Increased Resting-State Perfusion after Repeated Encoding Is Related to Later Retrieval of Declarative Associative Memories

Abstract

Electrophysiological studies in animals have shown coordinated reactivation of neuronal ensembles during a restricted time period of behavioral inactivity that immediately followed active encoding. In the present study we directly investigated off-line processing of associative memory formation in the human brain. Subjects' regional cerebral blood flow (rCBF) as a surrogate marker of neural activity during rest was measured by MR-based perfusion imaging in a sample of 14 healthy male subjects prior to (Pre2) and after (Post) extensive learning of 24 face-name associations within a selective reminding task (SR). Results demonstrated significant Post-Pre2 rCBF increases in hippocampal and temporal lobe regions, while in a control comparison of two perfusion scans with no learning task in-between (Pre2-Pre1) no differences in rCBF emerged. Post perfusion scanning was followed by a surprise cued associative recall task from which two types of correctly retrieved names were obtained: older names already correctly retrieved at least once during one of the SR blocks, and recent names acquired during the last SR block immediately prior to the Post scan. In the anterior hippocampus individual perfusion increases were correlated with both correct retrievals of older and recent names. By contrast, older but not recently learned names showed a significant correlation with perfusion increases in the left lateral temporal cortex known to be associated with long-term memory. Recent, but not older names were correlated with dopaminergic midbrain structures reported to contribute to the persistence of memory traces for novel information. Although the direct investigation of off-line memory processing did not permit concomitant experimental control, neither intentional rehearsal, nor substantial variations in subjects' states of alertness appear to contribute to present results. We suggest that the observed rCBF increases might reflect processes that possibly contribute to the long-term persistence of memory traces.

Persistence of hippocampal multivoxel patterns into postencoding rest is related to memory

“…Specifically, it has been hypothesized that time periods that engender a reduction in environmental stimulation may allow for the expression of physiological mechanisms underlying memory consolidation (3,40). Additionally, robust and reliable patterns of connectivity are known to occur during awake rest (41,42), and several recent studies have shown that overall univariate measures of blood flow, BOLD responses, and BOLD connectivity during awake rest may be modulated in a manner consistent with memory consolidation (21)(22)(23)(24)(25). Here, we extend these results by showing that multivariate encoding-related hippocampal BOLD patterns persist into awake rest periods and that this persistence is related to future overall memory for prerest experiences.…”

“…Critical for theories of consolidation, the extent of hippocampal reactivation in rodents has recently been related to spatial memory improvements (17), whereas interference with putative reactivation events leads to impairments in learning (18)(19)(20). Prior work in humans using functional MRI (fMRI) has shown that resting connectivity between the hippocampus and encoding-related cortical areas can be modulated by an associative encoding experience (21,22) and that these experience-related changes are correlated with later memory (21,23). Additionally, overall changes in activity and connectivity in the hippocampus and cortical regions have been shown to occur during slowwave sleep and subsequent task performance (24,25).…”

The effect of age on relational encoding as revealed by hippocampal functional connectivity

“…Third, resting state data was acquired after the memory task. The ordering of these tasks has been shown to have an impact on connectivity of the DMN (Groen et al, 2011). We adopted this methodology as a strategy to reduce the time between training and performance on the task.…”

“…The goal of this design was to reduce the delay between instruction and practice for the task and engagement in the in-scanner task. Although Groen, Sokolov, Jonas, Roebling, & Spitzer (2011) showed evidence that post-learning resting state data can be influenced by the preceding cognitive task, Grady et al (2010) were able to extract the core components of the DMN even during fixations that were interspersed between tasks. This suggests that the key components of the DMN are robust even when collected after a task has been administered.…”

"Nuclear" medicine physicians as communicators: their point of view on the aftermath of "nuclear" disaster

“…In conclusion, transport information like warnings and how to behave in disasters (evacuation, sheltering, iodine blockade and food ban) to the public in a way that it will be perceived, keep it simple, straight forward and repeat it to gain statistical significant levels for brain memory cells in the hippocampus [36].…”