The project has developed a new paradigm for testing episodic memories with fMRI, which has produced very exciting results. The paradigm is adapted so it can be used to study encoding, consolidation, and retrieval of episodic memories, and can also be used in combination with targeted memory reactivation paradigms during polysomnography or sleep-fMRI.
We have also used major efforts to develop, adapt and implement a processing pipeline for multi-modal neuroimaging. This is customized to the project, allows us to run integrated analyses across may different brain imaging techniques that are used for different purposes is the project. This includes task- and resting state fMRI, structural, diffusion tensor imaging (DTI), positron emission tomography (PET) and electrophysiological (EEG) data, which is a critical part of the project. Following recent standards for reproducible neuroimaging, the organization of MRI, PET and EEG-data collected in the project adheres to the Brain Imaging Data Structure specifications (BIDS -
https://bids.neuroimaging.io(opens in new window)).
Scientifically, the project has so far contributed with several publications in scientific journals, as well as a number of talks and presentations on conferences, meetings, seminars and workshops. Of the results so far, the followings can be highlighted:
Of the most important, we have shown that sleep patterns are related to accumulation of the Alzheimer’s Disease biomarker beta-amyloid, and this relationship is especially strong in regions with high expression of the HOMER1 gene (Fjell et al., 2020, Cerebral Cortex). HOMER1 is involved both in regulation of the sleep-wake cycle, as well as in processing of beta-amyloid. We also detected a relationship between more sleep problems and worsening of long-term memory, suggesting a link between sleep, beta-amyloid, gene expression and long-term memory in aging. We further found that aspects of sleep were related to changes in microstructural integrity in the hippocampus (Grydeland et al., 2021, Sleep).
In another manuscripts (Fjell et al. 2020 Sleep), we took these analyses further, showing an age-dependent relationship between sleep and brain atrophy in regions known to be heavily involved in consolidation of episodic memories, as well as age-invariant relationships to restricted cortical regions (Fjell et al., 2021, Cerebral Cortex).
Together, the results of these manuscripts add substantially to our knowledge about memory consolidation deficits in aging, sleep and brain atrophy.
Other papers have focused on the role of encoding strategies for consolidation of long-term memories (Amlien et al., Scientific reports, 2019), and on the differential roles played by anterior and posterior parts of the hippocampus (Langnes et al., Hippocampus 2020) in long-term episodic memory encoding and retrieval.
An exciting line of analyses focused on functional connectivity during different memory task states, e.g. how different brain regions communicate during cognitive activity, and whether this has bearings on age-differences in memory consolidation. In one manuscript, we found support a theory of striatal alterations as one cause of cognitive decline in aging and highlighted that age-related changes in episodic memory extend beyond hippocampal-neocortical connections (Ness et al., Cerebral Cortex). Further, we found increased post-encoding functional connectivity between hippocampus and individually localized neocortical regions responsive to stimuli encountered during memory encoding (Folvik et al., 2023, Cerebral Cortex). Post-encoding modulations were manifested as a nearly system-wide upregulation in hippocampal coupling with all major functional networks. The configuration of these extensive modulations resembled hippocampal-neocortical interaction patterns estimated from active encoding operations, suggesting hippocampal post-encoding involvement exceeds perceptual aspects. We concluded that the similarity in hippocampal functional coupling between online memory encoding and offline post-encoding rest suggests that reactivation in humans involves a spectrum of cognitive processes engaged during the experience of an event. In two recent papers we also tested memory-related connectivity during different task states (Raud et al., 2023, Neuroimage; Capogna et al., Cerebral Cortex).
