioned behavior profiles, opening new avenues to in-depth investigations of defensive responses and threat evaluation.

Distinct dorsal periaqueductal gray ensembles encode threat approach and avoidance behavioral states.

The bed nucleus of the stria terminalis (BNST) is required for the expression of defensive behavior to uncertain threats, a function that is central to pathological anxiety.

Single-unit activity in the ventrolateral periaqueductal gray, a brain region implicated in organizing fear output, is found to reflect threat probability, a more versatile threat signal.

Comprehensive behavioral ethograms reveal a fear conditioned cue to elicit a temporally organized suite of behaviors spanning freezing, locomotion, rearing, and jumping.

Ventrolateral periaqueductal gray neurons signal fear output through patterned inhibition of neural activity.