Study Of Comparison Between Conditioned Fear And Innate Fear Elicited By Looming Stimulus

Fear is referred to behavioral and physiological responses elicited in animals by danger,which is necessary for the survival of the individuals and can be observed in virtually all animal species.It is generally considered by neuroscientists that the neurobiological foundation of fear can be multiple neural circuits mediating fear responses.Although both conditioned fear and innate fear belong to fear,because of the limitation of design of behavioral paradigm and the inconsistence of neural circuits mediating conditioned fear and innate fear,researches about conditioned fear and innate fear can only draw an incomplete picture of the brain's fear system,and cannot provide us a comprehensive understanding of neural mechanisms of fear.It is an important question about the understanding of fear that whether the same neural circuits mediate conditioned fear and innate fear.To investigate the above question,we firstly need to design a new behavioral paradigm,which uses the same or similar stimulus to elicit conditioned fear and innate fear respectively,and to trigger the same or similar behavioral responses.Before our research,some unpublished data in our laboratory revealed that not all looming stimulus in the overhead visual field could elicit innate defensive behavior in mice.Thus,in our research,we used the looming stimulus which could not elicit innate defensive behavior in mice as a conditioned stimulus paired with footshock,and established a new behavioral paradigm which could elicit conditioned fear in mice.We found that non-threatening looming stimulus could effectively elicit conditioned fear and flight behavior in mice.In behavioral tests,we found that the pairing of non-threatening looming stimulus and footshock had significant contribution to the production of conditioned fear in mice.This kind of conditioned fear could be learned within a relatively short time duration and a relatively few training times,and could maintain for a relatively long time duration.In addition,our experimental results revealed that the fear level of conditioned fear elicited by non-threatening looming stimulus in our new behavioral paradigm was no significant differences with that of innate fear elicited by threatening looming stimulus.We also simply investigated the neural mechanisms of conditioned fear elicited by non-threatening looming stimulus.We measured neuronal Ca²⁺signals in intermediate gray layer of superior colliculus and dorsomedial periaqueductal gray in mice using fiber photometry.We found that only non-threatening looming stimulus did not increase neuronal activities in these two brain regions before training.However,it could become a signal of threat and increased neuronal activities in these two brain regions after training.In addition,only threatening looming stimulus directly increased neuronal activities in these two brain regions.These results indicated that conditioned fear and innate fear elicited by looming stimulus might be mediated by similar neural mechanisms.Through our research,we hope we can provide our future research and other researchers with a new behavioral paradigm and a new research strategy about fear conditioning.We also hope we can provide people a deeper understanding of fear,and provide a research foundation of cure of diseases such as phobias,post-traumatic stress,anxiety disorders and so on.