Schedule of Events | Symposia

Postdoctorial Fellowship Award Winner

Hippocampal ripples across different brain states

Poster Session F - Tuesday, April 1, 2025, 8:00 – 10:00 am EDT, Back Bay Ballroom/Republic Ballroom

Pin-Chun Chen¹ (pcchen.sleep@gmail.com), Jenny Stritzelberger², Katrin Walther², Hajo Hamer², Bernhard Staresina¹; ¹University of Oxford, ²Universitatsklinikum Erlangen

High-frequency bursts in the hippocampus, known as ripples, are thought to support memory consolidation during "offline" states, such as sleep. Recently, human hippocampal ripples have also been observed during "online" memory tasks. However, ripple attributes and their functional significance across states remain unclear. We investigated ripple characteristics across brain states using intracranial EEG from the hippocampus of nineteen participants undergoing invasive monitoring for epilepsy surgery. We quantified four ripple attributes: (1) density, (2) duration, (3) amplitude, and (4) peak frequency. We detected ripples across 5 sleep stages and 3 awake states, all recorded on the same day: (i) slow-wave sleep (SWS), (ii) stage 2 sleep, (iii) stage 1 sleep, (iv) rapid-eye-movement (REM) sleep (v) wake-after-sleep-onset (WASO), (vi) awake resting, (vii) a motor learning task, (viii) an attention task. Linear mixed-effects models with Bonferroni corrections were built, with brain state as a fixed effect, participant and hippocampal contacts as random effects. Results reveal that ripple density is by far highest during SWS and lower during all awake states compared to sleep. Likewise, ripple duration is longest in SWS and shortest during active motor learning. Finally, microwire data reveal strongest ripple-locked increases in neural firing rates during SWS. These findings suggest that ripple characteristics vary across states and reinforce their role as markers of offline neural processing, particularly during deep sleep.

Topic Area: METHODS: Electrophysiology