Sleep stage II contributes to the consolidation of declarative memories

Various studies suggest that non-rapid eye movement (NREM) sleep, especially slow-wave sleep (SWS), is vital to the consolidation of declarative memories. However, sleep stage 2 (S2), which is the other NREM sleep stage besides SWS, has gained only little attention. The current study investigated whether S2 during an afternoon nap contributes to the consolidation of declarative memories. Participants learned associations between faces and cities prior to a brief nap. A cued recall test was administered before and following the nap. Spindle, delta and slow oscillation activity was recorded during S2 in the nap following learning and in a control nap. Increases in spindle activity, delta activity, and slow oscillation activity in S2 in the nap following learning compared to the control nap were associated with enhanced retention of face-city associations. Furthermore, spindles tended to occur more frequently during up-states than down-states within slow oscillations during S2 following learning versus S2 of the control nap. These findings suggest that spindles, delta waves, and slow oscillations might promote memory consolidation not only during SWS, as shown earlier, but also during S2.

Offline consolidation in implicit sequence learning

The goal of this study was to investigate offline memory consolidation with regard to general motor skill learning and implicit sequence-specific learning. We trained young adults on a serial reaction time task with a retention interval of either 24 hours (Experiment 1) or 1 week (Experiment 2) between two sessions. We manipulated sequence complexity (deterministic vs. probabilistic) and motor responses (unimanual or vs. bimanual). We found no evidence of offline memory consolidation for sequencespecific learning with either interval (in the sense of no deterioration over the interval but no further improvement either). However, we did find evidence of offline enhancement of general motor skill learning with both intervals, independent of kind of sequence or kind of response. These results suggest that general motor skill learning, but not sequence-specific learning, appears to be enhanced during offline intervals in implicit sequence learning.

Habituation and consolidation of prospective memory over a week: An ERP study

Prospective memory (ProM) is the ability to remember and perform an intention in the future. If a prospective memory task is to be performed only once, it is episodic. If it is repeated, then it becomes habitual. Thus, with repetition, a task changes from episodic to habitual. The goal of this study was to investigate the transition from episodic to habitual prospective memory with event-related potentials (ERP). The ProM task was to respond to a target word which was embedded in an ongoing lexical decision task. 40 ProM trials were administered in each of two sessions that were separated by a week. The results revealed a behavioural consolidation effect with increased ProM performance after one week. The ERP-analyses showed that when the task became more habitual a difference occurred in a time-window between 450-650 ms post-stimulus in an ERP-component. In addition, a covariance analysis revealed that this transition is continued in the second session. These results demonstrate that the transition from episodic to habitual prospective memory is long-lasting and continuous.

Prestimulus default mode activity influences depth of processing and recognition in an emotional memory task

Low self-referential thoughts are associated with better concentration, which leads to deeper encoding and increases learning and subsequent retrieval. There is evidence that being engaged in externally rather than internally focused tasks is related to low neural activity in the default mode network (DMN) promoting open mind and the deep elaboration of new information. Thus, reduced DMN activity should lead to enhanced concentration, comprehensive stimulus evaluation including emotional categorization, deeper stimulus processing, and better long-term retention over one whole week. In this fMRI study, we investigated brain activation preceding and during incidental encoding of emotional pictures and on subsequent recognition performance. During fMRI, 24 subjects were exposed to 80 pictures of different emotional valence and subsequently asked to complete an online recognition task one week later. Results indicate that neural activity within the medial temporal lobes during encoding predicts subsequent memory performance. Moreover, a low activity of the default mode network preceding incidental encoding leads to slightly better recognition performance independent of the emotional perception of a picture. The findings indicate that the suppression of internally-oriented thoughts leads to a more comprehensive and thorough evaluation of a stimulus and its emotional valence. Reduced activation of the DMN prior to stimulus onset is associated with deeper encoding and enhanced consolidation and retrieval performance even one week later. Even small prestimulus lapses of attention influence consolidation and subsequent recognition performance. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc.