P205 High-frequency oscillations in primate visual areas: Critical insights into neural population dynamics or mere spike artifacts? Katarína Studeničová*1, Aitor Morales-Gregorio1, Karolína Korvasová1
1Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
*Email: katarina.studenicova@matfyz.cuni.cz
Introduction Short bursts of high-gamma frequency oscillations (80-150 Hz) resembling hippocampal ripples were to date observed in several cortical areas [1-4]. However, their function and link to memory processes are unclear. The goal of our work is to describe the relationship between the high-gamma bursts, referred to as cortical ripples, and neuronal spiking activity in the same cortical location under different levels of drowsiness. Methods We analyze a dataset of the resting state activity consisting of 4 macaque monkeys ([5,6], and additional data provided by the authors), each having 16 Utah arrays implanted in visual areas V1, V2, V4, and IT. Monkeys sat in a dark room, and the vigilance of the recorded animals changed, ranging from fully alert to drowsy and light sleep. Raw traces were downsampled and filtered to the ripple band signal (80-150 Hz), and spikes were sorted. Short high-amplitude oscillatory bursts present in the ripple band, further referred to as cortical ripples, were detected by the standard double thresholding methods, and additionally confirmed by spectral analysis and surrogate methods.
Results During the alert eyes open states without strong visual input, the dynamic of a network is unorganized in both space and time. However, with increasing drowsiness, the network falls into a global upstate-downstate regime. Upstates are strongly visible mainly in V1 and V2, and less organized in V4 and IT, possibly reflecting a different organizational structure of higher cortical areas. In all brain states, cortical ripples are accompanied by spiking activity. In general, spikes are locked to the phase of the ripple band. Most are locked to the trough, however, we also found cells preferring peaks of the oscillatory signal. We detail these findings further by describing a variety of spiking preferences with respect to the ripple band.
Discussion To the best of our knowledge, we are the first to uncover the global organization of high-frequency oscillatory activity in the macaque visual areas during resting state, spanning large horizontal distances with intracortical recording precision. We prove the existence of cortical ripples in all the areas covered (previously literature only addressed V1 and V4) and describe the relationship between spikes and cortical ripples with respect to various brain states. We detail our findings by area-wise description, highlighting crucial differences. This work aims to bridge gaps between various recording techniques by providing a detailed view of network states underlying high-frequency oscillatory bursts.
Acknowledgements This work received funding from the Charles University grant PRIMUS/24/MED/007; and the Programme Johannes Amos Comenius (OP JAK) under the project 'MSCA Fellowships CZ - UK3' (reg. n. CZ.02.01.01/00/22\_010/0008220). References [1] https://doi.org/10.1523/JNEUROSCI.0742-22.2022 [2] https://doi.org/10.7554/eLife.68401 [3] https://doi.org/10.1093/brain/awae159 [4] https://doi.org/10.1073/pnas.2210698120 [5] https://doi.org/10.1038/s41597-022-01180-1 [6] https://doi.org/10.1016/j.neuron.2024.12.003
