Influence of pre-acquisition stress on fear learning and regulation as a function of sex and menstrual-cycle groups

Fear conditioning protocols are widely used to investigate fear learning and regulation, with clinical implications for post-traumatic stress and anxiety disorders. In real-world settings, fear learning often occurs under stress, affecting memory strength and regulation. However, laboratory findings on stress effects remain inconsistent, possibly due to the lack of consideration for sex and menstrual-cycle groups, given sex hormones receptors' abundance in fear- and stress-related brain regions. This study examined the impact of 1) pre-acquisition stress and 2) cortisol reactivity on fear processes across sex and menstrual-cycle groups (hormonal data unavailable). A total of 208 participants were exposed to a stressor (men (n = 24), women using oral contraceptives (OCs; n = 25), and women with a menstrual cycle in the early follicular (EF; n = 24) or late follicular phase (LF; n = 26)) or control condition (men (n = 29), OCs (n = 23), EF (n = 26), LF (n = 31)) before undergoing fear acquisition (Context A), where two colors were paired with shock (CS+) and another was not (CS-). On Day 2, one CS+ and the CS- were presented without shock (Context B) for fear extinction learning. On Day 3, extinction recall (Context B) and renewal (Context A) were tested, with all stimuli presented without shock. Fear responses were assessed by skin conductance responses (SCR) and self-reported shock anticipation. Stress-exposed participants showed lower SCR during fear acquisition than controls. During extinction learning, control men exhibited greater SCR reduction than stressed men, whereas LF women showed the opposite pattern. No group differences emerged during extinction recall. During renewal, stressed LF women had lower SCR to the CS+ than their control counterparts. Additional analyses suggested that stressed men with lower cortisol reactivity had higher SCR during fear acquisition and renewal than those with higher cortisol reactivity. These findings indicate that stress exposure and cortisol reactivity differentially influence fear learning and regulation across sex and menstrual-cycle groups, in a context-dependent manner.