Neural Correlates of Consciousness

Introduction

• Thanks to your hard work in the previous units, you have begun to understand the properties of neurons, synapses, and simple circuits.
• We have seen that appropriate combinations of sensory neurons, interneurons, and motor neurons, in combination with bodies, can lead to very interesting behavior.
• It is a quite a distance from pattern generation for behaviors in invertebrates such as slugs to the complex behaviors we see in mammals, primates, and humans. But all of these organisms share neural elements that operate according to the same principles that we have learned earlier in this course.
• Thus, as a glimpse of some of these far more complicated properties, we will discuss a paper that focuses on the neural correlates of consciousness.
• If any of you would prefer to work directly with a simulation of consciousness, and have concrete ideas for how to proceed (and, ideally, get it to run in Javascript) by all means speak to me about this; once we have this working, we will not only provide a far more fitting conclusion to this course, but probably be very well known long after our lifetimes.
• Until we have that opportunity, however, it is exciting to discuss the work that other investigators are doing on this very challenging problem.
• Please read the questions below, and then carefully read the paper that is linked to below; our discussion in class will be focused on answering the questions, based on what we've read in the paper.

Paper to Discuss

Experimental and Theoretical Approaches to Conscious Processing

Questions for Discussion

• Please use the questions listed below as a basis for carefully reading and analyzing the paper.
• Recall our brief discussion of the structure of a scientific paper (The Structure of a Scientific Paper) and how to read it (How to Read a Scientific Paper) at the beginning of the semester.
• Taking the time to carefully and actively read this paper will help you analyze the technical literature in many other contexts.

1. How do the authors (Dehaene and Changeux) define the term "conscious processing"? What do they mean by the term "conscious content"? What is the experimental advantage of defining consciousness in these terms?

2. What is the difference between subliminal or preconscious stimuli as the authors define it? What is binocular rivalry?

3. What are inattentional blindness, the attentional blink, and the psychological refractory period effect? What do they imply about the processing of conscious stimuli?

4. What are objective versus subjective criteria for determining whether an experimental stimulus has reached consciousness? What are the advantages and disadvantages of objective versus subjective criteria?

5. What is the difference between selective attention and conscious access? Which is the focus of this paper?

6. How does brain activity change in response to visible vs. invisible words? (Daheane and Changeux, Figure 1 A) How does brain activity change in response to detected vs. non-detected sounds? (Figure 1B) How does brain activity change in response to inhibitory control by a visible as opposed to an invisible cue? (Figure 1C)

7. How do electroecencephalographic measures of brain activity change when an identical visual stimulus is reported as seen or not seen? (Daheane and Changeux, Figure 2A) How does the P3b event amplitude change as a stimulus is reported to be visible, and what is the evidence for the "ignition" of activity in fusiform cortex? (Figure 2B) What is the evidence from magnetoencephalography that conscious perception affects the power and phase of oscillations in the beta band (13 - 18 Hz)? (Figure 2C)

8. Describe the four signatures of conscious access obtained from human patients with intracranial electrodes (Dahaene and Changeux, Figure 3). How are these related to the "ignition" data shown in Figure 2?

9. How is it possible to reconcile the data that fMRI signals may correlate strongly with conscious perception during binocular rivalry in V1, whereas single cell recordings in V1 largely do not correlate strongly with conscious perception?

10. What is the evidence that a late neuronal response, peaking around 300 ms, is essential for conscious awareness of masked pictures? (Figure 4)

11. What is the evidence that a global fronto-parietal network is essential for the performance of serial tasks requiring effort, or activated by making an error, but not for routine tasks? (Figure 5)

12. What is the Global Neuronal Workspace (GNW) model, and what are the key elements that it incorporates for a theory of consciousness? (Figure 6)

13. How does a simulation of several neural networks that may contribute to consciousness support a central hypothesis of the authors about how consciousness works? (Figure 7)

14. What is the evidence that long distance connections, especially from the pre-frontal cortex to other part of the brain, play a critical role in consciousness? (Figure 8)

15. What is the evidence that loss of overall connectivity in cortex is relevant to consciousness? How is this relevant to anesthesia and to the vegetative state? (Figure 9)

16. What additional evidence would be needed to support or refute the central theory presented in this paper?