Threat imminence dictates the role of the bed nucleus of the stria terminalis in contextual fear

Previous work indicates that the bed nucleus of the stria terminalis (BNST) is involved in defensive freezing to unpredictable Pavlovian conditioned stimuli (Goode et al., 2019). Here we show that the BNST mediates freezing to contexts paired with remote (unpredictable), but not imminent (predictable), footshock. Rats underwent a fear conditioning procedure in which a single footshock unconditioned stimulus (US) was delivered either 1 (imminent) or 9 minutes (remote) after placement in the context; each rat received a total of four conditioning trials over two days. Contexts associated with either imminent or remote USs produced distinct patterns of freezing and shock-induced activity but freezing in each case was context-dependent. Reversible inactivation of the BNST reduced the expression of contextual freezing in the context paired with remote, but not imminent, footshock. Implications of these data are discussed in light of recent conceptualizations of BNST function, as well as for anxiety behaviors.