The influence of exercise on persistence of fear
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Pavlovian fear conditioning has been used for almost a century to better understand how fear is acquired and remembered, as well as to find ways to augment the learning and memory process to change memories and create new competitive memories, in an investigation to reduce the persistence of fear. The current work set out to determine if acute and/or chronic exercise could reduce persistence of fear. First, after early life fear exposure (at post-natal day 17 [P17] or 25 [P25]) rats were given a chronic regimen of exercise during late adolescence to determine if exercise could influence memory recall or fear learning (or re-learning) in adulthood. Results indicate a difference in memory based on age of fear exposure, such that rats conditioned at P25 but not P17 show increased levels of freezing when tested in adulthood. While P17 conditioned rats, do not show a fear memory, increases in the average distance run did predict less freezing during the retention test, suggesting an influence on generalized anxiety rather than fear memory directly. Conversely, irrespective of early P25 condition, exercise produced a similar negative correlation on the fear response after adult fear learning; such that increased distances run predicted lower levels of freezing. Following these tests of chronic exercise, acute 30-minutes and 3-hours of exercise prior to extinction/exposure were shown not to enhance reductions in fear on either long-term memory or fear relapse tests, for neither cued nor contextual fear paradigms. Finally, a meta-analytical approach was employed to disentangle when and under what conditions exercise could enhance fear extinction, but also its influence on other Pavlovian and operant extinction models within the literature. Results indicate that exercise significantly enhanced reductions in responding for operant but not Pavlovian models, with different moderators under both models. Interestingly, it was found that exercising after Pavlovian extinction was critical to larger reductions in responding over extinction alone, which may account for the lack of enhancement seen in my previous findings. Taken together the potential for exercise to reduce the persistence of fear may depend on the timing of application and whether you’re targeting learning or memory.