Consciousness (Lecture 5)

What are some disorders of consciousness?

Coma, brain death, Minimally consciousness, vegetative state

What does consciousness require?

Wakefulness and awareness

Disorders of consciousness

A state where consciousness is impaired by damage to the brain

Locked-in syndrome (LIS)

patients who are aroused and aware but who cannot move except to make eye movements

Total locked-in syndrome: eyes cannot move either

Vegetative state (VS)/unresponsive wakefulness

syndrome (UWS)

Patients who are awake but not aware of themselves and their surroundings

Minimally conscious state (MCS)

Patients who are aroused and show fluctuating signs of awareness without being able to functionally communicate

EMCS (Emergence from minimally conscious state)

Occurs when patients can accurately communicate or functionally use objects

How can you differentiate between the different disorders of consciousness?

There is a scale of diagnostic criteria for each disorder of consciousness, plus locked-in syndrome and emergence from minimally conscious state

An active brain of a healthy participant responds to subconsciously perceived stimuli (numbers, letters, music etc) without the conscious experience of the participant (e.g under anaesthesia and sleeping). What implications does this have?

Activation of a brain region has nothing to do necessarily with consciousness

Could be the brain subconsciously perceiving the stimulus

—> Cannot determine consciousness by activation of a brain region

Functional connectivity

how regions of brain connect with each other (during rest)

Default mode network

the regions of the brain that are active while in a resting state

How can we test the integrity of the default mode network?

With an MRI scan showing the connections while the participant is at rest

What were the findings of the default mode network MRI scan?

Locked-in-syndrome: Default mode network the same as in healthy patients

MCS: Less

VS: Even less

Coma: almost nothing

Brain death: Almost nothing

PET measures the amount of glucose uptake in the brain (or rather, the amount of energy consumed by the brain). What can this predict?

Amount of uptake predicts likelihood of recovery from unconscious state

Active paradigms

Asking the people to do something and checking brain activity

Describe the experiment about playing tennis and walking around the house

A patient in a vegetative state was asked to imagine playing tennis or walking inside their house, which lit up two distinctive brain regions. That way, the patient could answer questions (e.g. think of playing tennis if the answer is yes).

This works for maybe 1/10 patients

What are some characteristics of the tennis/house task?

Not very sensitive: Not responding does not mean patient is unconscious -- could be a memory, language or other deficit preventing them from responding

But: Very specific: A positive effect can be safely considered as reflecting the presence of consciousness

This is why researchers are currently trying to find more sensitive tests

How can we test the connectivity of the brain?

Stimulate the brain using TMS, then measuring the brain activity using EEG

Sleep vs awake: Brain is more connected while awake than asleep, meaning that signal is more local when asleep

Lack of "spreading of activation" during sleep (aka loss of consciousness)

How can we measure the connectivity of the brain?

with the "Perturbational Complexity Index" -- measures how complex the connections in the brain in people who are unconscious are — the more, the more consciousness there is.

The PCI is a number between 0 and 1. At what point is it concluded that there is no consciousness?

More or less score of 0.3 is the score between consciousness and unconsciousness

What is the clinical assessment on the level of consciousness based on?

It is based primarily on observation of spontaneous and stimulus-evoked behaviors

How is arousal, how is awareness measured?

Arousal is measured by eye-opening, whereas awareness is assessed by patient’s command-following or the assessor’s search for other nonreflexive behaviors

Why is awareness misdiagnosed in 40% of cases when it’s only based on clinical consensus?

There is a significant risk that decreased behavioral responsiveness in brain-damaged patients may be due at least partially to motor impairment

How long does it take to wake up from a coma?

Around 3 weeks, otherwise it’s “Chronic coma”

Following waking up, you are either in a vegetative state, locked-in syndrome, or be brain dead

After being in a vegetative state, what are the next steps?

Either

Vegetative state - minimally conscious state- confusional state - increasing independence

Or: Permanent vegetative state - death

Non-traumatic brain injuries

Anoxic brain injuries: Complete lack of oxygen for four or more minutes

Hypoxic brain injuries: Due to a restriction of oxygen supplied to the brain

Prognosis is worse for non-traumatic brain injuries

Traumatic brain injuries

Direct damage to the brain causing death of brain cells (Falls, accidents, stroke)

Coma

No wakefulness (therefore, no awareness), no response to environment. Some comatose patients breathe on their own, some need a machine