Topic 14: Consciousness Flashcards
(46 cards)
What is the biological basis of consciousness?
natural evolution, as brilliantly by Charles Darwin (1809-1882), over these many million years gave rise to nervous systems as complex as the human brain, arguably the most complex object in the universe
and somehow, through the interactions among its 100 billion neurons, connected by trillions of synapses, emerges our conscious experience of the world and ourselves
What is the “hard problem of consciousness” proposed by Chalmers (1995)?
is the problem of explaining the relationship between physical phenomena, such as brain processes, and experience (i.e., phenomenal consciousness, or mental states/events with phenomenal qualities or qualia)
why are physical processes ever accompanied by experience?
and why does a given physical process generate the specific experience it does - why an experience of red rather than green, for example?
What is the “easy problem of consciousness”?
typically involves pursuing a reductionist approach, such as looking for correlational relationships between brain states and experience (e.g. mind wandering and the default network) that may amount to claims about functionality (e.g. the default network is “for” mind wandering, the visual cortex is “for” seeing, etc.)
What are three general methodological approaches to studying consciousness?
physiological
content-based
theoretical
What are some common examples of altered states of consciousness?
sleep
anesthesia
psychoactive drugs
meditation
various clinical states (e.g. coma)
What is a coma?
various causes of brainstem injury (stroke, CNS infection, hypothermia, metabolic disorder, etc.) can lead to coma
a coma can be described as “… a state of unarousable unconsciousness, characterized by a failure of the arousal/alerting system of the brain (the ascending reticular activating system)
patients in comas do not open their eyes, and only produce minimal motor/auditory responses
What brain regions are involved in comas?
the ascending reticular activating system involves a group of nuclei in the brainstem, including two particularly important ones in the pons that deliver acetylcholine and glutamate to the thalamus
these neurons fire during wakefulness and REM sleep (and GABAergic neurons in the hypothalamus and basal forebrain fire when those other neurons are not, i.e. demonstrating an antagonistic relationship)
comas can therefore be understood as (in part) a failure of this system (the ascending reticular activating system)
based on studying coma patients, it seems that activity in the reticular activating system is necessary for consciousness
What is a vegetative state or unresponsiveness wakefulness syndrome (UWS)?
vegetative patients have their eyes wide open but are considered to be unaware of themselves or their surroundings
they may grimace, cry or smile (albeit never contingent upon specific external stimuli) and move their eyes, head and limbs in a meaningless “automatic” manner
the vegetative state is often, but not always, chronic (the “persistent vegetative state”)
given proper medical care (i.e. artificial hydration and nutrition) patients can survive for many years
What are some examples of various diagnostic criteria for vegetative state/UWS?
no meaningful response to external stimuli
no bladder/bowel control
no sustained visual-pursuit eye movements
no volitional fixation
no purposeful limb movement
~50% global brain metabolic activity relative to baseline (similar to nonREM sleep or anesthesia)
Is recovery possible from a coma or vegetative state?
patients sometimes recover from comas/vegetative state/UWS on their own (without intervention), though there have also been various experimental attempts to expedite/enhance that process
What is locked-in syndrome (LIS)?
similar in some ways to a vegetative state/UWS
a state in which selective supranuclear motor deafferentation produces paralysis of all four limbs and the last cranial nerves without interfering with consciousness
the voluntary motor paralysis prevents the subjects from communicating by word or body movement
usually, but not always, the anatomy of the responsible lesion in the brainstem is such that locked-in patients are left with the capacity to use vertical eye movements and blinking to communicate their awareness of internal and external stimuli
often caused by a stroke in the ventral pons
What is the average time course of diagnosis for LIS?
average time-course of diagnosis for LIS (from injury): 78 days
according to one survey, family members made the original observation that a patient may actually be conscious in 55% of cases (compared to 23% with doctors)
extreme methods of communicating possible (Bauby (1997) dictated his book letter-by-letter, blinking each time his therapist spoke the desired letter from a frequency-ordered list)
What physiological/neurological changes occur when a coma/vegetative state/UWS patient recovers?
while UWS is typically associated with global metabolic changes (e.g., 50% of normal levels), the relationship between abnormal metabolic activity and consciousness is not always straightforward
measurement of metabolic activity alone would therefore seem to lack the sensitivity/specificity to use as a definitive way to categorize/understand what’s happening in the brain of these patients
e.g. some patients recover from UWS without their metabolism returning to normal, and some neurologically healthy patients have “abnormal” metabolism without any accompanying changes in their level of consciousness
Why is measuring connectivity a useful diagnostic to measuring metabolic changes to evaluate consciousness?
using PET, one case study patient was found to have
reduced functional connectivity (relative to a control group) between their thalamus and regions of the lateral PFC and anterior cingulate cortex two weeks after presenting with UWS
restored (“normal”) connectivity in those regions four months after recovery
consistent with the implication that abnormal connectivity is associated with UWS, other UWS patients who fail to recover tend to show persistent abnormal connectivity (within their cortex, as well as between their cortex and thalamus)
What was the Owen et al. (2006) study on detecting awareness?
23 year-old TBI patient diagnosed as being in a vegetative state
Owen et al. (2006) reported activity in certain regions (STG and MTG) was greater for speech vs. noise)
patient was also asked to imagine either:
1. playing tennis
2. walking around their house, visiting each room
What was the Monti et al. (2010) study on detecting awareness?
out of a total of 54 patients (with disorders of consciousness) who were scanned, they found 5 who could modulate neural activity on command
also used the paradigm in Owen et al. (2006) to serve as a yes/no response to a series of autobiographical questions (e.g. if answer to my question is yes, imagine playing tennis)
What are two relevant dimensions for understanding/predicting consciousness?
level of physiological arousal of the brain (which is necessary but not sufficient)
level of awareness (currently ill defined)
What physiological changes occur when we fall asleep?
arousing signals sent to the thalamus and cortex (from the brainstem and basal forebrain) are inhibited
What do the physiological changes occur when we fall asleep result in?
a reduction in connectivity between brain regions
an increase in the activity of certain cortical neurons whose waking activity is not usually correlated
alpha waves are suppressed, theta waves emerge, then delta waves
What physiological changes occur during REM sleep?
characteristics similar to wakefulness
release of ACh (acetylcholine) and glutamate (but not other neurotransmitters that are normally involved in wakefulness: serotonin, norepinephrine, etc.)
a higher proportion of time spent dreaming
what we might consider to be “sleep consciousness” (which may provide another opportunity to study consciousness)
How is simultaneous TMS and EEG used to study sleep?
TMS and EEF can be used in conjunction to assess connectivity, which can be compared during different states of consciousness
e.g. deliver a burst of electrical stimulation with TMS (essentially acting as input to the system), then record the subsequent electrical response of the system via EEG (essentially acting as output for the system)
similar to idea of presenting stimuli and recording the neural response, yet more direct
What was the Massimini et al. (2005) study on simultaneous TMS and EEG during sleep?
TMS-evoked response during nonREM sleep (as compared to wakefulness) produced:
1. a larger initial magnitude of response
2. a response that lasted for a shorter duration, and seemed to affect less widespread regions
the second effect attributed to a reduction in connectivity during nonREM sleep, resulting in the signal remaining “local” (i.e. did not activate a series of other areas)
What are the implications of the Massimini et al. (2005) study on simultaneous TMS and EEG during sleep?
what about the first effect (produced a larger initial magnitude of response)?
seems counter-intuitive, why would we have a stronger response while in a less aware state?
the authors suggest this may relate to the fact that nearby neurons can be more tightly synchronized during nonREM sleep, meaning the response to a directly stimulated area was also more synchronized (which could result in a stronger response)
What were the methods in the Voss et al. (2009) EEG study on lucid dreaming?
required 20 participants to take part in weekly training sessions aimed at helping them experience lucid dreams
after 4 months of training, 4 participants reported reliable being able to successfully induce lucid dreaming (average 3 times/week)
these participants were the brought into a sleep lab and EEG recording were taken while they slept
