P182 Computational aspects of microarousals during awakening from anesthesia
Arnau Manasanch*1,2, Leonardo Dalla Porta1, Melody Torao-Angosto1, Maria V. Sanchez-Vives1,3 1Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain 2Facultat de Medicina I Ciències de la Salut, Universitat de Barcelona, 08036 Barcelona, Spain 3ICREA, Passeig Lluís Companys 23, 08010 Barcelona, Spain
*Email:manasanch@clinic.cat
Introduction The study of brain states is fundamental to understanding consciousness and its neural mechanisms [1,2]. Both sleep and anesthesia provide valuable models for investigating and characterizing brain states and their transitions [3,4,5]. While extensive research has characterized Microarousals (MAs), brief wake-like periods of brain activity, in sleep [6], these remain almost unexplored during anesthesia. Emerging evidence suggests that these transient events may be modulated by an infraslow rhythm [7,8,9], influencing arousal dynamics during emergence from anesthesia. Here, we investigate the dynamics of MAs during anesthetic emergence using local field potential (LFP) recordings from anesthetized rats, shedding light on infraslow modulation of transient arousals.
Methods
To obtain long-term LFP recordings in freely moving Lister-Hooded rats (6–10 months old), electrodes were chronically implanted 600 µm deep in the cortex. EMG was recorded from the neck muscle. After post-surgical care, animals underwent five days of handling before recordings. LFPs were recorded during anesthesia induction and emergence. The protocol was the same used in [10]. Briefly,each subject received a single shot of intraperitoneal anesthesia consisting of ketamine (20-40 mg/kg) and medetomidine (0.15-0.3 mg/kg).Cortical activity was monitored from wakefulness to full emergence from anesthesia. Experiments followed Spanish and EU regulations and were approved by the Ethics Committee of the Universitat de Barcelona (287/17 P3). Results After remaining in the slow oscillatory state, characterized by alternating Up (high firing) and Down (silent) periods, for 2–3 hours, the brain dynamics abruptly transitioned to a state dominated by fast oscillations (~6 Hz) and wake-like microarousals. As anesthesia wore off, MAs progressively increased in duration. This transition appeared to be modulated by an infraslow oscillation during a steady state period (~0.14 Hz), which gradually slowed (reaching ~0.04 Hz) in the progression towards wakefulness. Analysis of MAs across subjects reveals a consistent trend of increasing duration of the microarousals over time, with power-law distributions observed in the duration of MAs. These distributions show an average exponent of 2.33±0.36, suggesting that microarousals exhibit characteristic scaling behavior across different subjects.
Discussion Our findings suggest that the increasing duration of microarousals (MAs) as anesthesia progresses reflect a gradual transition toward wakefulness, with dynamics that share properties with sleep awakening.The power-law behavior in MA duration indicates a scale-invariant process, a hallmark of self-organized criticality. This model provides a new understanding of the microarchitecture of anesthesia, offering a window into controlled microarousals and the network dynamics from unconsciousness to consciousness.
Acknowledgements The EU Horizon 2020 Framework Programme for Research and Innovation under the Specific Grant Agreement No. 945539 (Human Brain Project SGA3); INFRASLOW PID2023-152918OB-I00 funded by MICIU / AEI / 10.13039/501100011033/FEDER. Co-funded by Departament de Recerca i Universitats de la Generalitat de Catalunya (AGAUR 2021-SGR-01165). IDIBAPS is funded by the CERCA program (Generalitat de Catalunya). References [1]https://doi.org/10.1038/nrn3084 [2]https://doi.org/10.1016/j.tins.2023.04.001 [3]https://doi.org/10.1126/science.8235588
