A dedicated cortico-hippocampal network changes the behavioral output of learning ensembles in the striatum

Fear learning relies on widely distributed networks of neuronal ensembles. These ensembles represent a fundamental mechanism through which the brain processes and organizes information, creating patterns of neural activity associated with different aspects of memory.
Projections from many brain areas involved in fear are known to converge onto the dorsomedial part of the striatum (DMS), which plays an essential role in the extinction of fear memories. However, it is still unknown whether learning ensembles are formed within this inhibitory neural circuit and, if so, what their functional role is in supporting learning and updating.
In this thesis, I provide evidence that a memory ensemble is formed in the DMS as a consequence of fear learning. Using the immediate early gene cFos as a marker of neuronal activity, I show a novel, functional role for this striatal ensemble during behavioral flexibility and characterize how its final output is orchestrated through the various phases of learning.
By combinatorial interfering with neuronal activity in the individual network nodes, I show that a dedicated cortico-hippocampal network involving the dorsal hippocampus (dHp) and the retrosplenial cortex (RSC) is specifically recruited during extinction to influence the activity of the DMS fear ensemble.