A shared threat-anticipation circuit is dynamically engaged at different moments by temporally uncertain and certain threat

Description: The Maryland Threat Countdown (MTC) paradigm is a well-established, fMRI-optimized adaptation of temporally uncertain-threat assays that have been behaviorally, pharmacologically, and psychophysiologically validated in rodents and humans. It takes the form of a 2 (Valence: Threat/Safety) × 2 (Temporal Certainty: Certain/Uncertain) repeated-measures, randomized event-related design. We capitalized on the temporally-extended threat-anticipation periods (8.75-30 s, mean = 18.75 s) of the MTC paradigm by modeling temporal dynamics in a more granular manner than before. For continuity with previous research, we performed an initial analysis using a single, variable-length rectangular input function (boxcar) for each anticipation epoch. In our theory-inspired model, we applied three input functions to each anticipation epoch: a brief, transient input function time-locked to anticipation epoch onset, an overlapping variable-length rectangular input function to model sustained activity spanning the entire anticipation epoch and a short, overlapping rectangular input function (6.15 s duration) time-locked to the terminal end of anticipation epochs to capture phasic surges during the ‘circa-strike’ phase. Each of the three input functions was convolved with a canonical HRF. For a second modeling approach, we took a piecewise approach to estimating BOLD magnitude in the temporal domain. For each anticipation period, 2-5 contiguous mini-blocks (6.25 s duration ‘boxcars’) were convolved with a canonical HRF. Findings point to a core neural ‘threat’ system that shows sustained activity across temporally uncertain threat and rapidly assembles in the face of certain-and-imminent threat.