In the Light of Evolution Volume VII: The Human Mental Machinery (2014) / Chapter Skim
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3 Evolution of Consciousness: Phylogeny, Ontogeny, and Emergence from General Anesthesia--George A. Mashour and Michael T. Alkire
3 Evolution of Consciousness: Phylogeny, Ontogeny, and Emergence from General Anesthesia--George A. Mashour and Michael T. Alkire
Pages 37-56
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From page 37... ...
We propose that the stepwise emergence from general anesthesia can serve as a reproducible model to study the evolution of consciousness across various species and use current data from anesthesiology to shed light on the phylogeny of consciousness. Ultimately, we conclude that the neurobiological structure of the vertebrate central nervous system is evo lutionarily ancient and highly conserved across species and that the basic neurophysiologic mechanisms supporting consciousness in humans are found at the earliest points of vertebrate brain evolution.
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From page 38... ...
. Phenomenal consciousness relates solely to subjective experience, whereas access consciousness includes (among other processes)
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From page 39... ...
access Phenomenal consciousness is subjective experience consciousness itself, whereas access consciousness is that which is available to other cognitive processes (such as working memory or verbal report)
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From page 40... ...
In this view, the midline brain structures of brainstem and midbrain are thought to be important for keeping the cortex in an aroused or awake state, whereas the cortical regions are thought to serve as specific cognitive modules contributing to the contents of conscious experience. The idea that certain brain regions are more important than others for generating the contents of consciousness is further supported by a number of basic neurological facts.
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From page 41... ...
. The lateral frontoparietal network plays a role in mediating consciousness of the environment, whereas the medial frontoparietal network plays a role in mediating internal conscious states such as dreaming and internally directed attention (Boly et al., 2007; Denton et al., 2009)
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From page 42... ...
Ancient brain structure evolution theory of Scala Naturae showing brain development proceeding from simple to more complicated with the addition of new brain regions as evolution progressed. This erroneous view is compared with a modern understanding of brain structure evolution that reveals a basic common structure evolved in the vertebrate brain and various regions expanded to accommodate each specific animal's needs.
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From page 43... ...
Put another way, years before behaviorism dominated neuroscience, Darwin saw how commonalities in emotional expression across species likely reflected the occurrence of similar underlying states of mind that only made sense within a theory of evolution. Modern study into the emotional lives of animals now reveals how fundamentally similar the brain structures are that support affective reactions in animals and humans (Panksepp, 2011)
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From page 44... ...
Creatures that could meet their basic homeostatic needs are the ones that survived; those that did not suffered extinction. The brain structures needed for generating arousal and primitive emotional responses are generally located in the brainstem, midbrain, and limbic system and are as old as the vertebrate radiation itself (Jing et al., 2009)
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From page 45... ...
This emotional arousal machinery underlies essentially all behavioral choices in the vertebrate brain. CONSCIOUSNESS IN NONHUMAN SPECIES If consciousness evolved in conjunction with cephalad development of the central nervous system, then its emergence should, in principle, be identifiable at a discrete point on the tree of evolution.
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From page 46... ...
To identify the origin of sentience along an evolutionary timeline, it is beneficial to consider a common element that might link consciousness across species, rather than focusing on the ostensibly unique qualities of human experience such as self-reflection. Furthermore, this common element should likely relate to a goal-directed behavior or response pattern that confers a survival advantage in a given environment.
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From page 47... ...
WHAT IS THE NEURAL "CORE" OF CONSCIOUSNESS? To identify which aspects of the mental machinery should be the focus of evolutionary consideration for consciousness, we need to identify the neural correlates of the most primitive core of human consciousness.
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From page 48... ...
Thus, the core of human consciousness appears to be associated primarily with phylogenetically ancient structures mediating arousal and activated by primitive emotions (Liotti et al., 2001; Denton et al., 2009) , in conjunction with limited connectivity patterns in frontal–parietal networks (Merker, 2007; Brusseau, 2008)
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From page 49... ...
General anesthesia represents a way of turning back the evolutionary clock of cognitive function in humans and -- depending on the "depth" and length of anesthetic exposure -- allows investigators to observe the return of neural function in a way that could recapitulate phylogeny. Although not without difficulties (including the contamination of access consciousness, because language is involved in assessing return of consciousness after anesthesia)
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From page 50... ...
WHEN DOES CONSCIOUSNESS OF THE WORLD ARISE? The recent experiments with general anesthesia in humans suggest that phylogenetically ancient structures in the brainstem and diencephalon -- with only limited neocortical involvement -- are sufficient to support primitive consciousness.
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From page 51... ...
As shown in Fig. 3.2, the neural correlates for awareness of subjective arousal induced by viewing of emotional stimuli involve the same midbrain arousal structures seen with activation of primordial emotions (Hayama et al., 2012)
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From page 52... ...
On seeing themselves in the mirror, the marked chimpanzees -- but not the marked monkeys -- exhibited mark-directed responses by spending time investigating the area of the mark and examining their fingers after touching the mark. The findings led Gallup to conclude "insofar as self-recognition of one's mirror image implies a concept of self, these data would seem to qualify as the first experimental demonstration of a self-concept in a subhuman form." Regarding the difference between chimpanzee and monkey, he further concluded, "Our data suggest that we may have found a qualitative psychological difference among primates, and that the capacity for selfrecognition may not extend below man and the great apes." The distinction among primates suggests that the qualitative nature of the conscious experience varies greatly across species and the introspective nature of human consciousness may be evolutionarily quite rare.
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From page 53... ...
. The cognitive abilities of various birds seem to correlate with the relative size of the analogous avian prefrontal cortex.
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From page 54... ...
However, what accounts for the richness of human experience in contrast to those of early mammals or birds? Drawing on the integrated information theory of consciousness, the evolution of more complex brain networks capable of synthesizing the outputs of more functionally diverse modules would result in a higher capacity for consciousness.
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From page 55... ...
. Indeed, a recent neural mass model based on structural connectivity data from diffusion tensor imaging in humans predicts an information flow from the frontal to the posterior parietal cortex (Stam and van Straaten, 2012a)
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From page 56... ...
Using recent data from general anesthesia in humans, we suggest that the arousal centers in the brainstem and diencephalon -- in conjunction with even limited neocortical connectivity and recurrent processing -- can result in primitive phenomenal consciousness. By "reverse engineering," we postulate that early mammals and birds possessing these structures (or their equivalents)
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