Paradigm structure and design considerations
Uncertain, shock
SHOCK
The Maryland Threat Countdown (MTC) is a well-established, fMRI-optimized version of temporally uncertain-threat assays previously validated using fear-potentiated startle and acute anxiolytic administration (e.g., benzodiazepine) in mice [The MTC paradigm (Valence was continuously signaled during the anticipation epoch by the background color of the display. Trial certainty was signaled by the nature of the integer stream. On Certain Threat trials, subjects saw a descending stream of integers (‘count-down;’ 30, 29, 28. . .3, 2, 1) for 18.75 s (0.625 s/integer). To ensure robust distress, this anticipation epoch always culminated with the delivery of a noxious electric shock, unpleasant photographic image (e.g., mutilated body), and thematically related audio clip (e.g., scream, gunshot). Uncertain Threat trials were similar, but the integer stream was randomized and presented for an uncertain and variable duration (8.75–30.00 s). Here, participants knew that something aversive was going to occur, but they had no way of knowing precisely 