Abstract
During sleep, new memories undergo a gradual transfer from the hippocampus (HPC) to the neocortex (NC). Precisely timed neural oscillations interacting within and between these brain structures are thought to mediate this sleep-dependent memory consolidation. Although slow oscillations (SOs), sleep spindles, and ripples have received the most attention, exactly which sleep oscillations instantiate the HPC-NC dialog, and via what mechanisms, remains elusive. Employing invasive electroencephalography in 10 neurosurgical patients across a full night of sleep, we identified three broad classes of phase-based HPC-NC communication. First, we observed interregional phase synchrony for non-rapid eye movement (NREM) spindles, N2 and rapid eye movement (REM) theta, and N3 beta activity. Second, we found asymmetrical N3 cross-frequency coupling between HPC SOs and NC activity spanning the delta to ripple bands, but not for the opposite direction. Lastly, NREM theta and spindle synchrony were themselves modulated by HPC SOs. These novel forms of phase-based interregional communication emphasize the role of HPC SOs in the HPC-NC dialog, and may offer a physiological basis for the sleep-dependent reorganization of mnemonic content.