Retrieval dynamics in episodic memory – from computations to representations

Understanding how our experiences are retrieved from long-term memory is fundamental in cognitive neuroscience. In this doctoral thesis I explore two essential questions regarding the temporal dynamics of episodic memory retrieval. First, I investigate how rapidly distinct components of a visual object representation (i.e., perceptual and conceptual aspects) are reactivated during retrieval, and how this temporal sequence evolves compared to visual encoding. Findings from a series of behavioural, scalp electroencephalography (EEG) and intracranial EEG experiments, using reaction times and time- resolved decoding analyses, suggest that retrieval is a hierarchical, multi- layered process that follows the reverse order compared to encoding, prioritizing semantic information over perceptual details. Second, I explore whether memories are reactivated following a specific oscillatory rhythm. Computational models, based on studies in rodents, suggest that encoding and retrieval processes occur at opposing phases of hippocampal theta oscillations. Evidence for such phase modulation in humans is still sparse. The present findings suggest that in humans, neural signatures of memory retrieval fluctuate with, and are time-locked to, the phase of theta oscillations. Altogether, this doctoral thesis supports the view that retrieval is an oscillatory process and the elements that form our memories are retrieved following a biased and sequential order