The effects of pre-extinction stress vs. physical exercise on contextual retrieval and generalization

Exposure to stress hormones before extinction learning leads to strong and less context-dependent extinction memories. However, laboratory stress induction protocols have disadvantages, such as increases in negative affect. In this study, we investigated physical exercise as another stress hormone associated, but healthy and more positively experienced modulator of fear extinction memories. We compared the effects of a vigorous-intensity exercise intervention (treadmill running) and psychosocial stress before extinction training on later contextual retrieval and generalization. To this end, 120 (60 women, 60 men) healthy participants underwent fear acquisition training in context A on day 1, the exercise, stress, or control intervention followed by extinction training in context B on day 2, and a retrieval and reinstatement test in context A, B, and C on day 3. The stress and exercise intervention both significantly increased heart rate, salivary cortisol and alpha amylase levels compared to the control intervention. For both skin conductance responses and pupil dilation, fear acquisition was successful and fear responding decreased over extinction trials. The groups did not differ in fear responding during retrieval 24 h later, but psychosocial stress seemed to reduce fear renewal in a novel context. Moreover, exploratory analyses revealed that stress reduced the context-dependency of the extinction memory after reinstatement in men, whereas exercise reduced overall responding in the extinction context. These findings shed light on potential boundary conditions of stress and exercise effects on contextual retrieval of extinction memories, including the generalization to novel contexts with high therapeutic value.