Memory consolidation is thought to involve a hippocampo-cortical dialogue supported by oscillations during sleep, to stabilize labile memory traces for stable long-term storage. However, direct evidence supporting this hypothesis is lacking. A first set of experiments conducted during my PhD showed that hippocampo-cortical oscillatory coupling selectively increased following training on a task leading to memory consolidation, but not following time-limited training on the same task that resulted in weak, non-consolidated memory traces.
We then designed a novel closed-loop stimulation protocol allowing for the dynamic enhancement of hippocampo-cortical couping during sleep following time-limited training. Reinforcing the endogenous coordination between hippocampal sharp wave-ripples, cortical delta waves and spindles by timed electrical stimulation resulted in high recall performance after a 24h delay, contrary to control rats that performed at chance levels. These results provide the first direct evidence for a causal role of a hippocampo-cortical dialogue during sleep in memory consolidation, and indicates that the underlying mechanism involves a fine-tuned coordination between sharp wave-ripples, delta waves and spindles.
- Nakamura, N.H., Flasbeck, V., Maingret, N., Kitsukawa, T., Sauvage, M.M. Proximodistal Segregation of Nonspatial Information in CA3: Preferential Recruitment of a Proximal CA3-Distal CA1 Network in Nonspatial Recognition Memory. The Journal of Neuroscience. 33:11506-14.
Maingret, N., Girardeau, G., Todorova, R., Goutierre, M. & Zugaro, M. Hippocampo-cortical coupling mediates memory consolidation during sleep. Nature Neuroscience. doi:10.1038/nn.4304