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OFF-LINE REACTIVATION OF MEMORIES, DREAMS AND MEMORY CONSOLIDATION

Gaétane Deliens1*, Sophie Genin1, Sophie Galer1, 2 and Philippe Peigneux1, 2*
  • 1 Université Libre de Bruxelles, UR2NF, Neuropsychology and Functional Neuroimaging Research Unit, Université Libre de Bruxelles, Belgium
  • 2 LCFC, Laboratoire de Cartographie Fonctionnelle du Cerveau, Hôpital Erasme, Université Libre de Bruxelles, Belgium

It is now well established that sleep plays a promoting role in the off-line consolidation of newly learned memories (Peigneux & Smith, 2010). Several studies showed a positive correlation between elements incorporated in dreams and recall performance for these elements (Wamsley & Stickgold, 2011; Fiss et al., 1977; De Koninck et al., 1990; Cipolli et al., 2003, Cipolli et al., 2006). They concluded that incorporation of newly events into dream contents reflects an additional mnesic process during sleep, promoting memory consolidation (Nielsen et al., 2004).

To test this hypothesis, 30 subjects collected their dream experience during 12 nights. At day 8, a word-pairs and a 2D object-location memory tasks were administrated at 6 pm. In the word-pairs memory task, participants learned a list of 28 unrelated and emotionally neutral word pairs (75% learning criterion). The 2D object-location memory task was adapted from Wilhelm et al. (2008) and consisted of 15 card-pairs showing colored pictures of different animals and every-day objects. Subjects had to learn the location of the pairs presented on a grid. After presentation of the 15 pairs, immediate memory for the location of the second exemplar was tested by presenting the first element of each pair (60% learning criterion). The cued delayed recall phase of the two tasks was administered at day 12 at the same time than learning (6pm). For the word-pairs memory task, the first word of the pair (A) was presented and participants had to provide the associated word (B). Similarly, memory for object locations was tested by presenting the first picture of each pair and participants had to designate the location of the second same picture. Two naive judges independently identified potential incorporations of stimuli into dream contents from a given list. The list contained the 28 learned word pairs and the 15 learned cards mixed with 28 non-learned word pairs and the 15 non-learned cards using as distractors for judges.

Results revealed that the number of incorporation of learned words and pictures did not differ from incorporation of distractors (for word pairs p>.6; for pictures p>.3). Repeated measures ANOVA on the mean number of word pairs and pictures incorporated with factors Night (Nights 4 to 12) and Stimuli (Learned vs. Distractors) did not reveal any main Night (all p>.1) or Stimuli (all p>.1) nor interaction (all p>.5) effects. Percentage of word pairs and pictures incorporated into dream contents and correctly recalled did not differ from retention rate of stimuli not incorporated in dreams but correctly retrieved (p>.3 and p>.9 respectively).

In conclusion, these data did not confirm that off-line reactivation of recently learned memories into dream contents benefits retention. As the proportion of valid incorporations did not differ from pseudo-incorporation, we cannot either conclude that our learned stimuli were reactivated during sleep by incorporation intro dream contents after learning. One potential explanation would be that our stimuli are too common and consequently too similar to frequent reported dream contents rending their post-learned incorporation as frequent as pre-learned incorporation (false positive). Further studies are needed to replicate our experimental design with emotional or less frequent stimuli. Our study highlights the relevance of accounting pseudo-incorporation (dream incorporation during pre-learning nights) for investigating valid incorporations.

References

Cipolli, C., Fagioli, I., Mazetti, M., Tuozzi, G. (2006). Consolidation effect of repeated processing of declarative knowledge in mental experiences during human sleep. Brain research Bulletin, 69, 501-511.

Cipolli, C., Cicogna, PC., Mattarozzi, K., Mazzetti, M., Natale, V., Occhionero, M. (2003). Continuity of the processing of declarative knowledge during human sleep : evidence from interrelated contents of mental sleep experiences. Neuroscience Letters, 342, 147-150

De Koninck, J., Christ, G., Hebert, G., Rinfret, N. (1990). Language learning efficiency, dreams and REM sleep. Psychiatr J Univ Ottawa, 15, 91–92

Fiss, H., Kremer, E. and Litchman, J. (1977). The mnemonic function of dreaming. Sleep Research, 6, 122

Nielsen, T. A., Kuiken, D., Alain, G., Stenstrom, P., and Powell, R. (2004). Immediate and delayed incorporations of events into dreams: further replication and implications for dream function. Journal of Sleep Research, 13, 327-336.

Peigneux, P., and Smith, C. (2010). Memory Processing in Relation to Sleep. In : Meir H Kryger (Ed.), Principles and Practice of Sleep Medicine, 5th Edition. Philadelphia : Elsevier

Wamsley, E.J., and Stickgold, R. (2011). Memory, Sleep and Dreaming: Experiencing Consolidation. Sleep Med Clin, 6, 1, 97-108.

Wilhelm, I., Diekelmann, S., Born, J. (2008) Sleep in children improves memory performance on declarative but not procedural tasks. Learn Mem. 15, 5, 373-7

Keywords: Dreams, memory consolidation, stimulus incorporation, declarative memory, Sleep

Conference: Belgian Brain Council, Liège, Belgium, 27 Oct - 27 Oct, 2012.

Presentation Type: Poster Presentation

Topic: Higher Brain Functions in health and disease: cognition and memory

Citation: Deliens G, Genin S, Galer S and Peigneux P (2012). OFF-LINE REACTIVATION OF MEMORIES, DREAMS AND MEMORY CONSOLIDATION. Conference Abstract: Belgian Brain Council. doi: 10.3389/conf.fnhum.2012.210.00042

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Received: 04 Sep 2012; Published Online: 12 Sep 2012.

* Correspondence:
Miss. Gaétane Deliens, Université Libre de Bruxelles, UR2NF, Neuropsychology and Functional Neuroimaging Research Unit, Université Libre de Bruxelles, Brussels, Belgium, Gaetane.Deliens@ulb.ac.be
Prof. Philippe Peigneux, Université Libre de Bruxelles, UR2NF, Neuropsychology and Functional Neuroimaging Research Unit, Université Libre de Bruxelles, Brussels, Belgium, Philippe.Peigneux@ulb.ac.be