Theory 038/Mind & Behaviour /Sleep and memory
Spindles Gate Memory at a Density
Spindles are counted and measured. The useful variable may be how often they occur.
Sleep spindles support memory consolidation only above a density threshold, so the number per minute matters more than their individual amplitude, and boosting amplitude without density should not help.
01The evidence
Spindle density correlates with overnight retention in many studies, while amplitude correlations are weaker and less consistent.
02The tension
Spindle amplitude is the easier measure and is often used as the summary. It predicts retention poorly, and the discrepancy is usually attributed to electrode placement.
03The mechanism
A spindle opens a window for plasticity. One window per minute is not enough to consolidate a night's learning; the windows must recur often enough to capture the material.
That makes density the controlling variable, and predicts that increasing density should improve retention while increasing amplitude at constant density should not.
04What this is not
Amplitude accounts treat each spindle as more or less powerful. This treats spindles as windows whose number matters.
05Predictions
- P1Retention should track density better than amplitude.
- P2Amplitude boosts at constant density should not help.
- P3Density should predict across nights within subjects.
06Refutation
Retention tracking amplitude at controlled density would restore the amplitude account.
07What it changes
It would change how sleep is measured for memory.