Vicarious learning occurs when an “observer” animal, naïve to a conditioned stimulus, is in the presence of a “demonstrator” animal that has been conditioned to react to the stimulus. This project aimed to elucidate the mechanisms behind olfactory vicarious learning to an aversive cue; namely, how male rats observed and internalised the fear behaviour of other male rats.

A robust olfactory fear conditioning protocol was set up, in which an otherwise neutral odour, acetophenone, was paired with foot shocks. The rats subsequently displayed freezing behaviour. In order to assess the role of dominance in the home cages, dominance hierarchies were first measured through a resource competition task in which rats competed for an appetitive resource.

The conditioned demonstrator animals were placed with naïve observer animals and the conditioned odour was introduced for vicarious learning. All animals were then tested individually the next day, and freezing behaviour was measured. Observer rats successfully learned to freeze to the odour after the vicarious learning session with the demonstrator rat. To understand the mechanism behind fear transmission, pharmacological interventions and sensory modality manipulations were employed in different experiments. Rats learned to freeze to acetophenone through exposure to the odour in the presence of only a conditioned conspecific’s faeces and urine, which showed olfaction alone was sufficient for vicarious learning.

Oxytocin has previously been shown to modulate social behaviour as well as fear behaviour, and the release of oxytocin was shown to reduce freezing behaviour after direct and vicarious fear conditioning. However, injecting an oxytocin receptor antagonist to block oxytocin signaling prior to contextual conditioning did not have a significant effect on freezing behaviour. To investigate its effects on olfactory vicarious learning, an oxytocin receptor antagonist was injected into an observer animal prior to vicarious learning, and it did not show a significant effect on a rat’s ability to learn from its conspecific. On the other hand, the injection of an adrenergic receptor antagonist into an observer prior to vicarious learning did significantly block vicarious learning. Ultimately, isolating fear pheromones and targeting beta-adrenergic receptors in the observer had the greatest effect on a rat’s ability to learn to freeze to an odour vicariously.