Acute Exercise Modulates Fear Generalization And Extinction

Fear is an adaptive emotion which protects human beings from potential dangers.Fear generalization occurs while people respond to objects with similar feature to conditioned stimulus（CS）.Fear generalization is another important adaptive function that helps individuals giving prompt response to generalized stimulus（GS）which related to previously CS.However,over-generalization of safe stimuli to be a CS is the core symptom of anxiety disorders and of course will cause human problem giving extra cognitive burden to our daily life.In addition to the adverse effect of over-generalization to fear,the recurrence of fear extinction is another additional trouble to human beings and it ’ s also the core factor in the anxiety disorder therapeutically domain to uncover the mechanism of anxiety disorder recurrence.Repeated exposed the conditioned stimulus（CS+）in the absence of aversive unconditioned stimulus（US）to human,they will feel diminished fear emotion to CS+.However,fear extinction memory is unstable.One of the hottest topics is to find effective regulation methods to reduce fear extinction recurrence and over-generalization fear feeling at present,and it will enable to alleviate anxiety.A moderate-intensity treadmill exercise can have a positive impact on anxiety patients.Nevertheless,the effect of exercise on the fear generalization is ambiguous.Additionally,animal studies have shown that a voluntary exercise can enhance the consolidation of fear extinction memory in male rats,but the effect of acute exercise on human fear extinction recall as well as the cognitive neural mechanism behind it have not been fully discussed.This study first explored whether acute exercise had an impact on the fear generalization.Then,behavioral and functional magnetic resonance imaging（f MRI）was used to investigate the effect of acute exercise on extinction recall of fear and the neural mechanism.In experiment 1 we investigated whether the generalization process of fear was influenced by acute exercise.We used the classical fear-conditioning paradigm to explore the intervention effect of acute exercise on fear generalization,using the subjective expectancy and response time to GS as behavioral index.The results showed that acute exercise effectively inhibited the fear generalization The behavioral expectation scores showed the exercise group was significantly lower than that of the control group in the late stage.Experiment 2 investigated the effect of acute exercise on fear extinction recall and its neural mechanism.Consistent with experiment 1,we also used the fear-conditioning paradigm in experiment 2.Different from Experiment 1,we investigated both the physiological behavioral rating and neural mechanism in the process of fear extinction recall.We found that recurrence of fear in both groups without any group difference between two groups.In the initial stage of the fear recall test,the reaction time（RT）of CS + processing in the exercise group was significantly lower than that in the control group.f MRI results showed that there were also significant differences in the activation of brain regions induced by CS + between the two groups at this stage.Compared with the control group,the amygdala in the exercise group showed a lower activation state.That is,although there is no difference in the subjective expectancy between the two groups,the effect of acute exercise on the fear extinction exists at the neurological levels.Fear generalization is the main pathogenic mechanism of anxiety disorder.Fear extinction is the basic mechanism of exposure therapy for anxiety disorder.To unveil the mechanism of the influence of acute exercise on the fear generalization\extinction may be of great importance for the prevention and treatment of anxiety-related disorders.The results of this study suggest that the beneficial effect of acute exercise may be time dependent.Future studies need to further investigate the acute exercise effect of time..