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Evolution of consciousness: Phylogeny, ontogeny, and emergence from general anesthesia


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Are animals conscious? If so, when did consciousness evolve? We address these long-standing and essential questions using a modern neuroscientific approach that draws on diverse fields such as consciousness studies, evolutionary neurobiology, animal psychology, and anesthesiology. 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 evolutionarily 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. Thus, in agreement with Darwin's insight and the recent "Cambridge Declaration on Consciousness in Non-Human Animals," a review of modern scientific data suggests that the differences between species in terms of the ability to experience the world is one of degree and not kind.
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Evolution of consciousness: Phylogeny, ontogeny,
and emergence from general anesthesia
George A. Mashour
and Michael T. Alkire
Departments of Anesthesiology and Neurosurgery, Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, MI 48109; and
Veterans Administration Long Beach Healthcare System, Department of Anesthesiology and Perioperative Care, Center for the Neurobiology of Learning
and Memory, University of California, Irvine, CA 92697
Edited by Francisco J. Ayala, University of California, Irvine, CA, and approved April 9, 2013 (received for review February 11, 2013)
Are animals conscious? If so, when did consciousness evolve? We
address these long-standing and essential questions using a modern
neuroscientic approach that draws on diverse elds such as con-
sciousness studies, evolutionary neurobiology, animal psychology,
and anesthesiology. 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 evolutionarily ancient and highly
conserved across species and that the basic neurophysiologic mecha-
nisms supporting consciousness in humans are found at the earliest
points of vertebrate brain evolution. Thus, in agreement with Darwins
insight and the recent Cambridge Declaration on Consciousness in
Non-Human Animals,a review of modern scientic data suggests
that the differences between species in terms of the ability to experi-
ence the world is one of degree and not kind.
Evolutionary biology forms a cornerstone of the life sciences and
thus the neurosciences, yet the emergence of consciousness
during the timeline of evolution remains opaque. As the theory of
evolution began to eclipse both religious explanations and Enlight-
enment doctrines regarding the singularity of human consciousness,
it became clear that consciousness must have a point of emergence
duringevolution andthat point likelyoccurred before Homo sapiens.
How,Darwin questioned, does consciousness commence?His
post-Beagle research on this question evidently caused him violent
headaches. One such headache can be expressed as the 20th century
philosophical distinction of phenomenal consciousness and access
consciousness (1). Phenomenal consciousness relates solely to sub-
jective experience, whereas access consciousness includes (among
other processes) the ability to report such experiences verbally
(otherdistinctions related to consciousness can befound in Table 1).
Thus, thescientist looking for objectiveindices of subjective events is
primarily limited to humans manifesting access consciousness, an
obstacle in studying the evolution of consciousness antecedent to
our species. We could, however, take solace in the dictum that on-
togeny recapitulates phylogeny and search for clues in developing
humans. Unfortunately, Haeckels theory of recapitulation is not
scientically sound and, even if applicable in this case, we would still
be constrained by the high probability that babies develop phe-
nomenal consciousness before access consciousness. To overcome
the limitations in identifying the birth of consciousness, we need
a reproducible experimental model in which (i) consciousness
emerges from unconsciousness at a discrete and measurable point,
(ii) phenomenal consciousness and access consciousness are closely
juxtaposed or collapsed, and (iii) assessment of neural structure and
function is possible. In this article, we consider top-down and bot-
tom-up approaches to consciousness, nonhumanconsciousness, and
the emergence of consciousness from general anesthesia as a model
for the evolution of subjectivity.
Top-Down and Bottom-Up Approaches to Consciousness
To locate the birth of consciousness on the evolutionary time-
line, it will be benecial to consider the basic neural machinery
that is thought to be involved in human consciousness (28). The
distinction between phenomenal and access consciousness was
noted, but phenomenal consciousness itself reects the disso-
ciable neurobiological processes of awareness and arousal (913)
(Table 1). Awareness refers to the content of consciousness (red
apple vs. blue sky), whereas arousal refers to brain activation and
level-of-consciousness (alert vs. drowsy vs. asleep vs. anesthetized).
A number of current theories about consciousness propose that
the cortex is the primary site containing the neural correlates of
awareness (1419), whereas midline subcortical brain structures
provide ascending arousal inuences to the cortex (15, 17, 19).
Thus, we can explore both top-down and bottom-up approaches
to consciousness.
Top-Down Approach. Seth et al. (14) propose three main physio-
logical reasons supporting the importance of the neocortex to
the process of consciousness. First, the electroencephalogram
of virtually all mammals and birds in the awake state is charac-
terized by desynchronized, high-frequency, and low-amplitude
activity. This pattern changes to one of low-frequency, high-
amplitude activity during depressed levels of consciousness such
as nonrapid eye movement (NREM) sleep, minimally conscious
states, and anesthesia. Thus, a state-dependent change in the
electrical ring properties of the neurons across the neocortex
varies with the level of arousal and strongly supports the idea
that neuronal activity in the brain (and particularly in the neo-
cortex) is a necessary requirement for consciousness (20).
Second, consciousness appears to be linked more specically
with neural activity in the thalamocortical system. 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 specic
cognitive modules contributing to the contents of conscious ex-
perience. The idea that certain brain regions are more important
than others for generating the contents of consciousness is fur-
ther supported by a number of basic neurological facts. For in-
stance, a person could suffer the loss of the cerebellum or large
bilateral portions of the medial temporal lobes, including
amygdala and hippocampus complex, and would not become
unconscious. However, focal damage to specic areas of cortical
tissue will change the contents of a persons consciousness in
a way that matches the loss of function associated with the
specic area damaged. Cortical lesions can thus result in such
specic impairments of consciousness that one may no longer be
able to speak, perceive color, or identify parts of themselves as
their own (21). Damage to lower midline brain structures, on the
This paper results from the Arthur M. Sackler Colloquium of the National Academy of
Sciences, In the Light of Evolution VII: The Human Mental Machinery,held January
1012, 2013, at the Arnold and Mabel Beckman Center of the National Academies of
Sciences and Engineering in Irvine, CA. The complete program and audio les of most
presentations are available on the NAS Web site at
Author contributions: G.A.M. and M.T.A. wrote the paper.
The authors declare no conict of interest.
This article is a PNAS Direct Submission.
To whom correspondence should be addressed. E-mail: PNAS
June 18, 2013
vol. 110
suppl. 2
other hand, will likely alter the level of consciousness (i.e., arousal)
without necessarily changing its contents.
Thalamocortical oscillations have been posited to be of critical
importance to consciousness because they help integrate func-
tionally diverse and spatially distinct cognitive modules in the
cortex (22, 23). The interplay of segregation and integration is
a fundamental focus of the integrated information theory of con-
sciousness (8, 24). The capacity of the thalamocortical system to
achieve both integration and differentiation is reected in higher
levels of Phi, a proposed metric for consciousness (8). Phi reects
the amount of information generated by an integrated system
beyond the information contained within the components of the
system. In principle, this measure captures the emergent property
of the system (consciousness) that cannot be causally reduced to
individual subsystems (particular brain regions). Phi is predicted to
decrease during sleep and seizures; preliminary evidence suggests
it also decreases during anesthesia (25), possibly due to impaired
long-range coupling of neural spike activity (26). Although the
integrated information theory of consciousness has yet to be de-
nitively demonstrated, it is a guiding paradigm that can inform
the evolution of consciousness from the network perspective.
Creatures with brain network systems that are capable of gener-
ating high values of Phi are more likely to be conscious (27).
Third, widespread brain activity appears correlated with con-
scious activity. Sensory input spreads quickly from sensory cortex
to parietal, temporal, and prefrontal areas (28). This spread of
cortical activity is also associated with recurrent local feedback
occurring along the way, followed shortly thereafter by long-
range feedback from anterior to posterior structures (29). These
long-range connections are thought to be important for the ex-
periential aspects of consciousness (i.e., awareness) (30) and
appear to be preferentially suppressed during general anesthesia
(26, 31). In particular, there is strong evidence that networks
across the frontal and parietal cortices are associated with
awareness across multiple sensory modalities (3234). The lat-
eral frontoparietal network plays a role in mediating conscious-
ness of the environment, whereas the medial frontoparietal
network plays a role in mediating internal conscious states such
as dreaming and internally directed attention (35, 36). It is be-
coming increasingly clear that the directionality of corticocortical
network communication is relevant to conscious processing. In-
formation processing from the caudal to rostral direction (feed-
forward) is associated with sensory processing that can occur in
the absence of consciousness (e.g., general anesthesia, priming)
(37, 38). In contrast, information processing in the rostral-to-
caudal direction (feedback or cortical reafference) is thought to
be associated with experience itself and is preferentially inhibited
by general anesthetics (3840).
The neocortical view of consciousness originates, in part, from
early morphologic examination of brain differences across species
that suggested the capacities of consciousness increased as brains
evolved from more primitive reptilian organization, to mammalian
(or, with a limbic system, paleomammalian), and then neo-
mammalian organization, characterized by an intricately folded
neocortex. This conceptualization of brain evolution occurring in
stages during which more advancedbrainsalong with their ex-
panded behavioral repertoirewere built on the structure of earlier
forms was popularized by Maclean as the triune brain(41). Im-
portantly, this view of brain evolution is now largely considered er-
roneous (42, 43). It did offer an easy conceptualization for relating
brain structure with function and suggested evolutionary time points
for when various behaviors would have emerged. Newer ndings,
however, strongly refute the model of a triune brain, especially the
concept of a later developing neocortex (Fig. 1) (42). As it turns out,
a precursor of the neocortex was actually present in the earliest
evolving vertebrates, a claim based on some aspects of connectivity
and homology of early transcription factor expression (44). The basic
structural pattern of a brainstem, midbrain, and forebrain did not
need to be completely reinvented as each new species emerged.
Rather, as various ecological niches were exploited by various crea-
tures, those brain regions best suited for enhancing survival in the
local environment were emphasized for further development (42).
Bottom-Up Approach. Since the discovery of the ascending re-
ticular activating system by Moruzzi and Magoun in the late
1940s (45), the fundamental and permissive role for arousal in
generating conscious states has been well established. It is now
Table 1. Denitions relevant to consciousness
Terms Explanation
Easy vs. hard problem of consciousness This distinction was drawn by philosopher David Chalmers. Easy
problems of consciousness (which are easy in principle only) include
understanding the neural basis of feature detection, integration,
verbal report, etc. The hard problem is the problem of experience;
even if we understand everything about neural function, it is not
clear how that would explain subjectivity.
Awareness Cognitive neuroscientists and philosophers use the term awareness
to mean only subjective experience. In clinical anesthesiology, the
term awareness is (inaccurately) used to include both consciousness
and explicit episodic memory.
Wakefulness vs. awareness Wakefulness refers to brain arousal, which can be manifest by
sleepwake cycles and can occur even in pathologic conditions of
unconsciousness such as vegetative states. Thus, being awake is
dissociable from being aware.
Phenomenal vs. access consciousness Phenomenal consciousness is subjective experience itself, whereas access
consciousness is that which is available to other cognitive processes
(such as working memory or verbal report).
External vs. Internal consciousness External consciousness is the experience of environmental stimuli
(such as the sound of an orchestra), whereas internal consciousness is
an endogenous experience (such as a dream state).
Consciousness vs. responsiveness An individual may fully experience a stimulus (such as the command
Open your eyes!) but not be able to respond (as when a patient is
paralyzed but conscious during surgery).
Levels of consciousness vs. contents of consciousness Levels of consciousness include distinctions such as alert vs. drowsy vs.
anesthetized, whereas the contents of consciousness refer to particular
phenomenal aspects such as a red rose vs. a blue ball.
| Mashour and Alkire
clear how a number of specic nuclei and specic cell types within
the brainstem, midbrain, basal forebrain, and diencephalon send
long-range axons throughout the cortex to enhance arousal and
generate a neurochemical environment in the cortex that is ca-
pable of supporting consciousness (11). The role of arousal in
regulating overall levels of consciousness is clearly established in
connection with depressed levels of consciousness as during sleep
or coma (46). How arousal machinery interacts with conscious-
ness during more subtle cognitive and behavioral manipulations is
the subject of much current research (4749). However, through
the study of arousal as it relates to emotion (50, 51), another link
is made that puts some of Darwins later investigations into
a more modern light.
Darwin spent the later years of his career investigating the
similarities and differences associated with emotional expression
in man and animals (52). He reasoned that if animals show
emotion through behavioral expression, and man is an animal,
then the behavioral expression of emotion in man must share
a similar neurobiologic evolution with the other animals capable
of expressing similar emotions. Put another way, years before
behaviorism dominated neuroscience, Darwin saw how com-
monalities in emotional expression across species likely reected
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 sim-
ilar the brain structures are that support affective reactions in
animals and humans (53).
Consciousness may not have emerged from the need to make
an internal representation of the outside world, but rather as an
extension of very basic primitive or primordial emotional inu-
ences. Such emotional inuences would generate an arousal
response in an organism and prepare its brain for action. This
hypothesis is well elaborated by Denton in his book on primor-
dial emotions (6). It posits that the most basic instincts, such
as thirst, hunger for air, hunger for salt and food, and the
desire for sex are the dening starting points for evolving
a conscious brain (36). This idea holds within it the concept of
intention, desire, and action selection, where the basic intention
of a movement is in the service of fullling a desire. As noted by
Darwin (52), So strongly are our intentions and movements
associated together, that if we eagerly wish an object to move in
any direction, we can hardly avoid moving our bodies in the same
direction, although we may be perfectly aware that this can have
no inuence.
The basic behavior of an organism is driven by a fundamental
physiologic need to maintain homeostasis. Those cells and
systems used for monitoring and maintaining the internal milieu
are referred to as interoceptors (6). The basic behaviors driving
homeostasis are evident as far back as the rst multicellular
organisms that needed a vascular system to provide nutrients
to those cells no longer exposed directly to the environment.
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 (54).
Recent work on the lamprey, a jawless sh whose common
ancestor forms the basis for all vertebrates more than 500 million
years ago, has revealed just how ancient the neuroanatomy and
neurochemistry needed for action selection is. Findings reveal
that the lampreys behavioral motor output system shows similar
complexity to higher-level vertebrates who are capable of regu-
lating behavior by both direct and indirect motor output pathways
from the basal ganglia (55). In other words, the lamprey is capable
of both selecting a motor output to perform and at the same time
inhibiting the performance of other possible outputs. Thus, they
are capable of making a choice depending on the situation with
which they are confronted. This reduction of uncertainty(a
classic denition of information) through action selection may be
the precursor to the highly informative states of consciousness
characteristic of humans. We address the relationship of motoric
behavior and consciousness in the next section.
More complex neocortical abilities offered a survival advan-
tage to more complex brains by giving organisms a larger grasp of
their surroundings, but these systems developed over time and
used sensory information from the environment or exteroreceptors
(6). Denton illustrates his point with the example of a dehydrated
frog placed next to a water source in the sun. The frog has only
a limited capacity in its visual system and when placed next to
a source of water it will usually die without moving, unless it
stumbles on the water by accident. If, by chance, the frog nds the
water, it will drink, which suggests functioning interoreceptors. In
contrast, the more highly evolved visual system of the lizard allows
that creature to see the water and immediately drink, suggesting
that its more evolved brain more successfully couples its extero-
receptor-mediated perceptions with its interoreceptor-mediated
needs. This coupling of an internally based need system with an
externally based situational awareness system is likely the foun-
dation for the emergence of consciousness, and it closely corre-
sponds to the mental machinery seen in humans for generating
awareness and arousal.
The brainstem arousal centers are, for the most part, juxta-
posed with the sensory motor inputs and outputs of the cranial
nerves that supply the head and neck with its ability to orient
a creature to its environment and provide a stable platform for
sensing its surroundings. The motor output of the cranial nerves
is fundamentally linked with the expression of emotion in es-
sentially all vertebrates, and this likely emanates from the oldest
of the predatorprey relationships. In essence, an open mouth
signies a meal for the predator, and if the hunt is successful, it
would likely be associated with internal sensations of goal/task
completion that would serve to fulll a basic need for food in the
predator. This goal completion/desire fulllment would likely
have positive reinforcing value for an organism and might easily
be hypothesized to lead to internal states comparable to a sense
of pleasure (53). For the prey, an open mouth heading toward it
would certainly be cause for alarm, prompting an immediate
escape response that, if successful, might be associated with an
internal state of heightened arousal and fear (53). Thus, the most
basic emotions and arousal states are associated with internal
feedback networks that serve to guide an organisms behavior
toward its best possible situational outcome. This emotional
arousal machinery underlies essentially all behavioral choices in
the vertebrate brain.
Fig. 1. Theories of brain evolution. 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
specic animals needs. Modied from (42) with permission from Elsevier.
Mashour and Alkire PNAS
June 18, 2013
vol. 110
suppl. 2
Consciousness in Nonhuman Species
If consciousness evolved in conjunction with cephalad develop-
ment of the central nervous system, then its emergence should, in
principle, be identiable at a discrete point on thetree of evolution.
Darwin reasoned that the cognitive differences between species
must be one of degree and not kind. This conclusion is consistent
with the recent Cambridge declaration that occurred on July 7,
2012, at the rst annual Francis Crick memorial conference on
consciousness.A group of prominent scientists formally declared in
a document entitled the Cambridge Declaration on Conscious-
ness in Non-Human Animalsthat the neurobiological structures
needed to support consciousness are not uniquely human (56). This
declaration essentially states that the capacity for consciousness
likely emerged very early in evolutionaryterms, and those processes
that support consciousness in humans are likely characteristic of
many living creatures. In fact, according to the declaration, based
on a number of considerations from comparative brain anatomy
and current knowledge about the neurobiology of consciousness, it
would seem almost certain that some form of consciousness is
present in all mammals and could have emerged on the evolu-
tionary timeline at the branch point of amniotes.
However, long before the Cambridge declaration, some thinkers
expressed serious concerns about attributing higher levels of con-
sciousness to all life. Indeed, Rene Descartes, often considered the
philosophical father of the mindbody relationship, questioned
whether a conscious self arose in the animal kingdom. He avoided
ascribing a conscious self to a particular animal because by doing so
he recognized that he mightbe compelled to ascribe a conscious self
to all animals. This all or none approach did not reect an evolu-
tionary theory perspective, which raised the possibility of a con-
scious continuum. This continuum, however, also introduces
difculty. As pointed out by Gallup, in discussing the emergence of
consciousness in animals (57), Where do we draw the line? On the
one hand, we could decide not to draw a line. This would presume
that all living things are sentient, conscious, and mindful. While the
data are admittedly incomplete, the issue should be taken seri-
ously. Life on this planet consists of several million different spe-
cies. Most are microorganisms, plants, and insects. I doubt that
there is a paramecium, a rosebush, or a termite alive today which is
aware of its own existence or has the capacity to become the object
of its own attention.With Gallups statement, we begin to see the
need for clarity in how or why we associate certain behaviors with
subjective experience and the need for some operational de-
nitions of the consciousnessbeing studied.
To identify the origin of sentience along an evolutionary time-
line, it is benecial 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-reection.
Furthermore, this common element should likely relate to a goal-
directed behavior or response pattern that confers a survival
advantage in a given environment. In line with philosophers such
as Merleau-Ponty and neuroscientists such as Rudolfo Llinás and
György Buzsáki, we support motility (also referred to in this
context as motricity) as a strong candidate for the evolutionary
anlage of consciousness (58, 59). Consider, for example, the
unicellular paramecium, which is covered with several thousand
cilia. These cilia can serve both the function of sensing envi-
ronmental stimuli and initiating motility responses (e.g., attrac-
tion, avoidance) based on the nature of those stimuli. This
preneural example of a single structure (i.e., cilia and their co-
ordinated activity) mediating both sensation and response is in-
triguing but does not establish the primacy of motility as a kernel
of consciousness. Perhaps a more compelling case is that of the
sessile sea squirt, which possesses neural structures only tran-
siently during a larval stage (60). Neural ganglia and primordial
sensory processing allow the sea squirt to nd a suitable local
environment and underwater surface for attachment. However,
after this goal is achieved the neural tissue is digested, suggesting
a role related exclusively to movement. Although it is unlikely
that paramecia and sea squirts have phenomenal experience,
these early examples of sensation in the service of motility lead
us to start the search for the neurobiological origins of con-
sciousness in phylogenetically conserved structures.
What Is the Neural Coreof 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. The still emerging eld of consciousness
studies has been dominated in the last decade by a search for the
neural correlates of consciousness, which have been dened as
the specic and minimally adequate brain states that correspond
to states of consciousness (61). However, studies of the content
of consciousness (e.g., the awareness of a red rose placed in your
visual eld) already assume a conscious brain; thus, the neural
activity or structure identied in these paradigms correspond to a
specic content within a preexisting consciousness (62). Studying
the level of consciousness (e.g., arousal states) is also beset with
difculties. For example, the transition from a fully conscious to
unconscious state will inform us primarily of correlates required
for the full spectrum of waking human consciousness rather than
the minimal or core requirements. Furthermore, we must also
grapple with how to identify the true correlate (or substrate) of
consciousness vs. neural prerequisites or neural consequences of
consciousness (63, 64).
To address some of these difculties, a recent study explored
the neural correlates of the primitive form of consciousness that
arises during emergence from general anesthesia (65). With
anesthesia, the level of consciousness can be manipulated as an
experimental variable, and the resultant changes in brain activity
can then be determined with various neuroimaging and neuro-
physiologic techniques. Numerous studies have now examined
what happens to brain activity when consciousness is removed by
anesthesia (66, 67); however, fewer studies have investigated the
correlates of consciousness associated with its return following
a period of anesthesia (6871). In one recent study of healthy
male volunteers, positron emission tomography (PET) was used
to investigate the neural correlates of the recovery of con-
sciousness from the i.v. anesthetics propofol and dexmedeto-
midine (65). The order of the state transition is important
because the investigation of consciousness to unconsciousness
may yield a variety of nonspecic deactivations due to drug
effects that do not necessarily play a core role in consciousness.
The emergence of consciousness (as judged by the return of
a response to command) was correlated primarily with activity of
the brainstem (locus coeruleus), hypothalamus, thalamus, and
anterior cingulate (medial prefrontal area). Surprisingly, there
was limited neocortical involvement that correlated with this
primitive form of consciousness. Frontalparietal connectivity
appeared to be the key cortical response, which has been con-
rmed by studies of consciousness and anesthesia using electro-
encephalography (70). Similar ndings were seen in another
imaging study investigating the emergence of consciousness from
sleep (72). In the sleep study, midline arousal structures of the
thalamus and brainstem also recovered function well before
cortical connectivity resumed. Thus, the core of human con-
sciousness appears to be associated primarily with phylogeneti-
cally ancient structures mediating arousal and activated by
primitive emotions (36, 73), in conjunction with limited connec-
tivity patterns in frontalparietal networks (74, 75) (Fig. 2).
The emergence from general anesthesia may be of particular
interest to evolutionary biology, as it is observed clinically to prog-
ress from primitive homeostatic functions (such as breathing) to
evidence of arousal (such as responsiveness to pain or eye opening)
to consciousness of the environment (as evidenced by the ability to
follow a command) to higher cognitive function. Unlike the emer-
gence of consciousness over millions of years in phylogeny or
months during the gestational period in ontogeny, the emergence
| Mashour and Alkire
of consciousness from the anesthetized state is a reproducible
model system that can be observed in real time over the course of
hours. Multimodal investigation using neuroimaging and neuro-
physiology, in conjunction with clinical observation and cognitive
evaluation, could uncover key shifts of neural activation or network
organization that support conscious processing. For example, high-
density electroencephalography could be used during recovery
from general anesthesia to measure Phi to help delineate in
humans the threshold for emerging consciousness. Such a thresh-
old could then be compared with other species in the waking state
to determine the relative value with reference to the neural core of
human consciousness. This approach could be applied to any
number of brain network properties, as assessed quantitatively
through graph theoretical methods (76).
Network approacheswhich have broad applicability in mathe-
matics, biology, computer science, and sociologymight be par-
ticularly attractive to test hypotheses across species, where func-
tionally similar cognitive systems may arise from neurobiologically
distinct structures. For example, the mammalian cortex and avian
pallium are histologically distinct (Table 2) (77), but may subserve
similar network functions that can be quantitatively assessed and
compared with human ndings. General anesthesia represents
a way of turning back the evolutionary clock of cognitive function
in humans anddepending on the depthand length of anes-
thetic exposureallows investigators to observe the return of
neural function in a way that could recapitulate phylogeny.
Although not without difculties (including the contamination of
access consciousness, because language is involved in assessing
return of consciousness after anesthesia), advantages of emer-
gence from anesthesia as a model system for the evolution of
consciousness include convenience, reproducibility, real-time
observation, possibility of subjective report of experiences (with
experiments in humans), and amenability to neuroscientic in-
vestigation across multiple species.
When Does Consciousness of the World Arise?
The recent experiments with general anesthesia in humans sug-
gest that phylogenetically ancient structures in the brainstem and
diencephalonwith only limited neocortical involvementare
sufcient to support primitive consciousness. Where, then, does
consciousness arise on the evolutionary timeline? One might be
tempted to conclude that consciousness commenced as our
mammalian ancestors evolved just beyond reptiles and their pre-
dominantly subcortical brains. However, paleontological ndings
suggest that the synapsid line that gave rise to mammals and the
sauropsid line that gave rise to reptiles and birds both diverged
from the primitive anapsid line at a single point 315 million years
ago (78). Furthermore, there is signicant evidence that avian
species are capable of higher cognition and even consciousness
itself (79). For example, birds demonstrate evidence of explicit
episodic recall (i.e., conscious memory of an event) (80) and
theory of mind (i.e., attribution of subjective mental events to
another being) (81). Thus, it would be misguided to try to identify
a single point at which consciousness emerged because evidence
suggests that consciousness evolved along two independent line-
ages. As pointed out by Butler et al. (82), birds and mammals
share a number of homologous traits despite this evolutionary
divergence, including a dramatic increase in their brainbody ra-
tios (compared with reptiles), homeothermy, extended parental
care of offspring, habitual bipedalism, distinct sleep stages, and
complex social interactions. The neurobiology also reects ho-
mologous advances, particularly in the mammalian neocortex and
the avian pallium (Table 2). These advances include the emer-
gence of recurrent or feedback processing, which is not found in
reptiles. Thus, both birds and early mammals are equipped with
a neural substrate consistent with conscious processing: phyloge-
netically conserved brainstem, diencephalic structures such as
thalamus and hypothalamus, and association neocortex (or
equivalent) capable of recurrent processing. All of these struc-
tures appear to play a role as the neural core for primitive con-
sciousness in humans, as evidenced by experiments with
general anesthesia.
The critical role of subcortical structures in consciousness has
been further argued based on clinical observations of hydra-
nencephalic children, who are essentially devoid of neocortex and
yet who still demonstrate some behavioral signs of consciousness
(75). Others have attempted to link the arousal related compo-
nents of consciousness with the contents of consciousness by
placing emphasis on the dynamic recurrent activity that occurs in
the thalamus or through the thalamic reticular nucleus when
consciousness is present (83, 84). As such, the PET study showing
that the emergence of consciousness is correlated with increased
Fig. 2. Brain structures functionally related to primitive emotional arousal
and the return of consciousness following sleep or anesthesia. The primitive
emotional response of air hunger shows activations in brainstem and anterior
cingulate regions; thalamic changes are also seen (73). Subjective emotional
arousal activates similar regions in an event-related functional MRI study of
picture viewing. Reproduced with permission from (85). Midline thalamic and
anterior cingulate arousal is seen with PET neuroimaging when consciousness
rst reemerges following sleep or anesthesia. Reproduced with permission
from (72 and 65). A common brainstem, thalamic, cingulate neuroanatomy
associated with conscious brain activity is seen. Images used with permission.
Table 2. Comparison of neocortex and pallium with respect to requirements for cell assemblies
Requirements for Hebbian cell assembly Structure of mammalian neocortex Structure of avian pallium
Many neurons of the same kind About 85% pyramidal cells High number of multipolar cells
Connections with each other Most synapses are between pyramidal cells Many synapses between multipolar cells
Excitatory connections About 90% of synapses are type 1 (excitatory) Many synapses excitatory
Modiable connections About 75% of synapses are on spines Dendrites are densely spiny
Individual neurons connected to as
many other neurons as possible
About 8,000 synapses per neuron Many synapses per neuron
Distant connections across the network Large amount of white matter Axons more interspersed with neurons
Modied from (77) with permission from Elsevier.
Mashour and Alkire PNAS
June 18, 2013
vol. 110
suppl. 2
activity in primitivebrain regions may reect an arousal-related
response to the test stimulus itself rather than a direct awareness
of the stimuli that is occurring in the thalamus. In either event,
the data clearly show that the neurocircuitry associated with
arousal is fundamental to consciousness. A further recent study
investigating long-term memory encoding also imaged the neural
correlates of subjective emotional arousal. As shown in Fig. 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 (85).
Regarding ontogeny of H. sapiens, peripheral sensory receptors
are thought to be present from 20 wk of gestation in utero. The
developmental anlage of the thalamus is present from around day
22 or 23 postconception, and thalamocortical connections are
thought to be formed by 26 wk of gestation (74). Around the same
time of gestation (2529 wk), electrical activity from the cerebral
hemispheres shifts from an isolated to a more continuous pattern,
with sleepwake distinctions appreciable from 30 wk of gestation.
Thus, both the structural and functional prerequisites for con-
sciousness are in place by the third trimester, with implications for
the experience of pain during in utero or neonatal surgery. It is of
interest to note that the third trimester of human development is
thought to be the period in which the maximal proportion of time
spent in REM sleep occurs across the lifespan (86). This nding
supports the ontogenetic theory of REM sleep as a process of in-
ternally driven neuronal activation that prepares the developing
cortex for the coming inux of sensory stimuli at birth. The theory
of REM sleep as a form of protoconsciousness has recently un-
dergone further elaboration (87).
When Does Consciousness of the Self Arise?
One component of consciousness that seems linked to higher
cognitive abilities is awareness of the self rather than simply
awareness of the environment. One way to test for this possibility
is to use what is known as the mirror self-recognition (MSR) test
(88). In 1970, Gallup found that chimpanzees, but not monkeys,
were able to pass the MSR test (89). This test presupposes that the
experimental subject has sufcient cognitive ability to be aware of
itself as an entity that is distinct from another conspecic. This
ability then denes one form of consciousness (i.e., the ability to
have awareness of ones own awareness or self). In Gallups well-
controlled experiment, the animals were rst allowed ample time
with mirror exposure to allow social responses to their reected
images to diminish greatly. The number of social responses and
the number of self-directed responses were measured before the
animals had a mark covertly placed on their forehead or ear while
they were briey anesthetized. The animals were then allowed to
recover from anesthesia, and some hours later a mirror was
reintroduced. On seeing themselves in the mirror, the marked
chimpanzeesbut not the marked monkeysexhibited mark-
directed responses by spending time investigating the area of the
mark and examining their ngers after touching the mark. The
ndings led Gallup to conclude insofar as self-recognition of
ones mirror image implies a concept of self, these data would
seem to qualify as the rst 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 self-recognition 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.
The MSR test has now been used to examine the ability of
other species to show evidence of self-awareness. Primates that
have passed the MSR test include chimpanzees, orangutans, and
bonobos. The case for the gorilla is equivocal with mostly neg-
ative ndings; several studies have suggested that more socialized
gorillas might be able to pass the test. Humans begin to develop
a sense of self and pass the MSR test starting around 18 mo of
age, and by 2436 mo, almost all western children will show a
positive MSR response (90). The distinction between great apes
and monkeys would seem to provide a clear demarcation in the
capacity for consciousness between species. Numerous studies
have supported this demarcation, with multiple failed attempts
to detect self-awareness in monkeys, despite one recent report to
the contrary (91). However, a number of methodological con-
cerns limit enthusiasm for the one contrary study, and overall the
data continue to suggest that macaques do not evidence MSR
behavior (92). In evolutionary terms, if objective evidence of self-
awareness can be taken as evidence for consciousness, then con-
sciousness as it occurs in the primate with their more fully de-
veloped cortex may have evolved 5 million years ago, at around
the time when great apes split off from the lesser apes.
Mirror-self-recognition may not be limited to the relatively
big-brained great apes. More recent work with other big-brained
creatures suggest the possibility that dolphins, and at least one
African elephant, may also be capable of this response (9395).
As apes, elephants, and cetaceans have a very remote common
ancestor, these ndings would seem to suggest that the mental
machinery prerequisite for self-awareness must be at least as old
as the development of the placental divide in mammals (96).
However, we may be able to take this idea on another path in
evolutionary time. As noted, the cognitive abilities of some birds
are now thought to be comparable to the abilities of some pri-
mates (80). Evidence suggests that the brain development of the
bird, which evolved on a different path from mammals, still has a
conceptually similar thalamocortical structure that can be de-
lineated (43). The cognitive abilities of various birds seem to
correlate with the relative size of the analogous avian prefrontal
cortex. Indeed, the crow-like Corvidae (crows, ravens, magpies,
rooks, jackdaws, and jays) appear to have the most advanced be-
havioral repertoire, as well as the largest prefrontal cortex (pal-
lium) (97). Importantly, a recent report shows Magpies (having
a relatively large prefrontal cortex) exhibit behavior consistent
with MSR (98). This nding, coupled with the current under-
standing of avian neuroanatomy and its well-developed thala-
mocortical structure, suggests that the foundations required for
both consciousness of the world and consciousness of the self may
have formed as early as the amniote radiation (78).
From a cognitive perspective, the meaning of self-awareness
behaviors in a mirror remains somewhat controversial (99). Some
argue that the mirror behavior could be more easily explained
by simple knowledge of ones body. The neurobiology of having
a body sense is something that is highly linked with a sense of
consciousness (100). Perhaps, as stated by Morin (99), all an
organism requires to self-recognize is a mental representation of
its own physical self; the organism matches the kinaesthetic
Fig. 3. Schematic showing relative size of frontal lobe across different
species and the potential capacity for anteriorposterior information ow.
The blue areas represent the prefrontal cortex, and the schematic shows
how the prefrontal cortex proportionally increases in size with increasing
brain size across species. Relative brain size is scaled to the human brain.
Modied from (102) with permission from Elsevier.
| Mashour and Alkire
representation of the body with the image seen in the mirror and
infers that itsme.A number of other arguments against
overinterpreting MSR have been made, yet despite these relevant
concerns, from an evolutionary point of view the presence or
absence of a MSR response is at least a starting point for con-
sidering what having such a response might mean as a basis for the
evolution of consciousness. The MSR response allows one to
question what is functionally and structurally different about
brains that can self-recognize vs. those that cannot.
Why Is Human Consciousness Unique?
We have argued that the brainstem, diencephalon, and limited
association cortex capable of recurrent processing is consistent
with a core or primitive consciousness. However, what accounts
for the richness of human experience in contrast to those of early
mammals or birds? Drawing on the integrated information the-
ory of consciousness, the evolution of more complex brain net-
works capable of synthesizing the outputs of more functionally
diverse modules would result in a higher capacity for conscious-
ness. Indeed, integration of information appears to correlate
positively with tness in articial agents (animats) (27). It is un-
known in biology, however, whether it is the level or quality of
consciousness that differs across species. Although H. sapiens
may have more advanced cognition, it is difcult to imagine that
a sedentary human has a higher level of consciousness than
a highly alert beast in pursuit of prey; the richness of conscious
experience may be what differs. Alternatively, it is possible that
advanced symbolic processing in human cognition eclipses the
subjective characteristics of experience. In other words, cognition
may be potentially opposed to phenomenal consciousness. De-
spite these considerations, human consciousnessespecially the
capacity for self-consciousness and reection/projection in time
seems unique. Although evidence suggests that the core of con-
sciousness is rooted in phylogenetically older structures such
as the brainstem and diencephalon (75), the evolution of that
which is particular to human consciousness may be more closely
associated with the development of the frontal cortex. The rela-
tive size of the frontal lobes with respect to the total neocortex is
roughly the same in modern humans and great apes, but richer
interconnectivity might account for advanced cognition in H. sa-
piens (101). In particular, directed anterior-to-posterior connec-
tivity has been associated with conscious perception and is
dominant in humans (39) but not in rodents (38, 102) (Fig. 3). It
has been suggested that the afferent information from the
periphery converging at the hub of the posterior parietal cortex
becomes, with the expansion of the frontal cortex, dominated by
a strong anterior-to-posterior reafference (103). Indeed, a recent
neural mass model based on structural connectivity data from
diffusion tensor imaging in humans predicts an information ow
from the frontal to the posterior parietal cortex (104). In essence,
this information ow reversal suggests that human consciousness
is more dened by internal dynamics than external stimuli. This
level of information ow reversal may help explain, in part, those
animals capable of a MSR response. According to one theory,
human consciousness is a closed system or oneiric(dream-like)
state that is simply modulated by environmental input (105), a
theory consistent with REM sleep as a building block for human
consciousness. The relative independence from environmental
determination of conscious content would potentially permit
a greater diversity or richness of experience in comparison with
species without dominance of anterior-to-posterior ow. This
independence would also facilitate the projection and simulation
associated with future plans, of clear relevance to survival. It is
important to note, however, that the role of information ow
in consciousness is unclear at this time and requires further
neuroscientic investigation.
The emergence of consciousness on the evolutionary timeline
has been scientically considered at least since the time of
Darwin. The emergence of consciousness from the anesthetized
state may provide a practical and reproducible model for char-
acterizing the real-time evolution of the core neural correlates
required for consciousness of the world and of the self. Using
recent data from general anesthesia in humans, we suggest that
the arousal centers in the brainstem and diencephalonin con-
junction with even limited neocortical connectivity and recurrent
processingcan result in primitive phenomenal consciousness.
By reverse engineering,we postulate that early mammals and
birds possessing these structures (or their equivalents) are capa-
ble of phenomenal consciousness. However, the increased com-
plexity of networks and a functionally dominant prefrontal cortex
in the brain of H. sapiens likely accounts for the unique richness
of the human experience.
ACKNOWLEDGMENTS. G.A.M. is supported by National Institutes of Health
Grant 1R01 GM098578 and the James S. McDonnell Foundation.
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| Mashour and Alkire
... Smooth and rapid recovery from general anaesthesia (GA) is the goal of anaesthesiologists [1]. Therefore, it is necessary to find a method to treat delayed recovery or delayed emergence from anaesthesia [2]. ...
... Recovery and emergence from anaesthesia involve the reestablishment of sensory, motor, and highly ordered cognitive functions and mediate general arousal by subcortical stimulation [3]. Previous studies have reported that noninvasive brain stimulation techniques, including transcranial magnetic stimulation and transcranial direct current stimulation, were used to hasten recovery from anaesthesia in animal models [1,[4][5][6]. ...
... bands of[1][2][3][4],[4][5][6][7][8][9][10][11][12],[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30],[30-45 Hz], [55-100 Hz], [100-140 Hz] and [140-200 Hz]. The total absolute power of the frequency bands was obtained from the band ...
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Background Previous studies have reported that transcranial focused ultrasound stimulation can significantly decrease the time to emergence from intraperitoneal ketamine-xylazine anaesthesia in rats. However, how transcranial focused ultrasound stimulation modulates neural activity in anaesthetized rats is unclear. Methods In this study, to answer this question, we used low-intensity transcranial ultrasound stimulation (TUS) to stimulate the brain tissue of propofol-anaesthetized mice, recorded local field potentials (LFPs) in the mouse motor cortex and electromyography (EMG) signals from the mouse neck, and analysed the emergence and recovery time, mean absolute power, relative power and entropy of local field potentials. Results We found that the time to emergence from anaesthesia in the TUS group (20.3 ± 1.7 min) was significantly less than that in the Sham group (32 ± 2.6 min). We also found that compared with the Sham group, 20 min after low-intensity TUS during recovery from anaesthesia, (1) the absolute power of local field potentials in mice was significantly reduced in the [1–4 Hz] and [13–30 Hz] frequency bands and significantly increased in the [55–100 Hz], [100–140 Hz] and [140–200 Hz] frequency bands; (2) the relative power of local field potentials in mice was enhanced at [30–45 Hz], [100–140 Hz] and [140–200 Hz] frequency bands; (3) the entropy of local field potentials ([1-200 Hz]) was increased. Conclusion These results demonstrate that low-intensity TUS can effectively modulate neural activities in both awake and anaesthetized mice and has a positive effect on recovery from propofol anaesthesia in mice.
... This fact makes it harder for phenomenal consciousness to be subjected to scientific examination -in comparison with access consciousness-, especially regarding its inception during phylogeny and during ontogeny. The developmental onset of basic phenomenal consciousness is yet an interesting topic to study, which sadly has been seldom covered (e.g., Lagercrantz, 2014;Lagercrantz & Changeux, 2009;Mashour & Alkire, 2013). Regarding the developmental onset of phenomenal consciousness, Lagercrantz (2014) argues that in humans it cannot precede the first thalamo-cortical connections at the 24 th gestational week. ...
... This conclusion seems to stem from the thalamic dynamic core theory of phenomenal consciousness (Ward, 2011). The onset of REM sleep at ∼30 th gestational week has been proposed as a functional key-stone for the development of consciousness, for it shifts the electrical pattern of activity and prepares the developing cortex for the sensory influx at birth (Mashour & Alkire, 2013). Anticipating the more general mechanisms underlying the onset of phenomenal consciousness in a minimal organism, recent studies with human brain patterned "cortical" organoids exhibit progressive increases in local field potential recordings, as well as nested oscillatory waves. ...
... A less rocky research avenue stems from the knowledge of that there are some scenarios where consciousness is lost in our species: coma and vegetative states (Laureys et al., 2004;Plum et al., 1998;Sitt et al., 2014), some types of general anesthesia (Alkire et al., 2008;Bola et al., 2018;Bonhomme et al., 2019;Hudetz & Mashour, 2016;Mashour & Alkire, 2013), and during generalized seizures (Arthuis et al., 2009). It can also be severely distorted: hallucinogen drugs (Bayne & Carter, 2018;Stiefel et al., 2014), and dreamless sleep (Darracq et al., 2018;Siclari et al., 2017). ...
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While subcellular components of cognition and affectivity that involve the interaction between experience, environment, and physiology —such as learning, trauma, or emotion— are being identified, the physical mecha�nisms of phenomenal consciousness remain more elusive. We are interested in exploring whether ancient, simpler organisms such as nematodes have minimal consciousness. Is there something that feels like to be a worm? Or are worms blind machines? ‘Simpler’ models allow us to simultaneously extract data from multiple levels such as slow and fast neural dynamics, structural connectivity, molecular dynamics, behavior, decision making, etc., and thus, to test predictions of the current frameworks in dispute. In the present critical review, we summarize the current models of consciousness in order to reassess in light of the new evidence whether Caenorhabditis elegans, a nematode with a nervous system composed of 302 neurons, has minimal consciousness. We also suggest empirical paths to further advance consciousness research using C. elegans.
... and between functional aspects of experience (e.g., how one experience takes conscious priority over another) vs. phenomenal ones (e.g., the experiential difference between seeing two different colors) Seth and Bayne, 2022). This research is largely neurobiologically oriented, focusing on the basis of subjective experience in humans (Boly et al., 2013;Mashour and Alkire, 2013;Hohwy and Seth, 2020;Mashour et al., 2020) and other organisms (Trewavas and Baluška, 2011;Calvo et al., 2017;Baluška and Reber, 2019). Other work considers more generalized definitions, such as measures of information processing that could apply to living and non-living systems (Tononi et al., 2016). ...
... Brain imaging and perturbation studies suggest that conscious experience arises from network-level activity of neurons arranged in precise connectivity structures; whether the relevant networks are primarily cortical/subcortical or frontally/posteriorly located is an ongoing area of investigation (Seth and Bayne, 2022). This has raised the question of exactly when organisms evolved to meet criteria for consciousness, and accordingly there has been work on the biological evolution of consciousness as well (Mashour and Alkire, 2013;Kelz and Mashour, 2019). ...
... Anesthesia may be a fruitful avenue for testing different models of consciousness (Mashour and Alkire 2013;Mashour et al. 2020, p. 785). Almost all vertebrates display sleep-wake cycles and are influenced by anesthetic drugs (Wayson et al. 1976;Neiffer and Stamper 2009;Miyazaki et al. 2017). ...
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The Global Neuronal Workspace theory of consciousness offers an explicit functional architecture that relates consciousness to cognitive abilities such as perception, attention, memory, and evaluation. We show that the functional architecture of the Global Neuronal Workspace, which is based mainly on human studies, corresponds to the cognitive-affective architecture proposed by the Unlimited Associative Learning theory that describes minimal consciousness. However, we suggest that when applied to basal vertebrates, both models require important modifications to accommodate what has been learned about the evolution of the vertebrate brain. Most importantly, comparative studies suggest that in basal vertebrates, the Global Neuronal Workspace is instantiated by the event memory system found in the hippocampal homolog. This proposal has testable predictions and implications for understanding hippocampal and cortical functions, the evolutionary relations between memory and consciousness, and the evolution of unified perception.
... How could we possibly settle these debates about where to draw the line? Many answers to this question of the place of mind in nature have been proposed, such as the eliminativist or illusionist view that no one has consciousness in the sense of possessing qualia (Levine 1983;Dennett 1991;Frankish 2017), the exclusive attribution of consciousness to humans (Macphail 1998), only to the great apes (Bermond 2001), only to mammals and birds (Edelman and Tononi 2000), to all mammals, birds, and non-avian reptiles (Cabanac et al. 2009), to all vertebrates (Mashour and Alkire 2013), to all vertebrates as well as some invertebrate groups such as cephalopods, crustaceans, and insects (Ginsburg and Jablonka 2010;Bronfman et al. 2016; Barron and Klein 2016;Tye 2016), to plants as well (Gagliano 2017;Trewavas et al. 2020), to all living organisms including single-celled ones (Margulis 2001;Reber 2019), and to all entities in the universe (Goff et al. 2020). 6 Views on the presence of consciousness range from none to all. ...
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This goal of this thesis in the philosophy of nature is to move us closer towards a true biological science of consciousness in which the evolutionary origin, function, and phylogenetic diversity of consciousness are moved from the field’s periphery of investigations to its very centre. Rather than applying theories of consciousness built top-down on the human case to other animals, I argue that we require an evolutionary bottomup approach that begins with the very origins of subjective experience in order to make sense of the place of mind in nature. To achieve this goal, I introduce and defend the pathological complexity thesis as both a framework for the scientific investigation of consciousness and as a lifemind continuity thesis about the origins and function of consciousness.
... This framework suggests that different features of experience can in principle vary independently of each other. There is no reason to believeor at least no a priori guaranteethat differences in conscious experience by diverse species all neatly align in one uni-dimensional hierarchy; given recent perspectives on evolution, which leave a unidirectional and teleological perspective behind (Mashour & Alkire, 2013), we expect a diverse variety of types of consciousness in different species. ...
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The science of animal consciousness investigates (i) which animal species are conscious (the distribution question) and (ii) how conscious experience differs in detail between species (the quality question). We propose a framework which clearly distinguishes both questions and tackles both of them. This two-tier account distinguishes consciousness along ten dimensions and suggests cognitive capacities which serve as distinct operationalizations for each dimension. The two-tier account achieves three valuable aims: First, it separates strong and weak indicators of the presence of consciousness. Second, these indicators include not only different specific contents but also differences in the way particular contents are processed (by processes of learning, reasoning or abstraction). Third, evidence of consciousness from each dimension can be combined to derive the distinctive multi-dimensional consciousness profile of various species. Thus, the two-tier account shows how the kind of conscious experience of different species can be systematically compared.
... So, rather than relating to the concepts of discounting reward value or probability, sensation seeking primarily involves an individual's need for stimulation, or arousal 20 . From an evolutionary viewpoint, arousal is thought to act as a coupling mechanism between an organism's internally based needs system, with an externally based situational awareness system and forms the basis for consciousness 21 . Mechanically, arousal may evoke an emotional response which in turn motivates the body into motor action. ...
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Low job satisfaction has been associated with both negative health and negative organizational outcomes. Knowledge on which factors influence job satisfaction remains limited. This study assesses the associations between job satisfaction and three personality traits related to cognitive- and inhibitory control: delay discounting, risk-taking and sensation seeking (DRS-traits). Delay discounting and sensation seeking were inferred using self-reported behavioral data and health measurements for 80,676 participants in the UK Biobank. Multiple linear regression analysis produced beta coefficients and confidence intervals for each DRS-trait and job satisfaction. Analyses were adjusted for age, socioeconomic status and sleep quality. A combination of the three DRS-traits (CDRS) was assessed as well. Delay discounting and risk-taking were associated with, respectively, lower and higher job satisfaction in both sexes. Sensation seeking had no significant association with job satisfaction for either sex. The combined score, CDRS, was only negatively associated with job satisfaction in females but not in males. We discuss that the negative association between delay discounting and job satisfaction may be due to career related delay discounting effects, but also highlight that low job satisfaction itself may also lead to increased delay discounting. Additionally, we discuss why increased risk-taking behavior may have a positive effect on job satisfaction.
... The alternative is that it is involved independently in the former lineages. An assessment of neurobiology reveals several signs of convergent evolution in birds and mammals [68,69]. Both lineages apparently evolved brains better equipped to cater to consciousness compared with what we find in reptiles. ...
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Most multicellular animals have a nervous system that is based on the following three components: (1) sensory cells gather information and send it to processing units; (2) the processing units use the information to decide what action to take; and (3) effector neurons activate the appropriate muscles. Due to the importance of making the right decisions, evolution made profound advances in processing units. I review present knowledge regarding the evolution of neurological tools for making decisions, here referred to as strategies or algorithms. Consciousness can be understood as a particularly sophisticated strategy. It may have evolved to allow for the use of feelings as a ‘common currency’ to evaluate behavioral options. The advanced cognitive capacity of species such as humans further improved the usefulness of consciousness, yet in biological terms, it does not seem to be an optimal, fitness-enhancing strategy. A model for the gradual evolution of consciousness is presented. There is a somewhat arbitrary cutoff as to which animals have consciousness, but based on current information, it seems reasonable to restrict the term to amniotes.
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Background: Previous study reported that low-intensity transcranial ultrasound stimulation (TUS) can significantly decrease time to emergence from anesthesia in rats. However, how TUS modulates neural activity during wakefulness in anesthetized mice is unclear. Methods: In this study, to answer this question, we used ultrasound to stimulate the brain tissue of propofol anesthesia mice, recorded local field potentials in the mouse motor cortex and EMG signals from mouse neck, and analyzed the emergence and recovery time, the mean absolute power, relative power and entropy of local field potentials. Results: We found that TUS can significantly reduce the time from anesthesia to awake; We also found that compared with Sham group, 20 min after TUS during the recovery from anesthesia, 1) the absolute power of local field potentials in mice was significantly reduced at [1-4 Hz] and [13-30Hz] frequency bands, and significantly increased at [55-100 Hz], [100-140 Hz] and [140-200Hz] frequency bands. 2) the relative power of local field potentials in mice enhanced at [30-45 Hz], [100-140 Hz] and [140-200 Hz] frequency bands. 3) the entropy of local field potentials ([1-200Hz]) increased. Conclusion:These results demonstrate that TUS can effectively modulate neural activities during wakefulness in anesthetized mice andhas a positive effect on the recovery from propofol anesthesia of mice.
How do we know who we are? When and how did we become aware of our presence and thoughts? Why do some species develop self-awareness, while others do not? This question of self-awareness and consciousness has puzzled philosophers and scientists alike, from Aristotle and Darwin to Descartes and William James. In his famous "mirror test" thirty years ago, leading researcher Gordon G. Gallup Jr. showed that self-awareness begins with the recognition of one’s reflection in the mirror, an ability that only higher order primates possess. In The Face in the Mirror, Julian Paul Keenan, Gordon G. Gallup Jr., and Dean Falk further explore mirror recognition as the key to understanding the origins of consciousness and its role in our evolution, everyday behavior, and ongoing survival. For the past decade, Julian Paul Keenan and his colleagues have been closing in on the source of self-awareness in the brain. With the advent of MRI technology and other techniques, they have examined the hypothesis that there is a brain network specifically involved in self-recognition. This book shows how the right hemisphere of the brain (where mirror recognition takes place), often relegated to "supporting role" status, may be a more crucial determinant of higher order consciousness. Keenan also shows how recognizing our reflection -- an ability we take for granted -- is linked to such common self-related functions as memory and to emotions like empathy, narcissism, and deception, which play a crucial role in evolution. Insightful, witty, and accessible, The Face in the Mirror plunges the reader into the forefront of thedebate on consciousness in humans and primates. From animals who share our ability for self-recognition, to the development of self-awareness in children, to case studies of patients who no longer recognize who they are, Keenan examines some of the latest evidence in the fields of neurology, psychology, and anthropology and suggests remarkable and surprising results about the function of self-awareness in humans and other primates.
To understand what is happening in the brain in the moment you decide, at will, to summon to consciousness a passage of Mozart's music, or decide to take a deep breath, is like trying to 'catch a phantom by the tail'. Consciousness remains that most elusive of all human phenomena - one so mysterious that even our highly developed knowledge of brain function can only partly explain it. This book traces the origins of consciousness. It takes the investigation back many years in an attempt to uncover just how consciousness might have first emerged. Consciousness did not develop suddenly in humans - it evolved gradually. The book investigates the evolution of consciousness. Central to the book is the idea that the primal emotions - elements of instinctive behaviour - were the first dawning of consciousness. Throughout the book examines instinctive behaviours, such as hunger for air, hunger for minerals, thirst, and pain, arguing that the emotions elicited from these behaviours and desire for gratification culminated in the first conscious states. To develop the theory the book looks at behaviour at different levels of the evolutionary tree, for example of octopuses, fish, snakes, birds, and elephants. Coupled with findings from neuroimaging studies, and the viewpoints on consciousness from figures in philosophy and neuroscience, the book presents a new look at the problem of consciousness.
Placing a patient in a state of general anesthesia is crucial for safely and humanely performing most surgical and many nonsurgical procedures. How anesthetic drugs create the state of general anesthesia is considered a major mystery of modern medicine. Unconsciousness, induced by altered arousal and/or cognition, is perhaps the most fascinating behavioral state of general anesthesia. We perform a systems neuroscience analysis of the altered arousal states induced by five classes of intravenous anesthetics by relating their behavioral and physiological features to the molecular targets and neural circuits at which these drugs are purported to act. The altered states of arousal are sedation-unconsciousness, sedation-analgesia, dissociative anesthesia, pharmacologic non-REM sleep, and neuroleptic anesthesia. Each altered arousal state results from the anesthetic drugs acting at multiple targets in the central nervous system. Our analysis shows that general anesthesia is less mysterious than currently believed.
Summary Awakening from sleep entails rapid re-establishment of consciousness followed by the relatively slow (20‐30 min later) re-establishment of alertness—a temporal dissociation that facilitates specification of the physiological underpinnings of each of these facets of the awakening process. H2 15 O PET was used to assess changes in regional cerebral blood flow (rCBF) upon awakening from stage 2 sleep. Cerebral blood flow (CBF) was most rapidly re-established in centrencephalic regions (e.g. brainstem and thalamus), suggesting that the reactivation of these regions underlies the reestablishment of conscious awareness. Across the ensuing 15 min of wakefulness, further increases in CBF were evident primarily in anterior cortical regions, suggesting that the dissipation of sleep inertia effects (postawakening performance and alertness deficits) is effected by reactivation of these regions. Concomitant shifts in correlation patterns of regional brain activity across the post-awakening period [in particular, a waning negative correlation between prefrontal cortex and mesencephalic reticular formation (RF) activity, and a waxing positive correlation between prefrontal cortex and ventromedial caudate nucleus (CAUD) activity] suggest that the post-awakening reversal of sleep inertia effects may be mediated by more than mere reactivation—it may also involve the functional reorganization of brain activity. Conversely, stable post-awakening correlations—such as those found between the anterior cingulate cortex (ACC) and most other brain regions— may denote the pattern of functional connectivity that underlies consciousness itself.
[opening paragraph] -- Clark: The ‘astonishing hypothesis’ which you put forward in your book, and which you obviously feel is very controversial, is that ‘You, your joys and sorrows, your memories and ambitions, your sense of personal identity and free will are, in fact, no more than the behaviour of a vast assembly of nerve cells. As Lewis Carroll's Alice might have phrased it: ‘You're nothing but a pack of neurons’.’ But it seems to me that this is not so astonishing a statement for a scientist to make. Isn't this what reductionist science has always believed?