Talya Sadeh and Jason Ozubko, Post Doctoral Fellows, Rotman Research Institute at
Jason Ozubko Title: Hippocampal Contributions to the Road Less Traveled: Using Google Street View to Examine Remote Spatial Memories in Virtualized Real-World Environments
Talya Sadeh Title: The Time of our Lives: Neural Mechanisms Supporting Temporal Organization of Episodic Memory
Ebbinghaus Empire Series 2013-2014 Jason Ozubko Talk Abstract:
The rise of virtual reality (VR) and neuroimaging technology in the past few decades has, for the first time, made it possible to study the neuropsychology of spatial memory during active navigation in humans. Studies using VR techniques have shown that the hippocampus plays an important role in the acquisition and short-term retention of spatial memories, however its long-term role is debated. Despite claims that the hippocampus is special in its role of representing spatial information, behavioural studies of remote spatial memory in patients with hippocampal lesions, and fMRI studies with healthy individuals using mental navigation, suggest that the hippocampus may not play a role in representing remotely learned spatial information. To directly address this issue, I developed a versatile VR paradigm that uses real-world panoramic, ground-level views, drawn from Google Street View. Using this technology, subjects were scanned in an fMRI while they navigated around a large scale city (Toronto, ON) along highly familiar, remotely acquired routes, as well as low familiarity routes, and “follow-the-arrow” control routes. Analyses revealed that the hippocampus was implicated in navigating along low familiarity routes but not highly familiar routes. Importantly, when the position of landmarks was mirror-reversed, the extra-hippocampal representations that support navigation in highly familiar environments were insufficient, and the hippocampus was recruited once again. Additionally, individuals who self-reported that they did not use mapping strategies while navigating were found to rely significantly less on their hippocampus during navigation. These results are discussed in a framework that emphasizes how the hippocampus may play an important role in dynamic, online map construction, rather than act as a storage site for mental maps per se. Talya Sadeh Talk Abstract:
When remembering previous events in our lives, the order in which we recall these events is not random, but rather follows a coherent, typically temporal, sequence corresponding to how the events unfolded over time. This reflects a core property of human memory: events are organized and retrieved in a coherent temporal sequence. In the current fMRI study we examined the mnemonic effects of temporal organization using free recall of word-lists. We capitalized on the temporal contiguity effect (TCE), which entails that the closer two words are during the study phase, the higher the probability that they will be retrieved in succession during the test phase. Hence, this effect captures the way in which retrieval of events from memory follows a temporal sequence. We found the TCE to be associated with activity in the anterior hippocampus. Furthermore, a functional-connectivity analysis with the hippocampus as a seed region revealed a set of regions which closely corresponds to that associated with retrieval of real-life, autobiographical memories, including midline structures involved in self-projection. Finally, across-subjects, the coherence between two primary midline regions, the medial prefrontal cortex and the posterior cingulate cortex, correlated with the magnitude of the TCE. Our results provide compelling evidence that the TCE relies on a similar neural circuitry to that of retrieval of real-life, autobiographical memories. We assert that this set of regions is guided by the hippocampus to support retrieval of events which are linked together by a coherent temporal order. Furthermore, recalling items according to temporal logic, as captured by the TCE, may reflect subjective organization of memories which strongly relies on self-projection.
For further information please contact Morgan Barense, barense @psych.utoronto.ca