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Consciousness and its Disorders - Coggle Diagram
Consciousness and its Disorders
Consciousness in Western Thought
Content from different sensory modalities seamlessly integrated with our ongoing streams of self-generated thought
Has intrinsic qualities or unpleasant sensations
Descartes started things
Was a firm defender of the physical sciences and the mechanical philosophy
Knew what happened to the brain affected the content of consciousness
Argued that the contents of consciousness cannot be physical since at least some of their essential properties are not physical matter
Brain events have spatial extent but qualia do not
Postulated a fundamental divide between physical stuff and thinking stuff
Known as substance dualism today
Dissected human brains until a certain place caught his attention and decided the casual interaction between physical stuff and thinking stuff could only occur in place:
The pineal gland
We now know that the main function of the pineal gland is much more modest one of producing melatonin
Substance dualism is seen as a dead end in the scientific and philosophical investigations of consciousness
Descartes stated there is a contradiction in observing that thinking stuff is causally isolated from matter and simultaneously engages in causal interaction with the pineal gland
Thinking stuff” can spontaneously set physical matter in motion which contradicts the principle of conservation of mechanical energy
Since “ thinking stuff ” is independent from physical matter, substance dualism forbids from the outset any attempt to link consciousness to the other branches of science, which benefit spectacularly from the physical sciences
Cartesian dualism is giving up on achieving a physical explanation of physical explanation of consciousness
Property dualists reject the existence of non-physical stuff but claim matter can have both physical and mental properties
Ex: epiphenomenalism postulate that mental properties exist but are causally inert with respect to physical properties
Interactionist versions of property dualism do not reject the casual power of mental properties
Can be roughly divided into emergentist and non-emergentist versions
For the emergentist mental properties are manifest when physical matter reaches a sufficient level of organization
The emergentist gives up by declaring that these properties are irreducible
They are novel and beyond explanations in terms of physics
Other versions exist such as downward causation
Faces the problem that relating attempted explanations to the body of knowledge developed in physics and other branches of science
For the non-emergentist, mental properties are both fundamental and independent from physical matter
The non-emergentist substance dualist claims the irreducibility of consciousness as a fundamental property of physical reality
Perhaps too keen: as long as a viable operationalization of mental properties is not proposed it is difficult to see any sort of scientific development arising from this and from all other varieties of property dualism
There are two straightforward alternatives to dualism
Proponents of idealism claim the ontological primacy of the mental over the physical
Idealism is not necessarily non-reductive
The challenge is to reduce the physical world and its laws to an explanation in terms of the regularities of mental phenomena: what we call “ phenomenology ” .
This type of “ inverse reduction ” is almost never discussed and even less frequently attempted.
if only consciousness is real then, as far as I am concerned, only my consciousness is real.
Materialism
recently rebranded as physicalism
the ultimate nature of reality is given by matter and the physical laws that govern its behavior
is the default position of most practicing neuroscientists.
Token physicalism
Identical with some physical state of some physical system
The brain yes but it is needed not necessarily be the case
The physical system is irrelevant insofar it instantiates the adequate set of cause-effect relationship
Leads to functionalism
Functionalism
Influential and is the philosophical foundation of cognitive neuroscience
Dominant approach toward relating mind and brain
Mental states are not physical but cannot be reduced to the physics of any particular system
Can be instantiated in many different systems
Declares its autonomy from all other branches of science
Type physicalist
Will not waste time discussing how physical systems other than the brain can generate consciousness
Must face the conceptual and empirical problem of identifying the physical events that correspond to the different types of mental phenomena that are know to occur
The eliminative and revisionist materialists will claim that several types of mental phenomena will either change or vanish in the process of reducing them to brain events
in the same way that phlogiston was eliminated from the ontology of physical entities when combustion was explained by the laws of modern chemistry
Current publishing trends in philosophy, cognitive and brain sciences show us that non-physicalism is on the rise.
The positions gaining new terrain can be broadly categorized as varieties of substance dualism or neutral monism.
The Neural Correlates of Consciousness
Crick and Koch proposed to find the neural correlates of consciousness (NCC)
Is the first line of attack on the scientific problem of conscious perception
Focus on visual perception and the neurobiology of vision
the NCC in the visual domain correspond to minimal set of neural events associated with conscious visual perception
The focus on minimal set is important
Searching for the NCC does not only depend on being a committed physicalist
A corollary is the impossibility offending a minimal set of neural events that only correlate with conscious perception
That perception would not be separable from function -in particular, from the cognitive functions required to issue a report signaling that very perception
Several candidates for the NCC of visual perception have been proposed
Includes:
include 40 Hz cortical and thalamo-cortical oscillations
re-entrant thalamo-cortical loops
activity in thalamic intralaminar nuclei, single unit activity in the inferior temporal cortex
the formation of distributed neural assemblies or coalitions and the all-or-none ignition of activity in frontal, parietal, and temporal cortices
Three features are shared by these proposals
the recruitment of spatially distributed neurons
the involvement of regions receiving input from primary sensory cortices, but not necessarily of the primary sensory cortices themselves
they have been discarded as viable candidates for NCC
Most of these candidate NCC exclude activity in the primary visual cortex
When different stimuli are presented to each eye of a human or non-human primate, the stimuli are not fused into a single conscious percept, but instead alternate spontaneously according to verbal and behavioral reports
Called binocular rivalry
Electrophysiological studies in primates show that activity in V1 neurons does not track the alternation between rival percepts
the firing of certain neurons located higher in the visual processing hierarchy (inferior temporal cortex) presents significant correlation with the reported perceived stimulus
This supports the involvement of those neurons in the NCC of visual perceptions
Lesions in V1 can cause blindsight or unconscious vision
First, damage to extrastriate (i.e. higher order) areas with an intact V1 can also abolish visual perception
Second, external stimulation to these areas can elicit simple visual imagery even when V1 is lesioned
Lesions in areas outside the NCC could nevertheless re-organize the NCC themselves
Much less is known about the putative NCC of conscious perception in other sensory modalities
Magnetoencephalography (MEG) recordings show that consciously detected sounds correlate with high amplitude and long-latency response
both detected and undetected sounds correlate with steady-state responses attributed to activity in the primary auditory cortex
Another MEG study addressed the NCC of somatosensory stimulation, finding very early locking of activity correlated with consciously perceived stimuli in frontal, parietal and somatosensory regions
We see the putative NCC of visual perception being chased into higher-level cortical areas that receive input from primary and secondary sensory regions, but are associated with cognitive functions unrelated to vision
Attention
working memory
decision making
Action planning
Language production
Comprehension
Phenomenal and Access Consciousness
“ Consciousness ” is increasingly seen as a composite concept
Phenomenal consciousness (or P-consciousness) stands for the qualities of the subjective experience: “ what is it like ” to have that experience.
Access consciousness (or A-consciousness) stands for the global availability of conscious content for cognitive function
Can phenomenal consciousness occur without access consciousness and, if so, what kind of experimental paradigm can reveal their dissociation?
Phenomenal consciousness overflows cognitive processing
The sharpness of central vision is caused by light reaching the fovea
a region of the retina densely packed with receptive cells
The angle subtended by central vision is deceivingly small
ghosts of words
can be replaced by things that are not words at all and, as long as your gaze remains fixated, you will not even notice
The dissociation between phenomenal and access consciousness
Sperling ’ s partial report paradigm
An array of letters is shown for a brief time to the subjects after disappearing.
to report the letters that were in the array, they are able to recall a small proportion of them
Subjects might confidently report that they perceived the whole array of letters
was the whole array really consciously perceived, or those letters outside the scope of attention were only seen as a gist, as sketchy visual content
The ghosts of letters give the false impression of being vivid and definite
No such time as the “time of visual perception"
Visual information is distributed in the brain
While 50 ms might be late for some processes to occur, it might not be too late for top-bottom attention to amplify the visual content and make it globally available
There is no “finishing line ” after which visual information enters conscious awareness
Information is processed in a distributed fashion in the brain
Global workspace theory (GWT)
proposed by Baars, Dehaene and colleagues
Equals consciousness with global availability for cognitive processing
Consciousness is access consciousness
Availability is manifest as the all-or-none sustained ignition of frontal, parietal and temporal regions by stimuli that are both strong and attended.
Strong but unattended stimuli can be pre-conscious
Are susceptible to ignite the global workspace and become globally available
will not make it unless “ helped ” by redirecting top-bottom attention to them in a short window of time afterfi rst activating the early sensory areas
Lamme's neural model for conscious perception
Conscious perception occurs in four stages
Given by all possible combinations of the stimuli receiving attention, and activity becoming locally recurrent
Unattended feedforward activity limited to the sensory cortex is wholly unconscious
Attended and globally recurrent activity is accessed consciously
Unattended feedforward activity can extend beyond sensory areas and infl uence behavior without awareness.
Unattended and locally recurrent activity in visual areas
when phenomenal consciousness occurs
The Cognitive Neuroscience of Consciousness and Beyond
Discussing the neuroscience of consciousness circled back to the kind of distinctions made by the philosophical positions
Phenomenal consciousness in terms of the physical stuff that makes up brains
There is room to accommodate both phenomenological and access consciousness in the varieties of substance and property dualism
How to obtain objective evidence of phenomenal consciousness without access to the cognitive processes required to issue reports of any kind?
processing that links the beliefs and desires taken for granted in experimental subject
rational behavior expected from somebody holding those beliefs
undergoing a certain subjective experience
phenomenal consciousness does not deny that objective evidence of its existence can be obtained
The defender of phenomenal consciousness has not denied a causal relationship with access consciousness
Deny the visibility of letters
The subject only saw ghosts of letters
Sets a higher bar as proof for consciousness
An explicit report of consciousness must be issued
Report produced after adequate cognitive processing by a subject who is not willing to deliberately sabotage the experiment.
An exponentially decaying afterimage was present and the subjective visibility was possible after the cue redirected the attention to the corresponding row of the afterimage.
phenomenal vs. access consciousness could boil down to how different individuals experience the experimental paradigm itself
Some subjects might see the letters, even if unattended
Others might see the ghosts of letters, and report them as such;
Could be related to individual characteristics, such as the capacity for visual imagery or biases in perceptual confidence
Subjects should not only be probed by button pressing in the brief intervals before and afterfixation to a cross.
Instead, they should be asked about the nature of their experience in the experiment itself
Characterize the subject’s idiosyncrasies in visual perception, imagery and perhaps even their personality traits
No-Report, No-Access, Ghost-Report and More-Report Paradigms
Aru and colleagues
proposed to disentangle conscious experience itself from its prerequisites and consequences
Visual perception persists after lesion to temporal lobe regions where neurons track perception in binocular rivalry paradigms
these neurons are involved in a post-perceptual process
Not relying on explicit report
e.g. verbal report, button pressing
indirect markers have been used in fMRI experiments to show that parietal but no prefrontal regions are associated with switching of percepts
eye-related markers could indicate that access to attentional processes has occurre
Is a no access paradigm
Manipulating expectancy effects
Experimenters asked subjects to perform a task while geometric patterns changed nearby in the screen
half the subjects were blind to these changes
After asking whether the subjects perceived the geometric patterns, all of them were aware of seeing them in a second run of the experiment
an expectation effect was induceD
Different evoked response potentials were elicited in each condition in the third run focusing on central attention to pattern
late positive deflections (P300) appeared only in the third run of the experiment
suggest that certain predictions of the GWT might refl ect post-perceptual processing that can be disentangled from the conscious event itself.
Expectancy
leads subjects to diffuse their attention in the display and detect the nearby changes in geometric patterns
made of lots of oriented segments simultaneously changing their direction
subjects detect the movement in the same way you would detect that the words around the one where you are fixating your attention start dancing and moving around, even without being able to read those words
subjects were phenomenally conscious of the task-irrelevant stimuli but, alternatively, we could also say that diffuse attention allowed the access of some properties of the stimuli
others could not be accessed
experimenters have implemented, effectively, a “ghost-reporT” paradigm.
some of these paradigms are “ no-report ” paradigms is a misnomer.
some of them are examples of what we could call “ more-report ” paradigms
experimenters must retrospectively assess “ what happened ” by means of extensive questionnaires and open ended interviews
completely isolating conscious experience from its functional prerequisites and consequences
Accounts of phenomenal consciousness place it at an early stage prior to information becoming cognitively accessed
contingent to the allocation of the adequate attentional resources
if attentional resources are graded from center to periphery then access should be graded as well
Pathological and Physiological States of Consciousness
Disorders of consciousness (DOC)
brain injured patients who are awake but do not show behavior that we deem compatible with any kind of conscious content
diagnosing patients along a continuum of severity is very challenging
brain states characterized by a dissociation between consciousness and arousal
These patients are awake and present spontaneous movements, eye openings and preserved sleep-wake cycles
exhibit behavior atfi rst impression incompatible with conscious awareness of their surroundings
are unable to establish and maintain functional communication
DOC occur in a continuum with variable degrees of severity
currently grouped as vegetative state (VS), minimally conscious state (MCS) and confusional state (CS)
VS patients are unable to communicate and display behavior consistent with unconsciousness
MCS and CS patients show behavioral evidence of self or environmental awareness
misdiagnosis of DOC patients occurs in up to 43% of the cases
challenge is to develop objective methods for diagnosis having better sensitivity
diagnosis of DOC is currently based on assessing the behavior of the patients
Advances in non-invasive brain imaging are increasingly being explored to detect consciousness without the need for motor responses
Theoretical accounts of consciousness have contributed to improve our capacity to measure the level of consciousness in these patient
information integration theory (IIT)
proposed by Tononi
builds upon first-person phenomenology to conclude that consciousness is highly differentiated and integrated
the same should apply to its neurophysiological substrate
allowed Tononi to quantify from first-principles the level of consciousness
quantification turns out to be impossible, but can be approximated
has inspired perturbational techniques linking brain complexity to the level of consciousness
Patients with disorders of consciousness can be examined with active or passive neuroimaging
Used to obtain evidence of covert consciousnes
Direct and indirect electrical stimulation and pharmacological interventions have shown some success
brain injured patients are highly heterogeneous and optimism must be restrained until personalized interventions are developed.
DOC and other states of diminished awareness are associated with decreased metabolism and activity in frontal and parietal brain regions, as well as in the thalamus
Scott and Carhart-Harris proposed that serotonergic psychedelics could constitute a promising treatment for DOC
he classical psychedelics, act by agonism at the serotonin 2A receptor (5-HT 2A ), increasing the excitability of the target neurons, and the highest density of 5-HT 2A receptors are located in pyramidal neurons in cortical layer V, preferentially in frontal and parietal brain regions
effects of psilocybin and LSD are known to be opposite to some of the changes seen in DOC patients
serotonergic psychedelics could be useful to revert these changes
some patients face the opposite problem of not being able to get rid of their awareness in order to get a good night of sleep
Even if objective markers show that the patients fell asleep, they still complain of poor sleep quality because, from their perspective, consciousness was present all along
Controlled Departures From Ordinary Consciousness
cognitive neuroscience of consciousness operates under the assumption that all humans share a common functional role for conscious awareness
Mainly the global broadcasting of information in the brain
may break down in the case of patients suffering from certain psychiatric conditions ie schizophrenia
the kind of mind that an experimenter needs to attribute to a subject if he or she wants to interpret the resulting behavioral data as meaningful cannot be taken for granted in a schizophrenic patient.
Psychedelic compounds
may offer an opportunity to chart the landscape of possible minds
Also shows ways to subjectively experience the world
classical psychedelics are reversible and extremely safe, both from the physical and psychiatric points of view
Also called “ psychotomimetics ” , due to the hypothesis that their effects mimic a state of psychosis
psychedelics act by partial agonism at 5-HT 2A receptors
Downstream glutamatergic effects also seem to play a key role in the action of psychedelic compounds
different psychedelics can also target receptors associated with other neurotransmitters and neuromodulators
psychedelics in cognitive and perceptual dimensions
broadband reduction in spectral power, with special emphasis in alpha band power reductions
lpha power decreases are related to enhanced visual imagery during the psychedelic state
could be a consequence of diminished inhibition of task-irrelevant spontaneous activity
electively affect different networks related to specific perceptual and cognitive functions
Some of these changes are correlated with self-reported aspects of the experience
such as the intensity of visual imagery
or disruptions in self-awareness
Can modify other aspects of cognition, such as social cognition and, in particular, pro-social behavior
efforts to investigate the psychedelic state in terms of cognitive functioning have also been undertaken.
psilocybin was shown to impair attention while simultaneously preserving working memory
ince pre-treatment with a 5-HT 2A antagonist did not attenuate these effects, they are likely to be mediated by another serotonin receptor subtype, e.g. 5-HT
Carhart-Harris and colleagues postulated that the effects of serotonergic psychedelics can be related to increased entropy or disorder of brain activity
ncreased entropy is consistent with the enhanced repertoire of brain states observed under psilocybin
more generally with the availability of subjective experiences that depart from those typical of ordinary conscious wakefulness
the psychedelic state of mind could correspond to the extreme of “ expanded consciousness ”
reduced awareness have been linked to diminished entropy or, equivalently, increased order and regularity
he psychedelic state likely requires many independent features to be properly describe
thus resists categorization in terms of a unidimensional framework based on the level of consciousness