Encoding Fear

I found the second paper wholly impressive in its use of opto-genetics to inhibit the ACC->BLA circuit. The presentation of data was very complex in comparing the cue response neurons that changed frequency for the ACC and the BLA. I found it very interesting that they used a comprehensive pie chart to show whether the population of neurons that responded to a cue were excited or inhibited. It was interesting to note that a cue response will activate small proportion of neuronal ensemble in the ACC even when it is not paired with a fearful event. To me, this shows that the ACC encodes broad range of stimuli, and when fear is a component, it recruits a greater amount of excitatory neuronal ensemble. Lesions in the anterior-cingulate cortex have been noted to cause negative changes in mood and irritability. It is possible that a cue caused a small disturbance and thus a very small ensemble of excitatory neurons became recruited. Another interesting facet of the paper highlighted the fact that the BLA encoded the predictive value of a cue, and since its origin of projection was the ACC it is likely that this circuit plays a role in empathy. The BLA seems to encode fear based memories in a similar fashion to the hippocampus, in that it is not generalized but specific.

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