Table 2.

Comparison of safety signal learning and extinction learning

	Safety Signal Learning	Extinction Learning
Definition	The process through which a stimulus that is overly trained to signal the absence of threat (i.e., the safety cue) reduces, or inhibits, fear in the presence of a threatening cue. Safety signal learning is a class of conditioned inhibition.	The gradual process of fear reduction in classical conditioning that involves repeated exposure to the conditioned stimulus (CS) without the US.
Limitations	Safety cues may prevent the generalization of inhibitory learning (143,150,156,157,159), communicate threat, increase perception of threat, and direct attention away from information that is disconfirmatory during exposures (for a review, see 143).	Susceptible to relapse of extinguished fear (extinction memory does not overwrite the original fear association) via the mere passage of time (spontaneous recovery), exposure to a stressor (fear reinstatement), or return to a fear-associated context (fear renewal; for a review, see 206).
Key neural mechanisms	Ventral hippocampal connections with the PL in rodents and dACC in humans are hypothesized to be involved in inhibiting fear in the presence of safety (107). Dopamine receptors in the basolateral amygdala may also be involved in safety signal learning (207).	The amygdala, vmPFC, and hippocampus are central to fear learning and extinction (23,31-34) The infralimbic cortex in rodents and anterior vmPFC in humans inhibit fear expression and store and retrieve the extinction memory (54,113).
Age-related differences	Developmental studies are lacking. Hypothesized age-related differences such that safety signal learning may be augmented in adolescence.	Diminished fear extinction learning has been observed during adolescence across species (28,29).