2025 Theses Doctoral

Understanding Memory Transformation through the Lens of Reactivation

Yu, Wangjing

Memories are not static records of our experiences. They are dynamic and undergo continuous change. Yet how memories transform awaits further characterization. This dissertation examines different forms of memory transformation through the lens of reactivation. Across three studies, I leverage the close link between memory transformation and reactivation to explore the transformation of repeated and once-encoded memories.

In chapter one, I focus on the process of ongoing memory consolidation, examining the offline reactivation dynamics of thrice- and once-encoded memories. I show that repeated learning leads to enhanced cortical reactivation and hippocampal-cortical coordinated reactivation during post-encoding rest periods, potentially accelerating systems-level consolidation.

Chapter two examines how successful retrieval of repeated memories is supported by reactivation in functionally distinct brain regions. This study demonstrates that the ventral temporal cortex preferentially reactivates the first occurrence of repeated events during active retrieval, but reactivation of the last occurrence in the left ventrolateral prefrontal cortex predicts memory accessibility.

Lastly, chapter three addresses the mechanistic role of memory reactivation in modulating the updating of repeated (strong) and once-encoded (weak) memories. I show that strongly encoded memories are more resistant to updating with new, conflicting information than weak memories. However, updating of a strong memory can be predicted by the degree of its reactivation at the time of new encoding. Further, weak memories, which are more flexible in incorporating new information compared to strong memories, exhibit overall heightened reactivation upon memory violation.

Together, these findings highlight that reactivation both reflects and modulates memory transformation, and that memory transformation and reactivation are adaptive to the repetitive yet ever-changing nature of our everyday experiences.