Gradual emergence of spontaneous correlated brain activity during fading of general anesthesia in rats: Evidences from fMRI and local field potentials

Ruggero G Bettinardi,Núria Tort-Colet,Marcel Ruiz-Mejias,Maria V Sanchez-Vives,Gustavo Deco

doi:10.1016/j.neuroimage.2015.03.037

Abstract

Intrinsic brain activity is characterized by the presence of highly structured networks of correlated fluctuations between different regions of the brain. Such networks encompass different functions, whose properties are known to be modulated by the ongoing global brain state and are altered in several neurobiological disorders. In the present study, we induced a deep state of anesthesia in rats by means of a ketamine/medetomidine peritoneal injection, and analyzed the time course of the correlation between the brain activity in different areas while anesthesia spontaneously decreased over time. We compared results separately obtained from fMRI and local field potentials (LFPs) under the same anesthesia protocol, finding that while most profound phases of anesthesia can be described by overall sparse connectivity, stereotypical activity and poor functional integration, during lighter states different frequency-specific functional networks emerge, endowing the gradual restoration of structured large-scale activity seen during rest. Noteworthy, our in vivo results show that those areas belonging to the same functional network (the default-mode) exhibited sustained correlated oscillations around 10Hz throughout the protocol, suggesting the presence of a specific functional backbone that is preserved even during deeper phases of anesthesia. Finally, the overall pattern of results obtained from both imaging and in vivo-recordings suggests that the progressive emergence from deep anesthesia is reflected by a corresponding gradual increase of organized correlated oscillations across the cortex.

Highlights

The intrinsic complexity of brain organization allows the emergence of a wide range of different activity regimes, referred to as brain states
We observed a certain degree of heterogeneity depending on the regions of interest (ROIs), but we observed an overall increase in BOLD variability as the effect of anesthesia diminished in time
To check for this possibility, we took as representative four ROIs whose BOLD signals showed the highest correlation during the light period and compared the corresponding BOLD distributions obtained from the two levels of anesthesia

Summary

Introduction

The intrinsic complexity of brain organization allows the emergence of a wide range of different activity regimes, referred to as brain states. A significant portion of brain structural architecture is phylogenetically conserved in vertebrates (Striedter, 2005), with fundamental similarities among mammals (Hofman, 1989). This inter-species similarity in anatomical connectivity gives rise to the emergence of comparable patterns of organized activity, usually referred to as functional networks (for a review see Park and Friston, 2013). Our results confirmed that different states of anesthesia are mirrored by broad changes in the underlying functional organization that occur at different spatio-temporal levels, and that the state-related emergence of largescale functional networks is sustained by inter-areal correlated oscillations at specific frequencies.

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