Noradrenergic arousal and systems consolidation: maintaining memory specificity?

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With time, memory is thought to undergo a neural reorganization, referred to as systems consolidation, during which memories are, at least partly, transferred from hippocampus to neocortical networks. This systems consolidation is highly dynamic and accompanied by a transformation from detailed, specific to more semantic, gist-like memory. Whether systems consolidation can be modulated is largely unknown. Emotional arousal-induced noradrenaline is known to be a powerful modulator of initial memory formation, leading via increased amygdala activity to increased memory strength and vividness as well as to enhanced hippocampal involvement in memory. Although it is well-established that noradrenaline may strengthen the initial consolidation of memory, its impact on systems consolidation processes and the time-dependent change in the specificity of memory is largely unknown. Based on recent rodent data, we hypothesize that post-encoding noradrenergic stimulation may change systems consolidation processes and maintain remote memories hippocampus dependent and specific. To test this hypothesis, healthy participants will be administered a placebo or the α2-adrenoceptor antagonist yohimbine, leading to increased noradrenergic stimulation, after they encode a series of neutral and emotionally arousing pictures. Memory will be tested in a recognition test, either 1 day or 28 days after encoding. To assess memory specificity, the recognition test will include, in addition to old and entirely novel items, lures carrying the gist of the initially encoded pictures as well as perceptually similar lures carrying a different gist. In order to assess the postulated systems consolidation and the neural underpinnings of post-encoding noradrenergic arousal on memory transformation, participants will be scanned with functional magnetic resonance imaging at 3T both during encoding and retention testing. Beyond their crucial relevance for our understanding of human memory in general and the long-term vividness of emotional memory in particular, the findings of this project might have implications for mental disorders in which aberrant emotional memory processing is prominent.