During NREM sleep, memory consolidation runs as a nested oscillatory procedure across three timescales. Slow oscillations (~0.75 Hz) set cortical excitability windows by alternating between active up-states and silent down-states. Sleep spindles (12–15 Hz) fire preferentially during SO up-states, when the thalamocortical loop is most excitable. Sharp-wave ripples (~90 Hz) nest within spindle troughs — brief hippocampal events carrying compressed sequence replays at roughly 20× real speed.
The coupling across these three scales is the consolidation procedure. Switch to uncoupled to see the same three oscillations with independent timing. The difference between the two views is the difference between an orchestrated sequence and three signals sharing a channel.
Click anywhere on the overview to move the playhead. The lower panel zooms into a 2-second window at that position, where individual spindle cycles (~77ms/cycle) and ripple bursts (~80ms) become visible.
Slow oscillation (SO): ~0.75 Hz cortical rhythm. Shaded regions mark up-states — periods of sustained depolarization and active firing. Down-states are near-silent. In the coupled condition, spindles appear only within up-states. Switching to uncoupled shows spindles distributed randomly across both up- and down-states, making clear how much the coupling constrains spindle timing.
Spindle bursts: 12–15 Hz thalamocortical oscillations, 0.5–2 seconds long. Generated by thalamic reticular nucleus feedback loops. Each spindle creates a series of troughs — the moments of least cortical excitation, which is paradoxically when hippocampal input arrives. The 2015 Staresina et al. intracranial recording study found ripple power increased 17.9% within 500ms of spindle center, with successive ripples tracking spindle frequency precisely at 14.5 Hz intervals.
Sharp-wave ripples: ~80–100 Hz, lasting ~80ms. Generated in CA3→CA1 hippocampus. Each event replays a compressed sequence — a few seconds of recent experience encoded at roughly 20× speed. In the coupled condition, ripples arrive at spindle troughs, delivered to cortex during spindle-gated windows. The person is unconscious throughout. The delivery address is open from outside; from inside, nothing is accessible.
What the simulation doesn't show: the content of any individual replay, whether a particular transfer succeeds, variability in spindle placement within up-states, the precise 14.5 Hz ripple-to-ripple coupling tracking spindle phase, or which cortical neurons receive which replay. The coupling shown is schematic — actual physiology is probabilistic and messier. The procedure runs; the outcome is not visible from inside the procedure.