POSTER DETAILS e-POSTER QR CODE RELATED POSTERS

POSTER DETAILS

Conjunctive theta- and ripple-frequency oscillations across hippocampal strata of foraging rats

Pavithraa Seenivasan, Reshma Basak, Rishikesh Narayanan

Date / Location: 18 March / II-088
Brain rhythms have been postulated to play central roles in animal cognition. A prominently reported dichotomy of hippocampal rhythms exclusively assigns occurrences of theta-frequency (4–12 Hz) oscillations to exploratory behavior and rapid eye movement (REM) sleep, and of ripple-frequency (120–250 Hz) oscillations to wakeful rest and non-REM sleep. However, due to their differential expression across hippocampal strata, reports of such exclusivity demand validation through simultaneous multi-strata recordings. Here, we assessed co-occurrence of the two oscillations in multi-channel recordings of extracellular potentials across hippocampal strata from rats foraging an open-field arena. We detected all ripple events from an identified stratum pyramidale (SP) channel based on rigorous thresholds relating to the spectro-temporal and spatial characteristics of ripples. We then defined θ epochs based on theta oscillations detected from each of the different channels spanning the SP to the stratum lacunosum moleculare (SLM) through the stratum radiatum (SR). Across rats, we found 10–20% of ripple events to co-occur with θ epochs identified from SR/SLM channels, defined here as θ-ripples. Strikingly, when θ epochs were identified from the SP channel, there was no such co-occurrence, emphasizing that the reported behavioral dichotomy is merely a reflection of conclusions from single-channel recordings targeting the SP. We assessed the behavioral state of rats during ripple events and found a distribution of ripple kinds: e-θ, i-θ, e-Nonθ, and i-Nonθ (e/i: exploratory vs. immobile behavior; θ/Nonθ: co-occurring theta oscillations detected vs. not detected in SR/SLM), with i-Nonθ ripples showing the highest detection frequency. Finally, we found a strong θ-phase preference of θ-ripples within the third quadrant [3pi/2–2pi]. Together, our analyses provide direct quantitative evidence for the occurrence of ripple events nested within θ oscillations. Given the established roles of these oscillations, our analyses suggest concomitant encoding and consolidation processes during different behavioral states.

e-POSTER

ℹ️ e-poster expected to become available by the author soon
e-POSTER

QR CODE

POSTERS YOU MIGHT BE INTERESTED IN