Emotional Stress and Observational Learning


Sial et al., 2015 introduced the vicarious defeat stress model (VSDS) to help separate the influence of physical stressors from emotional stressors. Instead of measuring the effects of social defeat on mice, the VSDS measures the effects of observing other mice experiencing social defeat. This includes a witness component and theoretically helps separate psychological stress from physical stress in mice. Both emotional and physical stress decrease weight gain, more so with emotional stress. However, these measures returned to baseline within a couple days. Mice were then tested with the social interaction test and elevated plus-maze. Both PS and ES resulted in social avoidance and reduced time in the open arms of the maze. Fluoxetine injections reversed induced phenotypes in both groups over 30 days, not after a single injection.
Allsop et al., 2018 used several experimental groups to study observational learning in mice and how it relates to the BLA and ACC. They wanted to answer questions regarding the function of the ACC-BLA pathway and the directionality of information. In the standard experimental group, mice were administered a single foot shock, then watched a demonstrator receive 30 foot shocks. The other groups controlled for shock experience, paired cue and shock, and/or the presence of a demonstrator, for a total of five groups. Mice that witnessed another mouse be shocked by a paired cue and shock (both the EO and NO groups) showed increased freezing when given the cue the next day. The EO group showed place avoidance, but not freezing behavior. Next, using single-unit recordings, they found that the predictive value of the cue regulates whether it was encoded by the BLA, while the ACC reflected predictive value through response magnitude. ACC neurons were found to demonstrate an association between cue and shock earlier than the BLA, then transmit the information to the BLA, which fully forms the association. Partially inhibiting this pathway showed this information exchange is necessary for observational learning, and the activity is greatest during the cue. Finally, the ACC-BLA pathway is important in avoidance following observation of social defeat.
I am skeptical about the ability of a mouse to distinguish between physical and emotional stress, at least to the extent of being able to use it as a model for stress-related disorders in humans. Mice have much simpler brains than humans and are clearly unable to experience our range of emotions. Observational learning is an evolutionary advantage for any animal, as it helps them stay out of trouble. It’s easy for me to believe that mice observed another mouse being distressed in a certain context, then learned to stay away from that situation. However, I find it hard to believe that the mere experience of seeing another mouse in danger caused them emotional stress. Nonetheless, the article claimed that VSDS induces social avoidance, so I’d like to look further into this area of research and see what other labs think about the emotional capacity of mice and just how applicable their stress is to PTSD.
Regarding Sial et al.’s article, it would be interesting for further research to investigate any other effects observational learning has on mice, such as whether its severity can lead to stress in the witness mouse. If the claims from Sial et al. are accurate and there is a distinct difference between physical and emotional stress in mice, I am wondering if it is possible for Allsop’s paper to also be tapping into emotional stress, not just observational learning. The mice could be responding to the stress of witnessing another stressed mouse, as well as learning about the context of said stress.

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