EEG sigma and slow-wave activity during NREM sleep correlate with overnight declarative and procedural memory consolidation

Previous studies suggest that sleep-specific brain activity patterns such as sleep spindles and electroencephalographic slow-wave activity contribute to the consolidation of novel memories. The generation of both sleep spindles and slow-wave activity relies on synchronized oscillations in a thalamo-cortical network that might be implicated in synaptic strengthening (spindles) and downscaling (slow-wave activity) during sleep. This study further examined the association between electroencephalographic power during non-rapid eye movement sleep in the spindle (sigma, 1216 Hz) and slow-wave frequency range (0.13.5 Hz) and overnight memory consolidation in 20 healthy subjects (10 men, 27.1 +/- 4.6 years). We found that both electroencephalographic sigma power and slow-wave activity were positively correlated with the prepost-sleep consolidation of declarative (word list) and procedural (mirror-tracing) memories. These results, although only correlative in nature, are consistent with the view that processes of synaptic strengthening (sleep spindles) and synaptic downscaling (slow-wave activity) might act in concert to promote synaptic plasticity and the consolidation of both declarative and procedural memories during sleep.