Definition: A ripple (or sharp-wave ripple, SWR) is a brief, high-frequency oscillatory event in the brain’s local field potential, typically occurring in the 80–200 Hz range. It is most prominently observed in the hippocampus during offline states such as sleep, quiet wakefulness, or memory recall.

• Frequency: ~80–120 Hz in humans; ~140–200 Hz in rodents.
• Duration: 50–150 milliseconds.
• Location: Hippocampus (CA1), entorhinal cortex, and medial temporal lobe; recently reported in neocortex.
• Co-occurrence: Typically accompanies a sharp wave (SWR), reflecting synchronous depolarization from CA3 to CA1.

• Memory consolidation: Supports reactivation of neuronal ensembles representing recent experiences.
• Replay of experience: Sequences of place cells or event-related patterns are replayed during ripples.
• Interregional communication: Synchronizes hippocampal activity with prefrontal cortex and other memory-related areas.

• Sleep: Especially during slow-wave sleep (SWS), promoting consolidation of declarative memories.
• Quiet rest: Ripples emerge after learning, during passive states.
• Movie-watching and naturalistic experience: Ripple-like activity has been detected at event boundaries and salient within-event moments in recent intracranial EEG studies.

• Cognitive neuroscience: Central to models of systems consolidation and memory replay.
• Neurological disorders:
  • Abnormal ripples are seen in epilepsy (e.g., high-frequency oscillations used as biomarkers).
  • Disruption of ripple dynamics may underlie memory deficits in aging and Alzheimer's disease.
• Brain-computer interfaces (BCI): Ripples are being explored as biomarkers for decoding memory states or intent.

• Sharp-wave ripple (SWR): The combined low-frequency sharp wave and high-frequency ripple; foundational for memory reactivation.
• Replay: The sequential reactivation of neurons during ripple events.
• Hippocampal-cortical dialogue: Ripple timing facilitates inter-regional communication for consolidation.

see Sharp waves and ripples