Mechanistic description
Auditory 40 Hz entrainment applied during NREM sleep consolidates temporal coupling between hippocampal theta oscillations (4-8 Hz) and cortical gamma (30-100 Hz), strengthening CA3→CA1→EC circuit coherence through LTP-like mechanisms involving NMDA receptor activation. This hypothesis generates directly measurable electrophysiological readouts, has established correlative evidence linking coupling restoration to memory rescue (Mably 2020), and represents the most translation-ready mechanism given non-invasive EEG endpoints. The primary vulnerability is that ‘repair’ is defined by the therapeutic outcome itself, making the causal direction difficult to establish without Granger causality or perturbation experiments.
Evidence for (3)
Sleep-dependent gamma entrainment restores hippocampal-cortical coordination
Theta-gamma coupling deficits precede memory impairments in 5xFAD mice
Restored coupling correlates with spatial memory rescue
Evidence against (2)
Evidence is largely correlative; causal direction (entrainment→coupling→memory) not definitively established
PAC metrics can conflate signal from distinct sources; hippocampal PAC measured from scalp EEG is indirect