INTRODUCTION: Social support during exposure-based psychotherapy has been suggested to have an important influence on the course of exposure treatment, however some clinical trials show that individual therapy may be more effective than group therapy. The mechanisms of social influence on fear extinction remain unknown. METHOD(S): To study neuronal correlates of social buffering in fear extinction, we have developed a rat model. In our model, rats showed a significant lowering of fear response during fear extinction when exposed to fear‑associated stimuli with a companion. The buffering magnitude depended on familiarity and physical similarity of the tested animals but not on their emotional status; the fear‑conditioned partners were as effective as naïve ones. However, the effect was transient and disappeared when rats were tested individually the next day. To test whether social buffering shares neuronal mechanisms with fear extinction, we measured activation of fear regulating neuronal circuits. Lower fear response during exposure with a partner was associated with lower activation of the infralimbic (IL), prelimbic (PL), and anterior cingulate (ACC) cortices. However, although optogenetic blocking of the IL increased fear response in rats tested separately, it left the social buffering effect intact. RESULTS: Analyzing inputs to the cortex from the ventral hippocampus (vHIPP) and basolateral amygdala (BL), we found significantly more vHIPP innervated neurons activated in the PL but not IL or ACC of the socially buffered rats. CONCLUSIONS: The results show that fear memory suppression by the presence of a companion is transient and relies, at least partially, on different neuronal circuits than fear extinction.
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