Fig. 1: Experimental timeline, task overview, and histological assessment of cannula placements.

a Experimental timeline. All marmosets (n = 7) were first habituated to the testing apparatus so the context became affectively neutral, after which sgACC/25 infusions were carried out in this neutral condition to assess basal cardiovascular changes. Next, marmosets underwent infusions on the conditioned threat and extinction (n = 4) and aversive Pavlovian discriminative conditioning (n = 7) paradigms (see Table 1 for details). Human intruder (HI) testing (n = 7) was interleaved with aversive discrimination testing. Finally, four marmosets underwent ¹⁸F-FDG PET scanning. b In the neutral condition, no CSs were presented. c In the Pavlovian conditioned threat and extinction paradigm, habituation occured over the first two days; learning of the CS (auditory cue)-US (rubber snake) association occurred over the third acquisition day; and on the subsequent extinction and extinction-recall days (days four and five), the cue was presented without the snake. d In the aversive Pavlovian discriminative conditioning paradigm, marmosets learned to distinguish between a threatening auditory cue (CS+) predicting aversive white noise and darkness (US+), and a safety auditory cue (CS−) predicting a neutral tone (US−). e Histological assessment of cannula placement using cresyl-violet staining. No damage was noted in any animals aside from the small area of gliosis used to pinpoint cannula placement. A schematic diagram, left, shows the cannula placement for all marmosets reported in the manuscript (anteroposterior [AP] extent between +12.5 and +13.8 mm from interaural line, diagram centered around +13.0mm) together with the estimated spread of infusion in gray (0.5–1.0mm). A representative cresyl-violet stained histological section is shown right, with the cannulation site indicated by an arrow.