ACC-BLA Connections and Observational Learning- Annissa DeSilva



           
Observational fear learning is an innate social behavior, Allsop et al. 2018 outlines the neural circuit underlying how the brain encodes emotionally salient (fear) behavior with neutral cues associated through observational fear learning. Allsop et al, found that projections from the Anterior cingulate cortex (ACC) to the Basolateral Amygdala (BLA) are essential in encoding observational learning. Specifically observing distress causes basal changes in the ACC neurons (encoding of the observed behavior through social cues) which enables the acquisition of the predictive nature of the aversive cue by BLA neurons. When ACC-BLA projections were optogenetically inhibited while mice were observing fear conditioning a reduced freezing response was seen when conditioned fear response was tested. Interestingly when the ACC-BLA projections were inhibited during testing of observational fear conditioning there was no effect on freezing. The researchers suggest that ACC-BLA projections may be exclusively related to social cue acquisition not fear expression. This is interesting especially in the framework of mental illnesses related to abnormal social functioning or reaction social cues such autism. I think this research is groundbreaking because understanding how a neural circuit functions is an essential first step in understanding which processes underlie and produce specific behaviors. In many of my previous classes there is an emphasis that mental illness results from dysfunction at circuit level so understanding the ACC-BLA circuit opens up possibility to investigate how alterations and dysfunction in this circuit may lead to abnormal fear acquisition and thus social behavior through observational learning. Perhaps increased sensitivity in the ACC may cause the BLA to form abnormal or stronger associations to be formed to inappropriate stimuli even when observed, causing behavioral deficits.
            Paired with the Sial et al. 2015 it was interesting to see the justification for use of observational fear conditioning and vicarious social defeat paradigm (VSD). This paradigm and the notion of using of emotional stressors to induce depression/anxiety like behavior versus physical stressors seems much more etiologically valid especially considering that the paradigm produces similar behavioral deficits and the effects are seen up to a month after exposure. I think it would be interesting to see studies that examine antidepressant and Anxiolytic action to use this paradigm compared with traditional means of inducing depression in mice (ex.CMS) to see if drug action efficacy varies as a function of source of stressor, or if the same functional changes due to CMS seen in  depressed mice is mirrored in mice who underwent VSD.

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