Navigating memories: Space as an organizing principle in episodic memory

• Applicant: Dr. Nora Alicia Herweg
• Subject Area: General, Cognitive and Mathematical Psychology ; Human Cognitive and Systems Neuroscience
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 406909711

Space is one of the most fundamental dimensions along which we organize our perceptions and memories. Extensive research on the neurophysiology of spatial memory has been carried out in rodents in which invasive brain recordings can be obtained during navigation. Memory research in humans, in turn, has largely focused on more abstract language-based tasks that lack a spatial component. While studies in rodents have highlighted the role of place and grid cells in the medial temporal lobe (MTL) for spatial coding, studies in humans have implicated the MTL more generally in the formation and retrieval of episodic memories. To close the gap between these lines of research, I plan to use an established hybrid spatial-episodic memory task, in which participants navigate a virtual environment while encoding a set of objects and recall those objects later on. I am proposing to use a combination of computational modeling, electroencephalography (EEG) and intracranial electrophysiology in patients with pharmaco-resistant epilepsy to understand the spatial representation system in the human brain and its role in navigation and episodic memory. Intracranial data will be obtained from macro-electrodes used for seizure monitoring and from micro-wires extending from the tip of medial temporal depth electrodes to measure single unit activity (SUA) and local field potentials (LFPs). The data will be used to accomplish three aims: First, I will develop a computational model of human way finding to better understand the cognitive mechanisms involved in spatial memory and navigation. The model will describe how spatial information is encoded and retrieved to make navigational decisions, and will specifically distinguish navigation based on stimulus-response associations from more elaborate map-based navigation. Second, I will use EEG and intracranial recordings to characterize spatial representation with a focus on place-selective single cell responses, theta oscillations and their interaction (e.g. phase precession). For place-responsive cells, I will focus not only on local (i.e. spiking of place-responsive cells during periods in the virtual place field) but also on non-local (i.e. spiking of place-responsive cells during periods outside of the virtual place field) responses, which may play an important role in memory retrieval and decision making. Finally, I will characterize the neural basis of contextual retrieval in episodic recall and its role in organizing recall sequences. Here, I will focus on reinstatement of spatial information in sub-regions of the MTL and interconnected brain regions (e.g. in posterior parietal cortex). These multivariate analyses will be complemented by connectivity analyses to track the flow of information during recall.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Michael J. Kahana