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The Journal of Neuroscience, December 13, 2006, 26(50):12914-12920; doi:10.1523/JNEUROSCI.3175-06.2006

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Behavioral/Systems/Cognitive
Elevated Sleep Spindle Density after Learning or after Retrieval in Rats

Oxana Eschenko,¹ Matthias Mölle,² Jan Born,² and Susan J. Sara¹

¹Department of Neuromodulation, Neuroplasticity, and Cognition, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7102, Université Paris 6, 75005 Paris, France, and ²Department of Neuroendocrinology, University of Lübeck, 23538 Lübeck, Germany

Correspondence should be addressed to Dr. Susan J. Sara, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7152, College de France, 75005 Paris, France. Email: sjsara{at}ccr.jussieu.fr

Non-rapid eye movement sleep has been strongly implicated in consolidation of both declarative and procedural memory in humans. Elevated sleep-spindle density in slow-wave sleep after learning has been shown recently in humans. It has been proposed that sleep spindles, 12–15 Hz oscillations superimposed on slow waves (<1 Hz), in concert with high-frequency hippocampal sharp waves/ripples, promote neural plasticity underlying remote memory formation. The present study reports the first indication of learning-associated increase in spindle density in the rat, providing an animal model to study the role of brain oscillations in memory consolidation during sleep. An odor–reward association task, analogous in many respects to human paired-associate learning, is rapidly learned and leads to robust memory in rats. Rats learned the task over 10 massed trials within a single session, and EEG was monitored for 3 h after learning. Learning-induced increase in spindle density is reliably reproduced in rats in two different learning situations, differing primarily in the behavioral component of the task. This increase in spindle density is also present after reactivation of remote memory and in situations when memory update is required; it is not observed after noncontingent exposure to reward and training context. The latter results substantially extend findings in humans. The magnitude of increase (25%) and the time window of maximal effect (1 h after sleep onset) were remarkably similar to human data, making this a valid rodent model to study network interactions through the use of simultaneous unit recordings and local field potentials during postlearning sleep.

Key words: spindles; slow-wave sleep; memory consolidation; retrieval; off-line processing; rats

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Received July 25, 2006; revised Oct. 25, 2006; accepted Oct. 26, 2006.

Correspondence should be addressed to Dr. Susan J. Sara, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7152, College de France, 75005 Paris, France. Email: sjsara{at}ccr.jussieu.fr

This article has been cited by other articles:

				O. Eschenko, W. Ramadan, M. Molle, J. Born, and S. J. Sara Sustained increase in hippocampal sharp-wave ripple activity during slow-wave sleep after learning Learn. Mem., April 2, 2008; 15(4): 222 - 228. [Abstract] [Full Text] [PDF]

				O. Eschenko and S. J. Sara Learning-Dependent, Transient Increase of Activity in Noradrenergic Neurons of Locus Coeruleus during Slow Wave Sleep in the Rat: Brain Stem-Cortex Interplay for Memory Consolidation? Cereb Cortex, March 4, 2008; (2008) bhn020v1. [Abstract] [Full Text] [PDF]

				K. L. Hoffman, F. P. Battaglia, K. Harris, J. N. MacLean, L. Marshall, and M. R. Mehta The Upshot of Up States in the Neocortex: From Slow Oscillations to Memory Formation J. Neurosci., October 31, 2007; 27(44): 11838 - 11841. [Full Text] [PDF]

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