Post by Admin on Jun 14, 2022 13:00:40 GMT
Consciousness as a Physical Process Caused by the Organization of Energy in the Brain
www.frontiersin.org/articles/10.3389/fpsyg.2018.02091/full
To explain consciousness as a physical process we must acknowledge the role of energy in the brain. Energetic activity is fundamental to all physical processes and causally drives biological behavior. Recent neuroscientific evidence can be interpreted in a way that suggests consciousness is a product of the organization of energetic activity in the brain. The nature of energy itself, though, remains largely mysterious, and we do not fully understand how it contributes to brain function or consciousness. According to the principle outlined here, energy, along with forces and work, can be described as actualized differences of motion and tension. By observing physical systems, we can infer there is something it is like to undergo actualized difference from the intrinsic perspective of the system. Consciousness occurs because there is something it is like, intrinsically, to undergo a certain organization of actualized differences in the brain.
Introduction
“If mental processes are indeed physical processes, then there is something it is like, intrinsically, to undergo certain physical processes. What it is for such a thing to be the case remains a mystery.”
(Nagel, 1974)
The philosopher Thomas Nagel summarized one of our greatest intellectual challenges: how to explain mental processes as physical processes. The aim of this paper is to outline a principle according to which consciousness could be explained as a physical process caused by the organization of energy in the brain1.
Energy is fundamentally important in all physical processes (Lotka, 1922; Schrödinger, 1944; Heisenberg, 1958; Boltzmann, 1886). As the biophysicist Harold Morowitz (1979) put it: “the flow of energy through a system acts to organize that system.” Light, chemical reactions, electricity, mechanical work, heat, and life itself can all be described in terms of energetic activity (Chaisson, 2001; Morowitz and Smith, 2007; Smil, 2008) as can metabolic processes in the body and brain (Magistretti, 2008; Perez Velazquez, 2009). It is surprising, therefore, that energy receives relatively little attention in neuroscientific and psychological studies of consciousness. Leading scientific theories of consciousness do not reference it (Crick and Koch, 2003; Edelman et al., 2011; Dehaene, 2014; Oizumi et al., 2014), assign it only a marginal role (Hameroff and Penrose, 2014), or treat it as an information-theoretical quantity (Friston, 2013; Riehl et al., 2017). If it is discussed, it is either as a substrate underpinning higher level emergent dynamics (Deacon, 2013) or as powering neural information processing (Sterling and Laughlin, 2017).
This lack of attention is all the more surprising given that some of the pioneers of neurobiology, psychology, and physiology found a central place for energy in their theories, including Hermann von Helmholtz (in Cahan, 1995), Gustav Fechner (1905), Sigmund Freud (Gay, 1988), William James (James, 1907), and Charles Sherrington (1940)2. There are, however, signs that attention is turning again to energetic or thermodynamic-related theories of consciousness in various branches of science (Deacon, 2013; Collell and Fauquet, 2015; Annila, 2016; Street, 2016; Tozzi et al., 2016; Marchetti, 2018) and in philosophy of mind (Strawson, 2008, 2017).
The present paper builds on this work by proposing that energy, and the related properties of force and work, can be described as actualized differences of motion and tension, and that – in Nagel’s phrase – ‘there is something it is like, intrinsically, to undergo’ actualized differences. Recent neuroscientific evidence suggests that consciousness is a product of the way energetic activity is organized in the brain. Following this evidence, I propose that we experience consciousness because there is something it is like, intrinsically, to undergo a certain organization of actualized differences in the brain.
Several researchers have tackled the problem of consciousness by treating the brain in principle as a neural information processor (e.g., Tononi et al., 2016; Dehaene et al., 2017; Ruffini, 2017). I will argue that the governing principle of the brain at the neural level is not information processing but energy processing. The information-theoretic approach to measuring and modeling brain activity, however, can usefully complement the energetic approach outlined here.
Consciousness and Energy in the Brain
We do not fully understand the biological function of energy in the brain or how it relates to the presence of consciousness in the person3. Given that the human brain accounts for only 2% of the body’s mass it demands a large portion of the body’s total energy budget, some 20% (Laughlin, 2001; Magistretti and Allaman, 2013). Most of this energy is derived from the oxidization of glucose supplied to the cerebral tissue through the blood. Roy and Sherrington were the first to propose a direct correspondence between changes in cerebral blood flow and functional activity (Roy and Sherrington, 1890). Many features of human brain anatomy, such as the number of blood vessels per unit of space, the lengths of neural connections, the width of axons, and even the ratio of brain to stomach size are thought to be determined by the high metabolic demands associated with complex cognitive processing (Allen, 2009).
For many neuroscientists, the main function of energy in the brain is to fuel neural signaling and information processing (Magistretti, 2013); energy supply is seen as a constraint on the design and operation of the brain’s computational architecture (Laughlin, 2001; Hall et al., 2012; Sterling and Laughlin, 2017). It has been calculated, for example, that the rate of energy supply available to the human brain places an upper ‘speed limit’ on neural processing of about 1 kHz (Attwell and Gibb, 2005). And Schölvinck et al. (2008) estimated that conscious perception of sensory stimuli increases energy consumption in primate brains by less that 6% compared to energy consumption in the absence of conscious perception4. They attribute this relatively small change to an energy efficient “design strategy” of the brain in which decreases in neural activity play a functional role in information processing as well as increases. Energy, on these accounts, plays no direct role in higher mental processes, like consciousness.
Robert Shulman and colleagues have argued there is a direct connection between energy in the brain and consciousness (Shulman et al., 2009; Shulman, 2013). By studying the progressive loss of behavioral response to external stimulus from wakefulness to deep anesthesia, they found a corresponding reduction and localization of cerebral metabolism (a marker of energy consumption). Therefore, they argue, high global metabolism is necessary for consciousness. However, they are also clear that high global metabolic rates are not sufficient as patients with locked-in-syndrome and those who suffer from some forms of epileptic seizure can register high levels of global brain metabolism without exhibiting the observable behavior that we expect from a conscious person (Shulman, 2013; Bazzigaluppi et al., 2017). Shulman’s thesis has been challenged on several grounds (Seth, 2014). For example, it has been pointed out that behavioral responsiveness may be inadequate as a measure of sentience given that vestiges of consciousness have been detected in people diagnosed as being in a vegetative state with a low cerebral metabolism (Owen et al., 2006). Moreover, some patients who recover from a vegetative state to regain consciousness do so despite having substantially reduced cerebral metabolism compared with normal controls (Laureys et al., 1999; Chatelle et al., 2011).
In recent years there has been a growing interest in intrinsic brain activity (Clarke and Sokoloff, 1999; Raichle, 2011). This background or spontaneous activity occurs in the resting awake state in the absence of external stimulation or directed attention, and its energy demands can greatly exceed those of localized activation due to task performance or attention. The discovery of this so-called ‘dark energy’ in the brain (Raichle, 2010) was greeted with some surprise in the neuroscience community and remains controversial (Morcom and Fletcher, 2007). Work on intrinsic activity led to the identification of a ‘default mode network’ in the brain, an extended set of interconnected regions that uses high levels of energy when a person is in a non-attentive state. Energy use drops significantly in this network when a more cognitively demanding task, such as paying attention to a stimulus, is performed (Shulman et al., 1997; Raichle et al., 2001). Vanhaudenhuyse et al. (2009) reported that connectivity within the default mode network in patients with severe brain-damage deteriorates in proportion to the degree of conscious impairment, suggesting it plays an important role in sustaining consciousness.
Meanwhile, it is somewhat surprising to find that energy use during non-rapid eye movement sleep remains at ∼85% of that in the waking state, while during rapid eye movement sleep it can be as high as in the waking state (Dinuzzo and Nedergaard, 2017). At the same time, consciousness can be minimally sustained with energy use at only 42% of the level that occurs in healthy conscious individuals, suggesting that much cerebral metabolic activity in normal waking states does not directly contribute to consciousness (Stender et al., 2016). Many anesthetic agents are thought to obliterate consciousness because they reduce the global rate of cerebral metabolism (Hudetz, 2012). Administering ketamine, on the other hand, increases brain metabolism yet can still lead to loss of responsiveness (Pai and Heining, 2007). Overall, it seems we find no clear correlation between the total amount of energy used by the brain, or the location where the energy is used, and the level of consciousness detectable in the person.
Consciousness and the Organization of Energetic Processing in the Brain
An alternative, or perhaps complementary, way to think about this issue is in terms of how the energetic activity in the brain is organized rather than its global level or localization. Indeed, this has implicitly been the focus of recent research that aims to provide quantitative measures of consciousness levels. In one study, researchers used transcranial magnetic stimulation (TMS) to send a magnetic pulse through the brains of healthy controls and patients with various states of impaired consciousness (Casali et al., 2013). By measuring how the pulse perturbed the cortex the researchers were able to determine the relative complexity and extent of the pathways through which the pulse propagated and correlate these to levels of consciousness. The researchers calculated a perturbation-complexity index (PCI) that quantified the levels of consciousness present in each person they studied. This method was further validated as a reliable objective measure of levels of consciousness by Casarotto et al. (2016).
The PCI was calculated using data from electroencephalographic (EEG) measurements of the cerebral perturbation following the TMS. Images from the EEG were filtered into binary data that was then analyzed using a Lempel–Ziv algorithm, a commonly used information-theoretical technique in which complexity is measured as a function of data string compressibility, with more complex data strings being less compressible (Ziv and Lempel, 1977; Aboy et al., 2006). Other researchers have developed similar information-theoretical methods for quantifying the complexity of brain activity and levels of consciousness. King et al. (2013) analyzed data from 181 EEG recordings of patients who were diagnosed with varying states of impaired consciousness and applied a measure of weighted symbolic mutual information (wSMI) that sharply distinguished between patients in vegetative state, minimally conscious state, and conscious state.
Although information theoretic tools were being used to analyze and interpret the data in these studies we should note that what was actually being detected by the experimental procedures was not information per se but the organization of energetic activity or processing in the brain. Energetic processing – the processes by which the brain regulates the flow of energy through its structures – is routinely detected at varying degrees of spatial and temporal resolution, either directly or indirectly, by neuroimaging techniques such as positron emission tomography (PET), functional magnetic resonance image (fMRI), and EEG (Niedermeyer and Lopes da Silva, 1987; Bailey et al., 2005; Shulman, 2013). Referring again to the study by Casali et al. (2013), the perturbations from which the PCI was calculated were generated by a pulse of magnetic energy from the TMS and were imaged with EEG that measures electrical voltage differences, that is, fluctuations in energetic potentials between clusters of neurons in the cortex (Niedermeyer and Lopes da Silva, 1987; Hu et al., 2009; Koponen et al., 2015). The PCI and wSMI can therefore be interpreted as measures of the complexity or organization of energetic processing in the brain during the experimental procedures.
Subsequent research has directly investigated the connection between brain metabolism (how the brain regulates energy conversion), brain organization, and levels of consciousness by combining EEG measures with PET, a more specific measure of cerebral metabolism. Chennu et al. (2017) collected data from 104 patients in varying states of conscious impairment using both techniques. By analyzing this data, they determined a metric that discriminated levels of consciousness to a high degree of accuracy. This study built on previous work by Demertzi et al. (2015) that used fMRI to correlate a measure of intrinsic functional connectivity in the brain with levels of consciousness. The PCI method has been further validated by a study combining EEG and 18F-fluorodeoxyglucose (FDG)-PET (Bodart et al., 2017), so reinforcing the link between levels of consciousness and the organization of metabolic activity in the brain.
Current brain imaging methods do not strictly speaking detect information processing5. They do, however, detect changes associated with increases in energy consumption (via fMRI and PET) and fluctuations in electrical potential energy (via EEG), both of which reliably correlate with changes in mental function and behavior. On the basis of what we can observe, the brain operates according to the principle of energetic processing. The evidence discussed above suggests levels of consciousness are determined by the organization of energy processing in the brain rather than on its global level or localization; wakeful conscious states are associated with more complex organization. To understand why this might be we need to consider the concept of energy in more depth.
Energy
The concept of energy that we are familiar with today emerged only slowly from its beginnings in the late eighteenth century. It developed through the study of thermodynamics in the nineteenth century, and then found its place at the center of theories of relativity, quantum mechanics, and cosmology in the twentieth (Coopersmith, 2010). In colloquial usage energy refers to ideas of vigor, vitality, power, activity, and zest. In scientific usage, however, energy is defined as the ability of a system to do work6. Work is defined as the transfer of energy involved in moving an object over a distance by an external force, at least part of which is applied in the direction of the displacement (Duncan, 2002). Scientists and engineers often refer to energy as an abstract property: “Energy is a mathematical abstraction that has no existence apart from its functional relationship to other variables” (Abbott and Van Ness, 1972; Rose, 1986). It is a property that can be converted from one form to another, and in an isolated system the total quantity is conserved (Smil, 2008).
Despite the enormous amount of interest in the physics of energy and its central importance in so many branches of science, its nature remains in many ways mysterious (Feynman, 1963; Smil, 2008; Coopersmith, 2010) and it has been the subject of relatively little philosophical interrogation (Coelho, 2009). Treating energy as an abstract accounting quantity is perfectly satisfactory for many scientific purposes, where there is little reason to question its nature. But if energetic activity plays a significant role in consciousness, as the evidence cited above suggests it might, then its nature deserves closer scrutiny.
The concept of energy in the European intellectual tradition can be traced back to Aristotle who used but never precisely defined the term energeia (ενwww.frontiersin.orgρwww.frontiersin.orgεια) to convey the ideas of action, activity, actuality, being at work, and acting purposefully (Sachs in Aristotle, 2002). Scholars have long debated the best way to translate energeia from ancient Greek. The word ‘energy’ itself has been used, as have ‘activity’ and ‘actuality,’ but ‘being-at-work’ is currently favored, partly due to energeia’s roots in ergon, the ancient Greek for work (Aristotle, 1818; Ellrod, 1982; Sachs in Aristotle, 2002). Modern scholars have tended to quarantine the ancient concept of energeia from contemporary ideas about energy. But Aristotle’s term may still have value when thinking about energy’s nature. This is especially so when we take into account the ideas of Aristotle’s intellectual forebear Heraclitus, whose cosmological view was informed by three main principles: (i) that activity in nature is driven by ‘fire’ – which has been interpreted as synonymous with energy (Heisenberg, 1958), (ii) is subject to continual flux or motion, and (iii) is structured by antagonism or tension and (Kahn, 1989; Sachs in Aristotle, 2002).
We now understand there to be two main forms of energy: kinetic and potential. Kinetic energy is possessed by objects due to their motion, while potential energy is possessed by objects due to their relative position or configuration. All other forms of energy, such as thermal, electromagnetic, solar, chemical, gravitational, atomic, and so on are in themselves forms of either kinetic or potential energy (Duncan, 2002; Smil, 2008). Much can be said about kinetic and potential energy, including the fact that they are causally efficacious, that is, they cause real change and activity in the material world7. But I want to draw attention here to the fact that they are both manifestations of difference. Kinetic energy is difference as motion or change; potential energy is difference as tension or antagonism. Neither kinetic nor potential energy inhere absolutely in objects but are relational properties; motion or change occurs relative to a frame of reference, and tension or antagonism occurs between one object, or force, and another. The concept of difference then is of utmost importance when considering the nature of energy and the related properties of force and work8.
Rest in Link.
www.frontiersin.org/articles/10.3389/fpsyg.2018.02091/full
To explain consciousness as a physical process we must acknowledge the role of energy in the brain. Energetic activity is fundamental to all physical processes and causally drives biological behavior. Recent neuroscientific evidence can be interpreted in a way that suggests consciousness is a product of the organization of energetic activity in the brain. The nature of energy itself, though, remains largely mysterious, and we do not fully understand how it contributes to brain function or consciousness. According to the principle outlined here, energy, along with forces and work, can be described as actualized differences of motion and tension. By observing physical systems, we can infer there is something it is like to undergo actualized difference from the intrinsic perspective of the system. Consciousness occurs because there is something it is like, intrinsically, to undergo a certain organization of actualized differences in the brain.
Introduction
“If mental processes are indeed physical processes, then there is something it is like, intrinsically, to undergo certain physical processes. What it is for such a thing to be the case remains a mystery.”
(Nagel, 1974)
The philosopher Thomas Nagel summarized one of our greatest intellectual challenges: how to explain mental processes as physical processes. The aim of this paper is to outline a principle according to which consciousness could be explained as a physical process caused by the organization of energy in the brain1.
Energy is fundamentally important in all physical processes (Lotka, 1922; Schrödinger, 1944; Heisenberg, 1958; Boltzmann, 1886). As the biophysicist Harold Morowitz (1979) put it: “the flow of energy through a system acts to organize that system.” Light, chemical reactions, electricity, mechanical work, heat, and life itself can all be described in terms of energetic activity (Chaisson, 2001; Morowitz and Smith, 2007; Smil, 2008) as can metabolic processes in the body and brain (Magistretti, 2008; Perez Velazquez, 2009). It is surprising, therefore, that energy receives relatively little attention in neuroscientific and psychological studies of consciousness. Leading scientific theories of consciousness do not reference it (Crick and Koch, 2003; Edelman et al., 2011; Dehaene, 2014; Oizumi et al., 2014), assign it only a marginal role (Hameroff and Penrose, 2014), or treat it as an information-theoretical quantity (Friston, 2013; Riehl et al., 2017). If it is discussed, it is either as a substrate underpinning higher level emergent dynamics (Deacon, 2013) or as powering neural information processing (Sterling and Laughlin, 2017).
This lack of attention is all the more surprising given that some of the pioneers of neurobiology, psychology, and physiology found a central place for energy in their theories, including Hermann von Helmholtz (in Cahan, 1995), Gustav Fechner (1905), Sigmund Freud (Gay, 1988), William James (James, 1907), and Charles Sherrington (1940)2. There are, however, signs that attention is turning again to energetic or thermodynamic-related theories of consciousness in various branches of science (Deacon, 2013; Collell and Fauquet, 2015; Annila, 2016; Street, 2016; Tozzi et al., 2016; Marchetti, 2018) and in philosophy of mind (Strawson, 2008, 2017).
The present paper builds on this work by proposing that energy, and the related properties of force and work, can be described as actualized differences of motion and tension, and that – in Nagel’s phrase – ‘there is something it is like, intrinsically, to undergo’ actualized differences. Recent neuroscientific evidence suggests that consciousness is a product of the way energetic activity is organized in the brain. Following this evidence, I propose that we experience consciousness because there is something it is like, intrinsically, to undergo a certain organization of actualized differences in the brain.
Several researchers have tackled the problem of consciousness by treating the brain in principle as a neural information processor (e.g., Tononi et al., 2016; Dehaene et al., 2017; Ruffini, 2017). I will argue that the governing principle of the brain at the neural level is not information processing but energy processing. The information-theoretic approach to measuring and modeling brain activity, however, can usefully complement the energetic approach outlined here.
Consciousness and Energy in the Brain
We do not fully understand the biological function of energy in the brain or how it relates to the presence of consciousness in the person3. Given that the human brain accounts for only 2% of the body’s mass it demands a large portion of the body’s total energy budget, some 20% (Laughlin, 2001; Magistretti and Allaman, 2013). Most of this energy is derived from the oxidization of glucose supplied to the cerebral tissue through the blood. Roy and Sherrington were the first to propose a direct correspondence between changes in cerebral blood flow and functional activity (Roy and Sherrington, 1890). Many features of human brain anatomy, such as the number of blood vessels per unit of space, the lengths of neural connections, the width of axons, and even the ratio of brain to stomach size are thought to be determined by the high metabolic demands associated with complex cognitive processing (Allen, 2009).
For many neuroscientists, the main function of energy in the brain is to fuel neural signaling and information processing (Magistretti, 2013); energy supply is seen as a constraint on the design and operation of the brain’s computational architecture (Laughlin, 2001; Hall et al., 2012; Sterling and Laughlin, 2017). It has been calculated, for example, that the rate of energy supply available to the human brain places an upper ‘speed limit’ on neural processing of about 1 kHz (Attwell and Gibb, 2005). And Schölvinck et al. (2008) estimated that conscious perception of sensory stimuli increases energy consumption in primate brains by less that 6% compared to energy consumption in the absence of conscious perception4. They attribute this relatively small change to an energy efficient “design strategy” of the brain in which decreases in neural activity play a functional role in information processing as well as increases. Energy, on these accounts, plays no direct role in higher mental processes, like consciousness.
Robert Shulman and colleagues have argued there is a direct connection between energy in the brain and consciousness (Shulman et al., 2009; Shulman, 2013). By studying the progressive loss of behavioral response to external stimulus from wakefulness to deep anesthesia, they found a corresponding reduction and localization of cerebral metabolism (a marker of energy consumption). Therefore, they argue, high global metabolism is necessary for consciousness. However, they are also clear that high global metabolic rates are not sufficient as patients with locked-in-syndrome and those who suffer from some forms of epileptic seizure can register high levels of global brain metabolism without exhibiting the observable behavior that we expect from a conscious person (Shulman, 2013; Bazzigaluppi et al., 2017). Shulman’s thesis has been challenged on several grounds (Seth, 2014). For example, it has been pointed out that behavioral responsiveness may be inadequate as a measure of sentience given that vestiges of consciousness have been detected in people diagnosed as being in a vegetative state with a low cerebral metabolism (Owen et al., 2006). Moreover, some patients who recover from a vegetative state to regain consciousness do so despite having substantially reduced cerebral metabolism compared with normal controls (Laureys et al., 1999; Chatelle et al., 2011).
In recent years there has been a growing interest in intrinsic brain activity (Clarke and Sokoloff, 1999; Raichle, 2011). This background or spontaneous activity occurs in the resting awake state in the absence of external stimulation or directed attention, and its energy demands can greatly exceed those of localized activation due to task performance or attention. The discovery of this so-called ‘dark energy’ in the brain (Raichle, 2010) was greeted with some surprise in the neuroscience community and remains controversial (Morcom and Fletcher, 2007). Work on intrinsic activity led to the identification of a ‘default mode network’ in the brain, an extended set of interconnected regions that uses high levels of energy when a person is in a non-attentive state. Energy use drops significantly in this network when a more cognitively demanding task, such as paying attention to a stimulus, is performed (Shulman et al., 1997; Raichle et al., 2001). Vanhaudenhuyse et al. (2009) reported that connectivity within the default mode network in patients with severe brain-damage deteriorates in proportion to the degree of conscious impairment, suggesting it plays an important role in sustaining consciousness.
Meanwhile, it is somewhat surprising to find that energy use during non-rapid eye movement sleep remains at ∼85% of that in the waking state, while during rapid eye movement sleep it can be as high as in the waking state (Dinuzzo and Nedergaard, 2017). At the same time, consciousness can be minimally sustained with energy use at only 42% of the level that occurs in healthy conscious individuals, suggesting that much cerebral metabolic activity in normal waking states does not directly contribute to consciousness (Stender et al., 2016). Many anesthetic agents are thought to obliterate consciousness because they reduce the global rate of cerebral metabolism (Hudetz, 2012). Administering ketamine, on the other hand, increases brain metabolism yet can still lead to loss of responsiveness (Pai and Heining, 2007). Overall, it seems we find no clear correlation between the total amount of energy used by the brain, or the location where the energy is used, and the level of consciousness detectable in the person.
Consciousness and the Organization of Energetic Processing in the Brain
An alternative, or perhaps complementary, way to think about this issue is in terms of how the energetic activity in the brain is organized rather than its global level or localization. Indeed, this has implicitly been the focus of recent research that aims to provide quantitative measures of consciousness levels. In one study, researchers used transcranial magnetic stimulation (TMS) to send a magnetic pulse through the brains of healthy controls and patients with various states of impaired consciousness (Casali et al., 2013). By measuring how the pulse perturbed the cortex the researchers were able to determine the relative complexity and extent of the pathways through which the pulse propagated and correlate these to levels of consciousness. The researchers calculated a perturbation-complexity index (PCI) that quantified the levels of consciousness present in each person they studied. This method was further validated as a reliable objective measure of levels of consciousness by Casarotto et al. (2016).
The PCI was calculated using data from electroencephalographic (EEG) measurements of the cerebral perturbation following the TMS. Images from the EEG were filtered into binary data that was then analyzed using a Lempel–Ziv algorithm, a commonly used information-theoretical technique in which complexity is measured as a function of data string compressibility, with more complex data strings being less compressible (Ziv and Lempel, 1977; Aboy et al., 2006). Other researchers have developed similar information-theoretical methods for quantifying the complexity of brain activity and levels of consciousness. King et al. (2013) analyzed data from 181 EEG recordings of patients who were diagnosed with varying states of impaired consciousness and applied a measure of weighted symbolic mutual information (wSMI) that sharply distinguished between patients in vegetative state, minimally conscious state, and conscious state.
Although information theoretic tools were being used to analyze and interpret the data in these studies we should note that what was actually being detected by the experimental procedures was not information per se but the organization of energetic activity or processing in the brain. Energetic processing – the processes by which the brain regulates the flow of energy through its structures – is routinely detected at varying degrees of spatial and temporal resolution, either directly or indirectly, by neuroimaging techniques such as positron emission tomography (PET), functional magnetic resonance image (fMRI), and EEG (Niedermeyer and Lopes da Silva, 1987; Bailey et al., 2005; Shulman, 2013). Referring again to the study by Casali et al. (2013), the perturbations from which the PCI was calculated were generated by a pulse of magnetic energy from the TMS and were imaged with EEG that measures electrical voltage differences, that is, fluctuations in energetic potentials between clusters of neurons in the cortex (Niedermeyer and Lopes da Silva, 1987; Hu et al., 2009; Koponen et al., 2015). The PCI and wSMI can therefore be interpreted as measures of the complexity or organization of energetic processing in the brain during the experimental procedures.
Subsequent research has directly investigated the connection between brain metabolism (how the brain regulates energy conversion), brain organization, and levels of consciousness by combining EEG measures with PET, a more specific measure of cerebral metabolism. Chennu et al. (2017) collected data from 104 patients in varying states of conscious impairment using both techniques. By analyzing this data, they determined a metric that discriminated levels of consciousness to a high degree of accuracy. This study built on previous work by Demertzi et al. (2015) that used fMRI to correlate a measure of intrinsic functional connectivity in the brain with levels of consciousness. The PCI method has been further validated by a study combining EEG and 18F-fluorodeoxyglucose (FDG)-PET (Bodart et al., 2017), so reinforcing the link between levels of consciousness and the organization of metabolic activity in the brain.
Current brain imaging methods do not strictly speaking detect information processing5. They do, however, detect changes associated with increases in energy consumption (via fMRI and PET) and fluctuations in electrical potential energy (via EEG), both of which reliably correlate with changes in mental function and behavior. On the basis of what we can observe, the brain operates according to the principle of energetic processing. The evidence discussed above suggests levels of consciousness are determined by the organization of energy processing in the brain rather than on its global level or localization; wakeful conscious states are associated with more complex organization. To understand why this might be we need to consider the concept of energy in more depth.
Energy
The concept of energy that we are familiar with today emerged only slowly from its beginnings in the late eighteenth century. It developed through the study of thermodynamics in the nineteenth century, and then found its place at the center of theories of relativity, quantum mechanics, and cosmology in the twentieth (Coopersmith, 2010). In colloquial usage energy refers to ideas of vigor, vitality, power, activity, and zest. In scientific usage, however, energy is defined as the ability of a system to do work6. Work is defined as the transfer of energy involved in moving an object over a distance by an external force, at least part of which is applied in the direction of the displacement (Duncan, 2002). Scientists and engineers often refer to energy as an abstract property: “Energy is a mathematical abstraction that has no existence apart from its functional relationship to other variables” (Abbott and Van Ness, 1972; Rose, 1986). It is a property that can be converted from one form to another, and in an isolated system the total quantity is conserved (Smil, 2008).
Despite the enormous amount of interest in the physics of energy and its central importance in so many branches of science, its nature remains in many ways mysterious (Feynman, 1963; Smil, 2008; Coopersmith, 2010) and it has been the subject of relatively little philosophical interrogation (Coelho, 2009). Treating energy as an abstract accounting quantity is perfectly satisfactory for many scientific purposes, where there is little reason to question its nature. But if energetic activity plays a significant role in consciousness, as the evidence cited above suggests it might, then its nature deserves closer scrutiny.
The concept of energy in the European intellectual tradition can be traced back to Aristotle who used but never precisely defined the term energeia (ενwww.frontiersin.orgρwww.frontiersin.orgεια) to convey the ideas of action, activity, actuality, being at work, and acting purposefully (Sachs in Aristotle, 2002). Scholars have long debated the best way to translate energeia from ancient Greek. The word ‘energy’ itself has been used, as have ‘activity’ and ‘actuality,’ but ‘being-at-work’ is currently favored, partly due to energeia’s roots in ergon, the ancient Greek for work (Aristotle, 1818; Ellrod, 1982; Sachs in Aristotle, 2002). Modern scholars have tended to quarantine the ancient concept of energeia from contemporary ideas about energy. But Aristotle’s term may still have value when thinking about energy’s nature. This is especially so when we take into account the ideas of Aristotle’s intellectual forebear Heraclitus, whose cosmological view was informed by three main principles: (i) that activity in nature is driven by ‘fire’ – which has been interpreted as synonymous with energy (Heisenberg, 1958), (ii) is subject to continual flux or motion, and (iii) is structured by antagonism or tension and (Kahn, 1989; Sachs in Aristotle, 2002).
We now understand there to be two main forms of energy: kinetic and potential. Kinetic energy is possessed by objects due to their motion, while potential energy is possessed by objects due to their relative position or configuration. All other forms of energy, such as thermal, electromagnetic, solar, chemical, gravitational, atomic, and so on are in themselves forms of either kinetic or potential energy (Duncan, 2002; Smil, 2008). Much can be said about kinetic and potential energy, including the fact that they are causally efficacious, that is, they cause real change and activity in the material world7. But I want to draw attention here to the fact that they are both manifestations of difference. Kinetic energy is difference as motion or change; potential energy is difference as tension or antagonism. Neither kinetic nor potential energy inhere absolutely in objects but are relational properties; motion or change occurs relative to a frame of reference, and tension or antagonism occurs between one object, or force, and another. The concept of difference then is of utmost importance when considering the nature of energy and the related properties of force and work8.
Rest in Link.