Abstract
Consciousness is considered a result of specific neuronal processes and mechanisms in the brain. Various suggested neuronal mechanisms, including the information integration theory (IIT), global neuronal workspace theory (GNWS), and neuronal construction of time and space as in the context of the temporospatial theory of consciousness (TTC), have been laid forth. However, despite their focus on different neuronal mechanisms, these theories neglect the energetic-metabolic basis of the neuronal mechanisms that are supposed to yield consciousness. Based on the findings of physiology-induced (sleep), pharmacology-induced (general anesthesia), and pathology-induced [vegetative state/unresponsive wakeful syndrome (VS/UWS)] loss of consciousness in both human subjects and animals, we, in this study, suggest that the energetic-metabolic processes focusing on ATP, glucose, and γ-aminobutyrate/glutamate are indispensable for functional connectivity (FC) of normal brain networks that renders consciousness possible. Therefore, we describe the energetic-metabolic predispositions of consciousness (EPC) that complement the current theories focused on the neural correlates of consciousness (NCC).
Highlights
Our brain is energy hungry and consumes about 20–25% of the energy of the whole body despite representing only 2% of the body mass
As general anesthesia typically induces a 55% reduction in the whole-brain glucose metabolism in humans (Laaksonen et al, 2018), non-rapid eye movement (NREM) sleep a 23% reduction (Guye et al, 2010), and coma a 60% reduction (Buchsbaum et al, 1989), Shulman proposes that the global energy reduction is responsible for the loss of consciousness (Shulman et al, 2009), and that the measurement of global cerebral metabolic rate of glucose (CMRglc) could be used as an approach to discriminate a conscious state from an unconscious state
Thanks to classical investigations of Shulman focusing on the relationships between the brain metabolism and neural activity and neurotransmission, we have identified that normal energy metabolism may provide sufficient ATP to energize synaptic protein synthesis and maintain the information processing power of the brain
Summary
Our brain is energy hungry and consumes about 20–25% of the energy of the whole body despite representing only 2% of the body mass Most of this energy, around 80–90%, is spent for its spontaneous activity, as measured in the resting state, that is, without any specific task demands. Few studies on sleep (Rempe and Wisor, 2014), anesthesia (Laaksonen et al, 2018), and vegetative state/unresponsive wakefulness state (VS/UWS) (Garcia-Panach et al, 2011) have shown decreased glucose metabolism in various brain regions and/or networks. These findings indicate that an unconscious state has a distinct energetic signature from an awake state. Neuroenergetics may play a crucial role in consciousness (Shulman et al, 2009)
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