Investigation of the boundary conditions and the function of the ventral hippocampus for well-learned instrumental memory reconsolidation

Cheng, Chaoran (2023). Investigation of the boundary conditions and the function of the ventral hippocampus for well-learned instrumental memory reconsolidation. University of Birmingham. Ph.D.

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Abstract

Well-learned instrumental memory was thought both to be robust and unable to undergo reconsolidation. However, the current study showed that a certain contingency change was required to overcome the prediction error signal threshold in order to trigger a well-learned memory reconsolidation. In this study, we investigated different experimental models to study well-learned memory reconsolidation, which neural circuit may be involved and the boundary conditions of well-learned instrumental memory reconsolidation. We found with a mild contingency change (VR5) the two-lever model is the most suitable model to study well-learned memory reconsolidation and the delayed reactivation method which reactivated 48 hours (a gap day) after training to be the most consistent reactivation parameter to destabilise the memory. This may be ascribed to the gap day facilitating memory destabilization. But any procedures except memantine injection, even handling, during the gap day may prevent the facilitation effect and animals do not show signs of instrumental memory destabilization in the following test session. Furthermore, our data also suggest the ventral hippocampus may be required to trigger instrumental memory destabilization. Despite a lack of statistical power, our immunohistochemistry data of zif268 expression suggests that the infralimbic region and prelimbic region may be involved in instrumental memory reconsolidation. However, further studies are required for confirmation. Overall, this study demonstrates a new protocol that can consistently destabilise the well-learned instrumental memory which can be used for further instrumental memory studies and showed the ventral hippocampus is required for well-learned instrumental memory destabilisation.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):