By Fang-Zhi Tsai Nov. 21th, 2005.

1. Dehaene, S., & Naccache, L. (2001).Toward a cognitive neuroscience of consciousness: Basic evidence and a workplace framework.Cognition, 79, 1-37. By Fang-Zhi Tsai Nov. 21th, 2005.

2. Outline • Three fundamental empirical findings on consciousness • A theoretical framework for consciousness • The modularity of mind • The apparent non-modularity of the conscious mind • Attentional amplification and dynamic mobilization • Empirical consequences, reinterpretations, and predictions • Structural constraints on the contents of consciousness • Dynamical constraints on consciousness • Neural substrates of the contents of consciousness • Neural substrates of the mechanisms of consciousness

3. Standpoints • The cog. neuroscience of consciousness aims at • determining whether there is a systematic form of information processing and a reproducible class of neuronal activation patterns that systematically distinguish conscious states from other mental states. • Subjective reports are the key phenomena that a cognitive neuroscience of consciousness purport to study. • It may be wrong, ex: Hallucination  Brain-imaging method • The tools of cognitive neuroscience may suffice to analyze consciousness.

4. Three fundamental empirical findings on consciousness • Cognitive processing is possible without consciousness • Attention is a prerequisite of consciousness • Consciousness is required for specific mental operations

5. Cognitive processing is possible without consciousness • Blindsight phenomenon • Perceptual level • Prosopagnosic patient • ERP: shorter P300 for the familiar faces • Semantic level • Neglect patient • Picture-word priming task • the same amount of semantic priming from both hemifields.

6. Cognitive processing is possible without consciousness • Normal subjects • Priming experiments • Masked priming • Brain-imaging studies • Whalen et al. (1998) • passively looking at emotionally neutral faces • Masked faces: neutral vs. expression of fear • Amygdala

7. Attention is a prerequisite of consciousness • Inattentional blindness • Demanding visual discrimination task

8. Consciousness is required for specific mental operations • Durable and explicit information maintenance • Novel combinations of operations • Intentional behavior

9. Durable & explicit inf maintanance • Iconic memory • Monkeys • Single unit recording in infero-temporal (IT) cortex • Masked face--a short-lasting burst of firing (~50 ms) • Unmasked face--a long burst (up to 350 ms)

10. Novel combinations of operations • Stroop-like task • Prime color word • 75% Incongruent trials reversed pattern • No strategic effect was obtained when the word prime was masked or fell outside the focus of attention.

11. Intentional behavior • Blindsight patients • All patients with preserved implicit processing seem to have a similar impairment in using the preserved information to generate intentional behavior. • Automatizable tasks with forced-choice instructions. • Reportability

12. Outline • Three fundamental empirical findings on consciousness • A theoretical framework for consciousness • The modularity of mind • The apparent non-modularity of the conscious mind • Attentional amplification and dynamic mobilization • Empirical consequences, reinterpretations, and predictions • Structural constraints on the contents of consciousness • Dynamical constraints on consciousness • Neural substrates of the contents of consciousness • Neural substrates of the mechanisms of consciousness

13. The modularity of mind • “Modularity” • Functional and neurobiological definition • Automaticity • Specialized neural responses, such as face-selective cells, can be recorded in both awake and anesthetized animals, thus reflecting an automatic computation that can proceed without attention. • Information encapsulation • Increasingly refined analyses of anatomical connectivity reveal a channeling of information to specific targeted circuits and areas

14. The modularity of mind • A given process, involving several mental operations, can proceed unconsciously only if a set of adequately interconnected modular systems is available to perform each of the required operations. • Multiple unconscious operations can proceed in parallel.

15. The apparent non-modularity of the conscious mind • Controlled processing requires a distinct functional architecture which goes beyond modularity and can establish flexible links amongst existing processors. • Besides specialized processors,the architecture of the human brain also comprises a distributed neural system or “workspace” with long-distance connectivity that can potentially interconnect multiple specialized brain areas in a coordinated, though variable manner.

16. The apparent non-modularity of the conscious mind • Communication protocal • Five main categories of neural systems • Perceptual circuits • Motor circuits • Long-term memory circuits • Evaluation circuits • Attentional or top-down circuits

17. Attentional amplification and dynamic mobilization • The orienting of attention causes increased cerebral activation in attended areas and a transient increase in their efficiency. • Top-down attentional amplification is the mechanism by which modular processes can be temporarily mobilized and made available to the global workspace, and therefore to consciousness.

18. Attentional amplification and dynamic mobilization • Dynamic mobilization • A collective dynamic phenomenon that does not require any supervision, but rather results from the spontaneous generation of stochastic activity patterns in workspace neurons and their selection according to their adequacy to the current context. • It would therefore be incorrect to identify the workspace with a fixed set of brain areas.

19. Outline • Three fundamental empirical findings on consciousness • A theoretical framework for consciousness • The modularity of mind • The apparent non-modularity of the conscious mind • Attentional amplification and dynamic mobilization • Empirical consequences, reinterpretations, and predictions • Structural constraints on the contents of consciousness • Dynamical constraints on consciousness • Neural substrates of the contents of consciousness • Neural substrates of the mechanisms of consciousness

20. Structural constraints • Two structure criteria (for conscious availability of inf) • Active representation • The information must be represented in an active manner in the firing of one or several neuronal assemblies. • Bidirectional connectivity with the workspace • Bidirectional connections must exist between these assemblies and the set of workspace neurons, so that a sustained amplification loop can be established.

21. Active representation • Unconscious: • Interaural delay • Conscious: • Tower of Hanoi task • Encoded in hardwired connectivity VS. Generated dynamically through the serial organization of active representations

22. Bidirectional connectivity

23. Dynamic constraints • Two thresholds in human inf processing: • Need to cause any differenciated neural activity • Consciousness threshold

27. Neural substrates of the contents of consciousness • Two categories of the relative studies • Various contents of consciousness • FFA • V5– motion • Brain-imaging vs. lesions • The shared mechanismsthe next section

28. Neural substrates of the mechanisms of consciousness • The cognitive neuroscience literature contains numerous illustrations of these principles, and many of them point to prefrontal cortex (PFC) and anterior cingulate (AC) as playing a crucial role in the conscious workspace.

29. Brian image of conscious effort • Raichle et al. (1994) • Verbal generation task • PFC & AC • Initial task performance: activated • Automatized: vanished • Novel items were presented: recovered • Contrasting conscious & unconscious subjects • McIntosh et al. (1999) • Left PFC • Binocular rivalry • Tong et al. (1998) • infero-temporal (IT) cortex

30. Anatomy and neurophysiology of the conscious workspace

32. This connectivity pattern, which is probably also present in humans, provides a plausible substrate for fast communication amongst the 5 categories of processors that we postulated contribute primarily to the conscious workspace.

33. Take home message • Workplace framework • Many modular cerebral networks • Mobilized by top-down attentional amplification • Self-sustained loop of activation • Long-distance connectivity • Distributed throughout the brain • PFC & AC