The competition of semantic information and episodic experiences and its modulation by stress
The scenario construction model states that episodic recall is a generative process, which supplements a “gist” retrieved from episodic memory with information from semantic memory. A key prediction is that memory retrieval is biased toward semantically congruent information. The central aim of P4 is to test this hypothesis experimentally and to investigate the neural signature of scenario construction. A core component of each episodic memory is its unique spatio-temporal context. In the first funding period, we used a novel virtual apartment task to show that existing semantic associations between objects and locations bias participants’ memory for spatial context. Going forward, we will continue this line of research while adding a thorough assessment of semantic effects on memory for temporal context. We designed two behavioral paradigms that allow us to assess participants’ memory for the temporal order of semantically structured sequences with (1) high experimental control and (2) high external validity, respectively. We predict that, like in the spatial domain, participants use semantic information to reconstruct temporal sequences and thereby compensate for weak episodic memory traces (Objective 1). Using fMRI, EEG and multivariate analyses, we aim to study hippocampal representations and theta oscillations at encoding and retrieval. We will test the idea that semantic representations in the hippocampus along with theta oscillations support the construction of extended temporal sequences (Objective 2). Finally, we will continue to characterize the modulatory role of stress in scenario construction. Using cortisol administrations as well as a social stress intervention prior to encoding, retrieval, or both, we aim to show that stress reduces the contribution of episodic memory traces during scenario construction and thereby enhances semantic construction effects (Objective 3). In summary, this project will assess semantic construction effects at the level of participants’ behavior, characterize the underlying representations in the hippocampal network, and probe its modulation by stress. As such, our results will guide the specification of the scenario construction model.
Where was the toaster? A systematic investigation of semantic construction in a new virtual episodic memory paradigm