Sustained increase in hippocampal sharp-wave ripple activity during slow-wave sleep after learning.
High-frequency oscillations, known as sharp-wave/ripple (SPW-R) complexes occurring in hippocampus during slow-wave sleep (SWS), have been proposed to promote synaptic plasticity necessary for memory consolidation. We recorded sleep for 3 h after rats were trained on an odor-reward association task. Learning resulted in an increased number SPW-Rs during the first hour of post-learning SWS. The magnitude of ripple events and their duration were also elevated for up to 2 h after the newly formed memory. Rats that did not learn the discrimination during the training session did not show any change in SPW-Rs. Successful retrieval from remote memory was likewise accompanied by an increase in SPW-R density and magnitude, relative to the previously recorded baseline, but the effects were much shorter lasting and did not include increases in ripple duration and amplitude. A short-lasting increase of ripple activity was also observed when rats were rewarded for performing a motor component of the task only. There were no increases in ripple activity after habituation to the experimental environment. These experiments show that the characteristics of hippocampal high-frequency oscillations during SWS are affected by prior behavioral experience. Associative learning induces robust and sustained (up to 2 h) changes in several SPW-R characteristics, while after retrieval from remote memory or performance of a well-trained procedural aspect of the task, only transient changes in ripple density were induced.
Eschenko
Oxana
O
Neuromodulation, Neuroplasticity and Cognition, Centre National de la Recherche Scientifique (CNRS), UMR 7102, 75005 Paris, France.
Ramadan
Wiâm
W
Mölle
Matthias
M
Born
Jan
J
Sara
Susan J
SJ
D000818:Animals; D004569:Electroencephalography; D006624:Hippocampus / Q000502:physiology*; D007858:Learning / Q000502:physiology*; D051381:Rats; D012890:Sleep / Q000502:physiology*; D013997:Time Factors