This summary contains all the information presented on the slides, plus additional notes I took while attending the lecture.
Since lecture 7 was one of the least attended lectures, I took extra thorough notes on this lecture.
Consciousness – Lecture Notes Interim 2
Consciousness: From Theory to the Clinic, Lecture Notes, Interim 2
Lecture 7: Global Neuronal Workspace Model of Consciousness .......................................................... 2
Lecture 8: Neurotransmitters and Consciousness ................................................................................ 21
Lecture 9: Other Theories of Consciousness......................................................................................... 34
Lecture 10: Levels/States of Consciousness.......................................................................................... 48
Lecture 11: Neuroscience Methods in the Clinic .................................................................................. 57
Lecture 12: Neuroscience in the Clinic .................................................................................................. 69
Lecture 13: The Future of Consciousness ............................................................................................. 83
,Lecture 7: Global Neuronal Workspace Model of Consciousness
What we'll do today
More theoretical explanation of the findings discussed so far (In the previous lectures)
• Global neuronal workspace theory
o GNSW in action
o The role of the thalamus and attention
o Different modes of processing (local vs. Global)
o Anatomy
o The restless brain (resting state dynamics)
o A catalogue of the unconscious (4 stages of processing)
• More on feedforward versus feedback processing
The Global Workspace "In Action"
See also figure 19 in the book
How activity in the Brain evolves over time
Number is presented in one of six location, and a metacontrast map (not directly on the target, but
surrounds the target.
Objective performance → how good as subjects at saying whether the target is bigger or smaller
than 5.
Subjective task → Visibility rating
When SOA increases (B), so does the visibility of the target (C).
You see that the shapes of these curves overlap a lot.
Blue → subliminal
Red → "at threshold" sometimes these stimuli are seen, other times not
Yellow → target is seen
,GNWS Theory
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1. Early feedforward processing is (almost) equal)
Activity in early visual areas is strong around 100 ms after stimulus onset. This is for each of
the masking conditions (see coloured lines under "Masking strength"
This triggers the feedforward sweep
The strength of masking doesn't really matter in this. The initial activation of the brain is
very similar across all levels of masking.
2. Feedforward activation decays with depth
The information in these early visual areas are swept forward to higher visual areas. This is
around 150/200 ms after stimulus onset.
Here you can see clear differences between the masking strength. Weaker masking
creates more activation, strong masks make very weak activation. This illustrates that
activation of fully masked information dies out very quickly in the brain.
3. Crossing of consciousness threshold → late global ignition by "GNW neurons" in parietal and
frontal cortex ("all-or-none process")
At some point, the information in the visual cortex is forwarded all the way to the prefrontal
cortex. Here something funny happens. This is what Dehaene calls "global ignition". There is a
theoretical threshold in the brain which a stimulus has to cross in order for this stimulus to
become conscious. Something in the prefrontal cortex meditates this threshold. Crossing this
threshold is an all or nothing principle (a stimulus either is conscious or is not).
You can see that the subliminal trials die out, they don't really reach/activate the
prefrontal cortex, and the stimuli remain unconscious.
The reason that you still see some activation on "more unconscious" trials, is because
the activation levels shown here are an average of all the activation. For example, the
, red line "at threshold", some targets are seen, but others aren't. The average brain
activation is shown in this graph.
4. Feedback to earlier regions when conscious (thus also all-or-none late processes in earlier
regions)
Once the prefrontal cortex is activated, and the target crosses the threshold, you get global
ignition. This means that the entire brain "lights up". All regions in the brain get activation
after this threshold. This is illustrated with feedback conditions. You can see this feedback
processing at around 300/400 milliseconds after stimulus onset. You can see that earlier
regions get "re-activated". This is also an all-or-none process.
Feedforward processing = Earlier regions (like V1) sends information forwards to higher level
regions
You can see this in the little arrow shown by the masked input brain.
Feedback processing = At some point, regions in front of the brain also connect to regions in
the back of the brain (lower in the hierarchy of the brain). Shown in
the arrows which go to the posterior part of the brain (depicted left
here)
Global ignition: All-or-none conscious access
At threshold:
Sometimes you see it, sometimes not.
(Transition point: similar to the freezing point of water, etc.)
If a signal doesn't cross the signal, you can see that the response is close to none. If it does cross the
threshold, you get a global response
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