Abstract
Anesthesia induces a reconfiguration of the repertoire of functional brain states leading to a high function-structure similarity. However, it is unclear how these functional changes lead to loss of consciousness. Here we suggest that the mechanism of conscious access is related to a general dynamical rearrangement of the intrinsic hierarchical organization of the cortex. To measure cortical hierarchy, we applied the Intrinsic Ignition analysis to resting-state fMRI data acquired in awake and anesthetized macaques. Our results reveal the existence of spatial and temporal hierarchical differences of neural activity within the macaque cortex, with a strong modulation by the depth of anesthesia and the employed anesthetic agent. Higher values of Intrinsic Ignition correspond to rich and flexible brain dynamics whereas lower values correspond to poor and rigid, structurally driven brain dynamics. Moreover, spatial and temporal hierarchical dimensions are disrupted in a different manner, involving different hierarchical brain networks. All together suggest that disruption of brain hierarchy is a new signature of consciousness loss.
Highlights
Recent studies suggest dynamical disruptions on brain activity during general anesthesia, sleep and disorders of consciousness (Dehaene & Changeux, 2011; Mashour et al, 2020)
The global values of hierarchical organization indicate similar global organization under anesthesia, while local analyses on which areas habit hierarchical levels inform on the different ways that anesthetics affect spatial and temporal aspects of that organization
This is in line with the idea that disruptions in long-distance network dynamics are a common signature of anesthesia-induced loss of consciousness, but adding the breakdown of hierarchical organization and its two dimensions, space and time
Summary
Recent studies suggest dynamical disruptions on brain activity during general anesthesia, sleep and disorders of consciousness (Dehaene & Changeux, 2011; Mashour et al, 2020). During anesthesia-induced loss of consciousness, the resting-state brain activity is shifted toward a poor repertoire of rigid functional patterns with higher similarity to structural connectivity. A finding that was generalized to different anesthetic agents (Uhrig et al, 2018) and applied to classify different categories of chronic loss of consciousness (Demertzi et al, 2019). This dynamical disruption at long-distance networks might be the common fingerprint of all different types of loss of consciousness (anesthesia-induced, injuriesinduced loss of consciousness and sleep)
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