Celebration of Learning

Impact of Social Contact on Predator-Induced Fear Responses in Young Male Chicks

Post-Traumatic Stress Disorder (PTSD) is thought to involve unusually strong associative memories between the intense fear felt during a traumatic experience and other environmental cues present at the time of the trauma. Our study uses an animal model to investigate social contact, one of the factors that can impact fear responses, to learn more about possible risk factors or interventions that may be relevant to humans who may experience PTSD. Freezing, or the cessation of movement, is a common fear response observed in laboratory animals in the presence of a perceived threat. We tested whether or not the degree of fear expressed by a social companion impacted the level of fear demonstrated by young male chicks. We initially predicted that the presence of a companion would reduce the fear demonstrated by a chick in response to an audiovisual predator stimulus, known as social buffering of fear. Previous results in our lab actually demonstrated the opposite effect. Chicks that experienced predator stimuli in the presence of another chick remained immobile longer than those who experienced the predator alone. It seemed as though chicks were mirroring the fear expressed by their companion. The current study was aimed at investigating whether social transmission of fear is, in fact, occurring between chicks. In order to more carefully control the fear response of companion chicks, we created two different videos to serve as the “companion” stimuli in this experiment. In one, a control chick walked around naturally, and in another, the chick demonstrated fear that was timed to the onset of the predator stimulus. After three daily habituation sessions to the testing apparatus and video screen, 48 Cornish Cross chicks were exposed to one of four conditions: no predator stimulus and a non-fearful video companion, no predator stimulus and a fearful companion, predator stimulus and a non-fearful companion, or predator stimulus and a fearful companion. One chick from each home cage was randomly assigned to each condition. Half of the chicks were exposed to the predator stimuli and half were not. In each group, half were paired with a fearful companion video and half were paired with a non-fearful companion video. Activity of each chick was recorded and quantified by behavioral analysis software (Smart 3.0, Panlab). Statistical analysis revealed a significant main effect of the predator stimulus, F(1, 89) = 28.11, p