Exam 1 Flashcards
What is the common sense definition of consciousness?
Start of Lecture 1
Consciousness is what goes away when one falls into dreamless sleep; interpreting/understanding consciousness from a perspective of loss or absentness
The utility in this definition is that it informs us that consciousness is everything
What is the behavioral definition of consciousness?
Consciousness is associated with the availability of a rich behavioral repertoire
The utility in this definition is that behavior is tangible - it can be studied and observed
Are animals conscious (sophisticated birds and bees)?
Most answer yes according to the behavioral definition of consciousness, for they possess a behavioral repertoire
Birds can be taught categories, even arbitrary catgeories…thus, some say we should grant consciousness to invertebrates
What is the functional definition of consciousness?
Consciousness is the ability to perform certain cognitive functions
“Proper scientific theories of consciousness are those that specify which functions are necessary for consciousness to arise”
By this definition, those who are conscious must be able to perform two different types of information-processing computations:
1. The selection of information for global broadcasting
2. The self-monitoring of those computations
What is the Turing test?
Test to decipher between machine and human
Now, machines can pass the Turing test…new concern: will machiens develop faster than the mechanisms to determine whether they are human?
What is the neurological definition of consciousness?
Established on the basis of levels of consciousness. That is, there are different states of consciousness that are associated with behavioral/cognitive conditions
Glasgow coma scale can be used for this purpose
What is the Glasgow coma scale?
The Glasgow Coma Scale (GCS) is a neurological scale designed to assess a person’s level of consciousness after a brain injury; can be used to examine neurological differences at different levels of consciousness (e.g., wakefulness, locked-in syndrome, dreamless sleep, etc.)
What is prosopagnosia?
Inability to recognize faces; people with prosopagnosia also can’t imagine faces and do not dream of faces
What is the neurophysiological definition of consciousness?
Definition of consciousness that relies on the implication and identification of NCCs
What are neural correlates of consciousness (NCC)?
“The minimal neuronal mechanisms jointly sufficient for any one conscious perception”
For every conscious percept, there will be an NCC. Inducing the NCC will induce the perception; inactivating the NCC will eliminate it.
What are content-specific NCCs?
physical mechanisms whose activity determines a particular phenomenal distinction within an experience
What is a full NCC?
physical substrate supporting conscious experiences in their entirety, irrespective of their specific contents; union of all content-specific NCCs
What are background conditions?
factors that enable consciousness without contributing directly to its content (appropriate glucose, O2 and neuromodulatory milieu, afferent inputs for adequate cortical excitability), sensory input, and motor output chains
What is the philosophical definition of consciousness?
Consciousness is a subjective experience - “what it is to be”
That is, “to be conscious is to have experiences;” experiences meaning “to be” from the inside, like awareness
This is the primary definition we stick with for the purpose of this class and beyond
How is an experience a cause-effect structure?
There is a one-to-one correspondence between the properties of experiences and those of cause-effect structures
In the context of consciousness, an experience is considered a cause-effect structure because it reflects the way our brains process information and generate subjective experiences. This concept can be understood through several key points:
Cause-Effect Mechanisms: Our brains interpret sensory inputs (causes) and produce experiences (effects). This process involves complex neural activities where specific stimuli lead to particular responses or experiences.
Predictive Coding: The brain uses past experiences to predict future events, creating a cause-effect model of the world. Experiences are not just passive reactions to stimuli but are actively constructed by the brain’s predictions and the actual sensory inputs.
Consciousness as Integration: Consciousness integrates information from various sources (causes) to produce a coherent experience (effect). This integration allows for a structured perception of the world, where experiences are linked to specific causes (e.g., seeing lightning and anticipating thunder).
Temporal Dimension: Experiences have a temporal structure where past events influence the perception of current events, and expectations shape the interpretation of sensory information. This temporal aspect underlines the cause-effect nature of experiences, as the sequence of events and the brain’s responses create a continuous flow of consciousness.
Subjective Quality: The subjective quality of experiences, or qualia, reflects the internal cause-effect processes that give rise to the unique way we perceive the world. This includes how emotions, thoughts, and sensations are intertwined and influence each other, forming complex cause-effect relationships that constitute our conscious experience.
Is consciousness self-reflection?
No, to be conscious is to have an experience.
Consciousness can be dissociated from behavior, executive functions, language, episodic memory, working memory, and attention.
Is consciousness of the environment?
No, to be conscious is to have an experience.
Consciousness can be dissociated from behavior, executive functions, language, episodic memory, working memory, and attention.
Is consciousness just of objects?
No, to be conscious is to have an experience.
Consciousness can be dissociated from behavior, executive functions, language, episodic memory, working memory, and attention.
Explain how consciousness can be dissociated from behavior and functions
To be conscious is to have an experience.
Therefore, consciousness can be dissociated from behavior, executive functions, language, episodic memory, working memory, and attention.
Is consciousness just responsiveness?
No, to be conscious is to have an experience.
Consciousness can be dissociated from behavior, executive functions, language, episodic memory, working memory, and attention.
Imagine playing tennis in the vegetative state. This might indicate responsiveness, but does it indicate consciousness?
How are neurons quantitatively distributed throughout the brain?
Cerebral cortex: 16 billion neurons, 100 trillion synapses
Basal ganglia: 0.4 billion neurons
Cerebellum: 70 billion neurons
Spinal cord: 1 billion neurons
Brainstem: < 1 billion neurons
What is the “hard” problem of consciousness?
End of Lecture 1
“…imagine that there is a machine, whose structure makes it think, sense, have perceptions;
we could conceive it enlarged, keeping the same proportions, so that we could enter into it, as into a mill.
…when inspecting its interior, we will find only parts that push one another, and never anything which we could explain a perception.”
How do we determine full NCC?
Start of Lecture 2
contrast conscious vs. unconscious states
How do we determine content-specific NCC?
contrast conscious states where a specific conscious content is present vs. absent (e.g., via tasks)
What is problematic with regard to the diagnoses of minimally conscious states and vegetative states?
40% misdiagnosis rate
Does responsiveness = consciousness?
No, this is an important distinction when reviewing the NCC
You can be unresponsive but still conscious (e.g., dream states, paralysis, etc.)
Describe lesion studies as a type of neuroscientific evidence for NCCs
Lesion studies are causal - strong evidence for a given structure being necessary or not; plasticity may lead to functional reorganization in chronic cases
Describe stimulation studies as a type of neuroscientific evidence for NCCs
Stimulation studies are perturbational - immediate effects provide strong evidence for a given structure being causally involved; non-specific effects may be related to network recruitment
Describe recording and neuroimaging studies as a type of neuroscientific evidence for NCCs
Recording and neuroimaging studies are correlational - can help study a large number of different conditions, but correlation versus causality may be more difficult to assert - ideally requires meta-analysis to quantify consistency of results across many different conditions
Are the cerebellum or hippocampus required for consciousness (i.e., are they NCCs)?
Strong evidence that neither the cerebellum nor hippocampus are required to be conscious
Is the cortico-thalamic system important for consciousness (i.e., is it an NCC)?
Strong evidence that cortico-thalamic system is important for consciousness
Are the posterior brain regions important for consciousness (i.e., are they NCCs)?
Strong evidence that posterior brain regions are important for consciousness
Are feedback connections important for consciousness (i.e., are they an NCC)?
Strong evidence that feedback connections are important for consciousness
Which brain regions have strong evidence for their role, or lack thereof, in consciousness (i.e., what are the most likely NCCs)?
Some of the evidence for the NCC is pretty strong:
- Neither the cerebellum nor hippocampus is required to be conscious
- Cortico-thalamic system is important for consciousness
- Posterior brain regions are important for consciousness
- Feedback connections are important for consciousness
What brain regions remain the objects of debate regarding their role in consciousness as NCCs?
Some cases remain the objects of debate regarding role in consciousness:
- Role of the striatum is debated with regard to consciousness
- Role of the thalamus is debated with regard to consciousness
- Role of the claustrum is debated with regard to consciousness
- Role of primary versus higher-level cortical regions is debated with regard to consciousness
- Role of prefrontal cortex is debated with regard to consciousness
- Role of different cell types or cortical layers are debated with regard to consciousness
What is the result of widespread lesions of the corticothalamic system with regard to consciousness?
Widespread lesions of corticothalamic system cause irreversible coma; this is evidence for the corticothalamic role in consciousness (strong potential to be NCC)
Is spinal cord activity an NCC?
No, the spinal cord plays no role in consciousness (e.g., quadraplegic)
What is the result of ablation, agenesis, or degeneration of the cerebellum with regard to consciousness?
Complete ablation, agenesis, or degeneration of the cerebellum hardly affects consciousness (aligns with strong evidence that cerebellum is not an NCC)
This is bizarre because the cerebellum has 4x more neurons than the cerebral cortex
Why is it surprising that the cerebellum has little effect on consciousness?
Cerebellum has 4x more neurons than the cerebral cortex
What is the result of hippocampal lesions with regard to consciousness?
Bilateral hippocampal lesions do not cause unconsciousness, but may cause decrease in visual imagery and decrease in visual contents of consciousness during mind wandering (aligns with strong evidence that hippocampus is not an NCC)
What is the result of basal ganglia lesions/degeneration with regard to consciousness?
Bilateral basal ganglia lesions/degeneration do not cause unconsciousness; seen in a child who was bedridden and had no verbal skills as a result of basal ganglia degradation yet maintained consciousness (basal ganglia and striatum role in consciousness still object of debate)
What is the result of akinetic mutism (dysfunction of fronto-striatal circuits AKA basal ganglia and medial frontal cortex) with regard to consciousness?
Patients with akinetic mutism (dysfunction of fronto-striatal circuits, specifically basal ganglia and medial frontal cortex) display decreased responsiveness but typically remember everything after episode ends (i.e., fronto-striatal circuits, including basal ganglia, play no role in consciousness, but true role is still object of debate)
What neurotransmitter is the best indicator of consciousness?
Acetylcholine (ACh) is the best neurotransmitter indicator if consciousness as it is elevated during both wake and REM sleep (aka dream state).
The problem with labeling ACh as the “neurotransmitter of consciousness) is that dreaming doesn’t always occur during REM, meaning their are unconscious periods of REM (double dissociations between arousal and consciousness).
What is the effect of claustrum stimulation with regard to consciousness?
Claustrum stimulation was reported to cause unconsciousness.
However, bilateral claustrum lesions/degeneration do not cause unconsciousness.
Therefore, role of claustrum in consciousness (as NCC) is up for debate.
What is the result of claustrum lesions/degeneration with regard to consciousness?
Bilateral claustrum lesions/degeneration do not cause unconsciousness.
However, claustrum stimulation was reported to cause unconsciousness.
Therefore, role of claustrum in consciousness (as NCC) is up for debate.
What evidence exists regarding the thalamus and thalamic systems with regard to consciousness (i.e., is the thalamus an NCC)?
Coma and vegetative state can be observed after bilateral thalamic lesions, BUT these lesions usually also involve neighboring white matter tracts connecting to the brainstem arousal centers.
Moreover, pure thalamic lesions do not cause coma.
Also, loss of consciousness during anesthesia coincides with cortical slowing while thalamus is still awake.
Furthermore, during REM/paradoxical sleep (PS), there is preserved cortical arousal while thalamus is asleep. That is thalamus off does not equal loss of consciousness. If you lesion the thalamus, you can remain conscious.
Therefore, role of thalamus with regard to consciousness (as NCC) is up for debate. Based on this information, general consensus is that thalamus is not an NCC.
What evidence exists regarding the primary sensory cortices with regard to consciousness (i.e., are the primary sensory cortices an NCC)?
Primary sensory cortices activity is preserved during loss of consciousness in deep sleep and anesthesia (seen in a rat model), serving as evidence that primary sensory cortices may not play a role in consciousness.
Moreover, higher-level sensory areas can also be activated unconsciously, such as those for emotional stimuli.
However, high decodability for conscious contents is found in V1 and V2 in some working memory studies.
Therefore, role of primary sensory cortices with regard to consciousness is up for debate.
What is the dual-stream model, and how is it involved in consciousness?
There are syndromic dissociations in lesion cases, leading many to develop the idea of independent streams for perception and action.
“Where” stream is the dorsal stream.
“What” stream is the ventral stream.
However, “simple” lesion cases can actually have more widespread network consequences, such as focal macroscopic lesions, which can lead to subtle, more widespread cortical thinning. Moreover, somatosensory feedback may guide actions in patients with visual form.
Also, dorsal stream can activate for “what,” and unconscious activation of ventral stream can be observed.
Therefore, ventral stream activity is not sufficient for consciousness.
How are fronto-parietal regions impacted by unconsciousness?
There is a common decrease in fronto-parietal metabolism in coma, vegetative states, anesthesia, and sleep.
Moreover, anticorrelations between fronto-parietal networks and the default network vanish with unconsciousness.
What is the relationship between fronto-parietal regions and the default mode network, and how does this relate to consciousness?
There are anticorrelations between lateral fronto-parietal regions and the default mode network.
However, anticorrelations between frontoparietal networks vanish with unconsciousness.
What sensory networks best differentiate minimally conscious states from vegetative states?
Lower-level sensory networks best differentiate minimally conscious states from vegetative state patients at the single-subject level.
FDG uptake in peristriate visual cortex (BA 18) had the highest indiviudal regional classification rate across the pooled cohort, with an AUC of 0.90.
What is the result of prefrontal cortex resections/lesions with regard to consciousness?
Large prefrontal cortex resections/lesions do not lead to unconsciousness, supporting the idea that much of the anterior prefrontal cortex plays no role in consciousness (controversial NCC).
Another study conducted complete prefrontal cortex resections in monkeys and found that there was also no loss of consciousness.
What is the result of posterior traumatic brain injury with regard to consciousness?
There is the potential for a persistent vegetative state after posterior traumatic brain injury, aligning with idea that posterior brain regions are important for consciousness.
Damage to the corpus callosum or dorsolateral upper brainstem is a strong predictor for permanent loss of consciousness.
Moreover, restricted diffusion in posterior brain predicts outcome after anoxic brain injury (possible reason behind this LOC).
What is the result of prefrontal and posterior cortex lesions with regard to consciousness?
Large prefrontal lesions do not cause unconsciousness.
Large posterior brain lesions predict permanent coma/vegetative state, aligning with idea that posterior brain regions are important for consciousness (likely NCC).
How is feedback connectivity affected by loss of consciousness?
There is decreased feedback connectivity during loss of consciousness induced by anesthesia and in vegetative states, aligning with the idea that feedback connections are important for consciousness (likely NCC).
Specifically, frontal to parietal connectivity impacted during LOC.
In particular, blockade of cortical feedback to apical dendrites of cortical neurons may be responsible for loss of consciousness during anesthesia.
How does feedback connectivity differ based on perception of somatosensory stimuli?
There is increased feedback connectivity for perceived compared to unperceived somatosensory stimuli.
Moreover, stimulus perception is suppressed when disrupting feedback connectivity by backward masking.
This may provide some insight with regard to the fact that feedback connectivity is important for consciousness.
Describe the connectivity of layer 5b cells
Large, thick-tufted pyramidal cells of layer 5b project mainly to subcortical structures and are likely involved in cortico-subcortical loops
Describe the connectivity of layers 2/3 and 5a/6 (IT) cells
End of Lecture 2
Thin-tufted pyramidal cells of layers 2/3 and 5a/6 (IT) have cortico-cortical connections and are more heavily interconnected.
These layers may be important for consciousness, as they receive information from the higher order cortex.
Thin-tufted pyramidal cells of layers 2/3 are the most heavily interconnected and show the most specific responses.
What is the importance of activating (arousal) systems?
Activating (arousal systems are important to initiate and/or maintain wakefulness. They promote EEG desynchronization and behavioral arousal.
How does sleep relate to disconnection?
Sleep is a state of partial sensory disconnection
Describe EEG and intracellular characteristics of wake state, SWS (NREM), and REM
At an EEG level, SWS (NREM) has large, slow waves, and intracellular recordings show periods of “silence” where the membrane is hyperpolarized.
In REM, intracellular recordings show a significantly heightened number of action potentials relative to wake and SWS.
The EEG of REM is notably similar to that in a wakeful state, even experts have a hard time differentiating between awake EEG trace and REM EEG trace.
How many activating systems are there?
There are many (>15) activating systems. About half have been characterized only in the last few years, using genetic (optogenetic/chemogenetic tools).
What are the activating systems of the brainstem?
The activating systems of the brainstem are:
1. Glutamate (RF)
2. Noradrenaline (LC)
3. Acetylcholine (LTD + PPT)
4. Serotonin (DR)
5. Dopamine (VTA, vPAG)
What are the activating systems of the hypothalamus?
The activating systems of the hypothalamus are:
1. Histamine (TMN)
2. Orexin/hypocretin (LH)
3. Glutamate/GABA (SuM)
4. GABA (LH 1, 2)
What are the activating systems of the basal forebrain?
- Glutamate
- Acetylcholine
- GABA
What are the two major types of activating/arousal systems?
The two major types of arousal systems are:
1. Noradrenaline, orexin, H, serotonin
2. Acetylcholine (ACh), dopamine
The ACh, DA arousal system is much more active during sleep than the other system. It mediates dreaming during sleep and has nothing to do with disconnection.
The NA, Ore, H, 5-HT system mediates disconnection, meaning its silence is necessary for sleep/disconnection.
How has optogenetic/chemogenetic stimulation been so useful with regard to activating/arousal systems?
Optogenetic + chemogenetic stimulation has allowed us to establish distinct pieces of the ARAS compared to the old view, which was more or less a jumbled mess with little to no specificity.
How was the ascending reticular activating system (ARAS) discovered?
In a cat brain during anesthesia, EEG showed SWS traces. Then, an electrical stimulation was given. This electrical stimulation desynchronized the EEG, lending to the discovery of the ARAS system.
Describe the effects of the EEG desynchronization of the ascending reticular activating system (ARAS)
In a cat brain during anesthesia, EEG showed SWS traces. Then, an electrical stimulation was given. This electrical stimulation desynchronized the EEG, lending to the discovery of the ARAS system.
With regard to the ARAS system EEG desynchronization:
- Effect can be unilateral if electrical stimulation is weak
- Effect persistent after full atropinization (cholinergic antagonist)
- Effect is not due to antidromic stimulation of the pyramidal tract
- Effect is not due to orthodromic stimulation of the specific sensory pathways
- Effects can be mimicked by stimulation of the intrathalamic nuclei, but persists after their lesion (some parts of the thalamus are important for ARAS effects)
What is the reticular formation?
The reticular formation forms the core of the brainstem and most reticular neurons are Golgi type I neurons
How can the ARAS system be divided?
We can divide the ARAS systems on the basis of their projections, some dorsal (thalamic) and some ventral (hypothalamic-BF)
What is the role of noradrenaline (NA) and dopamine (DA) with regard to arousal systems?
Noradrenaline (NA) and dopamine (DA) play a role in the response to novelty, reward
