Figure 2. Spindle timing and information transfer.

(A) 45 seconds of NREM sleep (electrode Cz, black) with superimposed spindle oscillations (in red). Arrows highlight distinct signatures of NREM sleep, including (left to right) spindles nested in SOs, uncoupled spindles as well as two examples of aperiodic states. Note, spindles exhibit a second-order temporal structure and re-occur rhythmically every ~3–6 seconds. (B) Schematic of how the different NREM states might contribute to memory consolidation. Note, it is currently unclear if coupled and uncoupled spindles are functionally distinct and it is unknown in which sequence oscillatory and aperiodic states alternate. Left: Coupled SO-spindles trigger bidirectional hippocampal-neocortical interactions (as indicated by the arrows). Center: During aperiodic states, networks might switch to local processing to enable transformation of mnemonic content (arrows indicate local processing loops). Right: Highly synchronized population activity is necessary to mediate synaptic plasticity to enable long-term neocortical storage. (C) Left: Auditory-triggered disruption of the information transfer. A sound was presented directly after an oscillatory (grey box) event (0.25s, early) or with a longer temporal delay (2.5s, late). Right: Only early sound presentation selectively disrupted information transfer as indicated by an increased forgetting rate. Panel C is reproduced with permission from [22].