Noradrenergic arousal and systems consolidation: maintaining memory specificity?
Human Cognitive and Systems Neuroscience
Final Report Abstract
Memories evolve over time. Specifically, memories are thought to undergo a neural reorganization over time, referred to as systems consolidation, during which memories become less dependent on the hippocampus and more reliant on neocortical areas. This systems consolidation is further assumed to be accompanied by a transformation from detailed memories to more gist-like representations. The present project asked whether the fundamental process of systems consolidation can be experimentally manipulated. Based on recent data in rodents, we hypothesized that noradrenergic stimulation shortly after encoding can reverse the course of systems consolidation. In addition, we aimed to further characterize the nature of the proposed transformation of memories over time, testing whether this transformation is primarily semantic or perceptual in nature. To this end, healthy participants were administered a placebo or the α2-adrenoceptor antagonist yohimbine, leading to increased noradrenergic stimulation, shortly before they encoded a series of images. Memory for these images was tested in a recognition test either 1d or 28d later, thus allowing us to probe timedependent changes in memory. The recognition test included, in addition to old and entirely new images, images that were semantically or perceptually related to the encoded images, which enabled us to assess qualitative changes in memory. Importantly, both encoding and recognition testing took place in an MRI scanner. Our results showed that yohimbine reduced the time-dependent decline in memory over time. Even more interestingly, yohimbine appeared to reverse the course of systems consolidation, leading to even increased hippocampal and reduced neocortical involvement in memory over time. This noradrenaline-induced reversal of systems consolidation might be a key mechanism to keep memories for emotionally arousing events vivid in the long run. Moreover, our data revealed that the time-dependent transformation of memory is semantical but not perceptual in nature and linked to distinct time-dependent changes of mnemonic representations along the hippocampal long axis as well as in neocortical areas. This semantic transformation may promote the integration of memories into more abstract knowledge structures. Together, these results provide novel insights into the dynamics and nature of a fundamental aspect of memory, its evolution over time. Beyond their relevance for our understanding of human memory, the present findings might have relevant implications for mental disorders characterized by aberrant memory for emotionallyarousing events.
Publications
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Noradrenergic arousal after encoding reverses the course of systems consolidation in humans. Nature Communications, 12(1).
Krenz, Valentina; Sommer, Tobias; Alink, Arjen; Roozendaal, Benno & Schwabe, Lars
