Lecture 32: Arousal, Consciousness, and Free Will

What are the various states of arousal?

• alert

• lethargy

• obtundation

• stupor

• coma

Define alert.

normal state of arousal

Define lethargy.

prolonged sleepiness, sluggishness, or serious drowsiness; they can be aroused with moderate stimuli but fall back asleep

Define obtundation.

mental blunting with mild to moderate reduction in alertness and a diminished sensation of pain; tends to sleep more than normal with drowsiness between states

Define stupor.

a state of near-unconsciousness or insensibility; only vigorous stimuli will arouse the person before they go back to an unresponsive state

Define coma.

unarousable unconsciousness, even with pain; reflexes such as posturing don’t count as responses

Describe the Glasgow Coma scale.

• scores range from 3-15

• best eye response (E)

  • 4 - eyes opening spontaneously

  • 3 - eye opening to speech

  • 2 - eye opening in response to pain

  • 1 - no eye opening

• best verbal response (V)

  • 5 - oriented

  • 4 - confused

  • 3 - inappropriate words

  • 2 - incomprehensible sounds

  • 1 - none

• best motor response (M)

  • 6 - obeys commands

  • 5 - localizes to pain

  • 4 - withdraws from pain

  • 3 - flexion in response to pain

  • 2 - extension to pain

  • 1 - no motor response

Which brain lesions can cause changes in arousal?

• diffuse lesions across the hemispheres:

  • cardiac arrest

  • mass lesion causing an increase in intercranial pressure

• small lesions in the ARAS

  • midline thalamus

  • midbrain

  • pons

  • medulla

What are the 3 things in the skull?

• brain

• blood

• CSF

What is the Monroe-Kelli doctrine?

if one thing goes up, either ICP increases (compressing the cortex) or something has to leave

What is ischemia?

lack of blood flow

What is brain herniation?

the brain slips into a different location

What are the types of brain herniations?

• subfalcine

• uncal

• tonsillar

Define subfalcine herniations.

the cingulate cortex falls below the falx

Define uncal herniations.

the uncus goes over the tentorium

Define tonsillar heniations.

cerebellar tonsils go through the foramen magnum

What does uncal herniation result from?

pressure on the temporal lobe causes the uncus to herniate across the tentorium—compressing the midbrain

What does uncal herniation cause?

• diminished level of arousal

• ipsilateral CNIII palsy

  • eyes will dialate

• death if pressure reaches the medulla

What are the treatments for uncal herniation?

• medications to diminish ICP (osmotic agents)

  • hypertonic solutions

• hemicraniectomy

Describe unresponsive wakefulness/PVS.

• after 2-3 weeks of coma, patients will develop the following:

  • diurnal eye opening

  • eye opening in response to arousing stimuli

  • sleep/wake respiratory and movement cycles

  • will often respond reflexively to environmental stimuli

• no purposeful response to stimuli

Describe minimally-conscious state (MCS).

• as in PVS, but occasional command following

• better prognosis than PVA

  • occasional “awakenings” from “coma” reported in the media are typically MCS patients

Describe a locked-in state.

• paralysis of all muscles except those for vertical eye movements and eyelids

• preserved arousal/mentation

• basilary artery thrombosis

  • lesions of pons/midbrain

Describe akinetic mutism.

• profound amotivational state

• due to the lesions of the midline frontal cortex

• easily confused for coma/PVS/catatonia

True or False: Brain imaging of control and PVS patients show that the PVS brain appears to respond nearly normally to external stimuli. Therefore, some patients that meet clinical criteria for PVS may be able to follow commands “cognitively”.

true

How can PVS patients communicate?

through fMRI signals

True or False: Cardiorespiratory function may continue even when the brain is no longer functioning.

true

Describe brain death.

• no brainstem reflexes

• no respiration (let CO₂ ride up to 60 mmHg)

• can still have spinal reflexes such as the triple flex and deep tendon reflexes

• needs to be sure that there is none of the following:

  • sedating meds are on board

  • not hypo/hyperthermic

  • no gross metabolic abnormalities

• confirmatory testing

What types of things are said to be the “easy” problem in studying awarness?

• identifying neural correlates of conscious awareness

• looking for the neural correlate of consciousness (NCC)

What is a common tool for studying the “easy” problem?

bistable images

What is said to be the “hard” problem?

understanding how neural processes produce the subjective feeling of awareness

Describe the Niko Logothetis study with monkeys.

• paradigm: one stimulus, alternating responses

  • the recorded neuron in the inferotemporal cortex responds to faces

  • different stimuli are shown to the two eyes

  • monkey’s percept alternated between starburst and face

  • monkey pulled a lever based on its percept

  • the monkey’s percept (assessed via lever pull) matched neuronal response

Describe the Nancy Kanwisher study with humans using fMRI.

• paradigm: one stimulus, alternating percepts

  • fusiform face area (FFA) responds to faces

  • parahippocampal place area (PPA) responds to locations

  • combined face/place stimulus show

  • subject indicated which stimulus was perceived

  • could predict the subjects percept by measuring which brain area activated

Describe the Itzhak Fried study.

• sensory imagery activates the same brain areas as down sensory percepts

• neurons that respond to the visual percept of dolphin also respond during when imagining a dolphin

What about perceptions in the absence of sensory stimuli (e.g., hallucinations)?

• similar circuits get activated during hallucinations as during sensory-driven perception

• the difference between sensory imagery and hallucinations has to do with the agency of the percept

Define agency.

the sense of volitional control over one’s actions or thoughts

What is the Libet experiment?

1. observe clock

2. note clock position at time of conscious intention (urge to act)

3. perform action

4. report clock position at time of conscious intention (urge to act)

What are the 3 interpretations of the Libet experiment?

• there is no free will; our brain rationalizes all of our actions after the fact

  • many studies have shown that we routinely rationalize explanations for our behavior

  • Libet though that there if “free won’t”

    • think about Stroop inhibition of pre-potent responses”

    • ties into Freud’s structural model of the mind

• there is free will; the Libet paradigm is flawed

  • it is impossible for us to estimate when we came up with the decision to move a muscle

• most of what we do is zombie-like and without deliberation; we consciously consider only a small fraction of our actions