OP 1. Boosting sleep slow oscillations by oscillatory transcranial direct current stimulation enhances memory consolidation in rats

• Published in: Clinical neurophysiology 2013-10, Vol.124 (10), p.e54-e55
• Main Authors: Binder, S, Berg, K, Gasca, F, Born, J, Marshall, L
• Format: Article
• Language: English
• Subjects: Neurology
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2013.04.068

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. 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 human subjects and suggested a causal role of SOs for sleep dependent memory consolidation ( Marshall et al., 2006 ). Objectives 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 slow-wave sleep (SWS) and its effects on memory consolidation in the one-trial object-place recognition task (OPR) were examined. The OPR is a spatial memory task, and has been shown to depend critically on intact hippocampal function ( Bussey et al., 2000; Mumby et al., 2002 ). It does not involve stressful procedures or food deprivation; it is based on the rodents’ natural behavior, i.e., novelty preference ( Ennaceur et al., 1997 ) and allows for intra-subject testing for stimulation and sham conditions. Previous findings showed the dependency of this task on sleep containing a large amount of slow wave activity within the retention interval ( Binder et al., 2012; Inostroza et al., 2012 ). In a within subject design, 12 rats received one so-tDCS over the frontal cortex and one sham-tDCS session immediately after learning during early SWS. 24 h after learning, the test session in the OPR task took place to investigate the effects of so-tDCS on long-term memory. Results As depicted in Fig. 1 , animals were only able to solve the task following so-tDCS, but failed to do so in the sham condition lacking so-tDCS. EEG spectral power indicated a transitory enhancement of endogenous SO activity after cessation of so-tDCS. Conclusion We conclude that SO play a causal role for sleep dependent memory consolidation, and state that oscillatory tDCS is a highly valuable tool to further investigate the function of endogenous cortical network activity.