PhD Scientific Days 2022

Neurosciences I. (Poster discussion will take place in the Aula during the Coffee Break)

Creating a False Fear Memory with Hippocampal Interneurons

Text of the abstract

Introduction: Neuronal assemblies in the hippocampus (HIPP) are large populations of neurons that are created by their own coordinated activity patterns. They can store different contextual memories. Fear memories are associated to the context coding assembly that is the most active during a fearful event. Understanding how previous memories and neuronal activities influence the selection of these assemblies are essential for understanding the creation of true and false fear memories. Our recent findings revealed that the activity pattern of HIPP somatostatin (SOM) positive interneurons or their brainstem inputs could control HIPP memory acquisition and recall efficiently.

Aims: Here, we investigated the long-term plasticity of neuronal assemblies. We tested whether pre-activation of a neuronal assembly a day before a fearful contextual event can prepare it to store the fearful contextual event a day later with higher probability. We also hypothesized that the activity pattern of HIPP SOM interneurons is crucial in these associations leading to its role in false fear memory association.

Method: We used optogenetic behavioral experiments, viral track tracing and neuroanatomical methods in transgenic animals that allowed us to investigate these questions in a brain region in a cell type specific manner.

Results: Using optogenetic inhibition of a subpopulation of HIPP SOM interneurons (either directly or indirectly by activating their brainstem inhibitory inputs), we selectively activated a HIPP neuronal assembly in a neutral environment. Then, we found that this assembly had preferentially encoded a fear memory a day later. We observed that mice showed fear memory in a context specific manner even in an environment, where they had never experienced fear.

Conclusion: Our preliminary findings suggest that manipulation of HIPP interneurons or their brainstem inputs can induce false associations. Understanding this kind of mechanism would be important in finding treatment in many types of anxiety-related mental conditions.

Funding: This project was supported by the ÚNKP-21-3-I-SE-9 New National Excellence Program of the Ministry of Innovation and by the EFOP-3.6.3-VEKOP-16-2017-00009 Semmelweis 250+ Excellence PhD Fellowship.