Transcranial slow oscillation stimulation during sleep enhances memory consolidation in rats.
BACKGROUND
The importance of slow-wave sleep (SWS), hallmarked by the occurrence of sleep slow oscillations (SO), for the consolidation of hippocampus-dependent memories has been shown in numerous studies. Previously, the application of transcranial direct current stimulation, oscillating at the frequency of endogenous slow oscillations, during SWS enhanced memory consolidation for a hippocampus dependent task in humans suggesting a causal role of slowly oscillating electric fields for sleep dependent memory consolidation.


OBJECTIVE
Here, we aimed to replicate and extend these findings to a rodent model.


METHODS
Slow oscillatory direct transcranial current stimulation (SO-tDCS) was applied over the frontal cortex of rats during non-rapid eye movement (NREM) sleep and its effects on memory consolidation in the one-trial object-place recognition task were examined. A retention interval of 24 h was used to investigate the effects of SO-tDCS on long-term memory.


RESULTS
Animals' preference for the displaced object was significantly greater than chance only when animals received SO-tDCS. EEG spectral power indicated a trend toward a transient enhancement of endogenous SO activity in the SO-tDCS condition.


CONCLUSIONS
These results support the hypothesis that slowly oscillating electric fields causal affect sleep dependent memory consolidation, and demonstrate that oscillatory tDCS can be a valuable tool to investigate the function of endogenous cortical network activity.
University of Lübeck, Department of Neuroendocrinology, Lübeck, Germany.
Sonja
S
Binder
University of Lübeck, Department of Neuroendocrinology, Lübeck, Germany.
Karolin
K
Berg
University of Lübeck, Graduate School for Computing in Medicine and Life Sciences, Lübeck, Germany; University of Lübeck, Institute for Robotics and Cognitive Systems, Lübeck, Germany.
Fernando
F
Gasca
The City College of The City University of New York, Department of Biomedical Engineering, New York, USA.
Belen
B
Lafon
The City College of The City University of New York, Department of Biomedical Engineering, New York, USA.
Lucas C
LC
Parra
University of Lübeck, Department of Neuroendocrinology, Lübeck, Germany; University of Tübingen, Institute of Medical Psychology and Behavioral Neurobiology, Tübingen, Germany.
Jan
J
Born
University of Lübeck, Department of Neuroendocrinology, Lübeck, Germany; University of Lübeck, Graduate School for Computing in Medicine and Life Sciences, Lübeck, Germany. Electronic address: marshall@uni-luebeck.de.
Lisa
L
Marshall
D000818:Animals; D005625:Frontal Lobe / Q000502:physiology; D006624:Hippocampus / Q000502:physiology; D008297:Male; D057567:Memory, Long-Term / Q000502:physiology*; D023421:Models, Animal; D051381:Rats; D020318:Rats, Long-Evans; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D065908:Transcranial Direct Current Stimulation / Q000379:methods*
EEG; Memory consolidation; Sleep; Slow oscillation stimulation; tDCS