Abstract
In humans, exposure to novel images and exploration of novel virtual environments before the encoding of words improved subsequent memory performance. Animal studies revealed similar effects of novelty, both before and after learning, and could show that hippocampus-dependent dopaminergic neuromodulation plays an important role. Here, we further investigated the effects of novelty on long-term memory in humans using a novel paradigm employing short sequences of nature movies presented either before or at two time points after learning of unrelated words. Since novelty processing is associated with a release of dopamine into the hippocampus, we hypothesized that novelty exposure primarily affects hippocampus-dependent memory (i.e., recollection) but not hippocampus-independent memory (i.e., familiarity). We tested 182 healthy human subjects in three experiments including a word-learning task followed by a 1-day delayed recognition task. Importantly, participants were exposed to novel (NOV) or familiar movies (FAM) at three time points: (experiment 1) directly after encoding of the word list, (experiment 2) 15 min after encoding, (experiment 3) 15 min prior to encoding. As expected, novel movies were perceived as more interesting and led to better mood. During word recognition, reaction times were faster for remember as compared to familiarity responses in all three experiments, but this effect was not modulated by novelty. In contrast to our main hypothesis, there was no effect of novelty – before or after encoding – on subsequent word recognition, including recollection and familiarity scores. Therefore, an exposure to novel movies without an active task does not affect hippocampus-dependent and hippocampus-independent long-term recognition memory for words in humans.
Highlights
A few recent studies in humans have shown that the exposure to novelty before a learning phase improves subsequent memory (Fenker et al, 2008; Ballarini et al, 2013; Schomaker et al, 2014)
No significant main effects or interactions could be observed for corrected hit rates (cHRs)-remember [time point: F(2,176) = 0.990, p = 0.374, partial η2 = 0.011; novelty: F(1,176) = 0.790, p = 0.375, partial η2 = 0.004; novelty × time point: F(2,176) = 0.092, p = 0.912, partial η2 = 0.001]
We investigated whether the exposure to novel nature movies before or after encoding of a word list can improve subsequent long-term memory performance
Summary
A few recent studies in humans have shown that the exposure to novelty before a learning phase improves subsequent memory (Fenker et al, 2008; Ballarini et al, 2013; Schomaker et al, 2014). Novelty Does Not Improve Recognition with very familiar images (Bunzeck and Düzel, 2006) These observations in humans largely fit to animal studies, which show that long-term memory is promoted through novelty exploration before – and after – learning (Moncada and Viola, 2007; Wang et al, 2010). The late phase of hippocampal long-term potentiation (LTP) is DA dependent (O’Carroll and Morris, 2004; Granado et al, 2008), and injections of DA agonists into the hippocampus improve memory processes in rats (Packard and White, 1991). The role of the SN/VTA, hippocampus and DA in novelty processing has been underlined in functional imaging studies in humans (Chowdhury et al, 2012; Bunzeck et al, 2014), and the hippocampal-VTA model helps to explain the beneficial effects of novelty on long-term memory. More direct evidence comes from Wang et al who could show in rats that novelty exploration after spatial encoding improves long-term place-memory (i.e., at a behavioral level), and this effect was blocked by D1/D5 receptor antagonists (Wang et al, 2010)
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