Abstract
Pairing a previously neutral conditioned stimulus (CS; e.g., a tone) to an aversive unconditioned stimulus (US; e.g., a foot-shock) leads to associative learning such that the tone alone will elicit a conditioned response (e.g., freezing). Individuals can also acquire fear from a social context, such as through observing the fear expression of a conspecific. In the current study, we examined the influence of kinship/familiarity on social transmission of fear in female rats. Rats were housed in triads with either sisters or non-related females. One rat from each cage was fear conditioned to a tone CS+ shock US. On day two, the conditioned rat was returned to the chamber accompanied by one of her cage mates. Both rats were allowed to behave freely, while the tone was played in the absence of the foot-shock. The previously untrained rat is referred to as the fear-conditioned by-proxy (FCbP) animal, as she would freeze based on observations of her cage-mate’s response rather than due to direct personal experience with the foot-shock. The third rat served as a cage-mate control. The third day, long-term memory tests to the CS were performed. Consistent with our previous application of this paradigm in male rats (Bruchey et al. in Behav Brain Res 214(1):80–84, 2010), our results revealed that social interactions between the fear conditioned and FCbP rats on day two contribute to freezing displayed by the FCbP rats on day three. In this experiment, prosocial behavior occurring at the termination of the cue on day two was significantly greater between sisters than their non-sister counterparts, and this behavior resulted in increased freezing on day three. Our results suggest that familiarity and/or kinship influences the social transmission of fear in female rats.
Highlights
Most animal models of fear learning focus on direct acquisition of fear, using variations of Pavlovian conditioning
We measured the duration of social interactions between the fear-conditioned by-proxy (FCbP) and fear-conditioned rat (FC rat) in the 20 s immediately following the termination of each conditioned stimulus (CS) during the fear-conditioning by-proxy session
There was a positive correlation between social interactions immediately post-cue and freezing displayed by the FCbP rat during long-term memory for both sister rats (r(17) = .83, p \ .001) and non-sister cage mates (r(15) = .67, p = .006) (Fig. 2b)
Summary
Most animal models of fear learning focus on direct acquisition of fear, using variations of Pavlovian conditioning Such experiments further our understanding of pathological fear and anxiety conditions seen in humans (including posttraumatic stress disorder and specific phobias); yet direct exposure to a stimulus is not the only way through which individuals acquire fear memories. Kavaliers et al (2005) demonstrated that deer mice acquire defensive behaviors to biting flies through observation, the efficacy of which depends on familiarity, kinship, and dominance. The importance of these social factors in Pavlovian-based fear conditioning is only just beginning to be investigated (Jeon et al 2010). In order to better understand social transmission of fear, the possible factors contributing to the social transmission need to be dissected
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