Learning to Feel Safe: Different Rules, Different Molecules

Extinction of conditional fear is important both as a paradigm of inhibitory learning and as the explicit model for the development of behavior therapy for human anxiety disorders, including post-traumatic stress disorder. We have been studying the learning rules and the molecules that govern extinction of conditional fear in mice. We have found that unlike most forms of learning, extinction is more effective with temporally massed than with spaced exposures, perhaps because spaced exposures induce acute immediate increases of fear (incubation) that block extinction. Furthermore, extinction of conditional fear, but not its acquisition or expression, depends on L-type voltage-gated calcium channels. Finally, we have found that certain drugs appear to facilitate extinction in a variety of exposure protocols, apparently because they block incubation.