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COGNITIVE SCIENCE: FREE WILL AND THE BRAIN

The following points are made by S.S. Obhi and P. Haggard (American Scientist 2004 92:358):

1) In 1983, Benjamin Libet and his colleagues at the University of California San Francisco published a profoundly influential paper on the source of human control. In this study, participants watched a small clock hand that completed one full revolution in 2.56 seconds. While fixated on the clock, a participant voluntarily flexed his wrist at a time of his choosing. After the movement, the clock hand continued to rotate for a random time and then stopped. Then, a participant reported the position of the clock hand at the time when she first became aware of the will to move. Libet and his colleagues called this subjective judgment W, for "will". In other parts of the experiment, participants judged when they actually moved, and Libet called this judgment M, for "movement". The timing of the W and the M told Libet and his collaborators when -- subjectively speaking --a participant formulated a will to move and actually moved.

2) In addition, Libet's team measured two objective parameters: the electrical activity over the motor areas of the brain, and the electrical activity of the muscles involved in the wrist movement. Over the motor areas, Libet recorded a well-known psychophysiological correlate of movement preparation called the "readiness potential" (RP), which Hans H. Kornhuber and Lueder Deecke first described in 1965. The RP is measured using electroencephalographic recording electrodes placed on the scalp overlying the motor areas of the frontal lobe, and appears as a ramplike buildup of electrical activity that precedes voluntary action by approximately 1 second. By also recording the electrical activity of the muscles involved in the wrist movement, Libet precisely determined the onset of muscle activity related to the RP.

3) Libet and his colleagues examined the temporal order of conscious experience and neural activity by comparing the subjective W and M judgments with the objective RP and muscular activity. First, the investigators found that, as expected, W came before M. In other words, the subjects consciously perceived the intention to move as occurring before a conscious experience of actually moving. This suggests an appropriate correspondence between the sequence of subjective experiences and the sequence of the underlying events in the brain. But Libet also found a surprising temporal relation between subjective experience and individual neural events. The actual neural preparation to move (RP) preceded conscious awareness of the intention to move (W) by 300 to 500 milliseconds. Put simply, the brain prepared a movement before a subject consciously decided to move. This result suggests that a person's feeling of intention may be an effect of motor preparatory activity in the brain rather than a cause. As Libet himself indicated, this finding ran directly contrary to the classical conception of free will.

4) Considering all the existing data, the brain is apparently going full speed ahead well before a person experiences the conscious intention of moving. Consequently, no role appears for conscious processes in the control of action -- or so it might seem. Although research casts doubt on whether conscious processes cause actions, the data remain consistent with the idea that conscious processes could still exert some effect over actions by modifying the brain processes already under way. The fact that conscious awareness of intention precedes movement by a few hundred milliseconds means that a person could still inhibit certain actions from being made.(1-5)

References (abridged):

1. Haggard, P. 2001. The psychology of action. British Journal of Psychology 92:113-128.

2. Haggard, P., and S. Clark. 2003. Intentional action: conscious experience and neural prediction. Conscious Cognition 12(4):695-707.

3. Haggard, P., S. Clark and J. Kalogeras. 2002. Voluntary action and conscious awareness. Nature Neuroscience 5(4):382-385.

4. Haggard, P., M. Taylor-Clarke and S. Kennett. 2003. Tactile perception, cortical representation and the bodily self. Current Biology 13(5):R170-173.

5. Haggard, P., and B. Whitford. 2004. Supplementary motor area provides an efferent signal for sensory suppression. Cognitive Brain Research 19(1):52-58.

American Scientist http://www.americanscientist.org

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CONSCIOUSNESS AND COMPLEXITY

The following points are made by Giulio Tononi and Gerald M. Edelman (Science 1998 282:1846):

1) What is the neural substrate of conscious experience? While William James (1842-1910) concluded that it was the entire brain (1), recent approaches have attempted to narrow the focus: are there neurons endowed with a special location or intrinsic property that are necessary and sufficient for conscious experience? Does primary visual cortex contribute to conscious experience? Are brain areas that project directly to prefrontal cortex more relevant than those that do not (2)? Although heuristically useful, these approaches leave a fundamental problem unresolved: How could the possession of some particular anatomical location or biochemical feature render some neurons so privileged that their activity gives rise to subjective experience? Conferring this property on neurons seems to constitute a category error, in the sense of ascribing to things properties they cannot have (3).

2) The authors pursue a different approach. Instead of arguing whether a particular brain area or group of neurons contributes to consciousness or not, their strategy is to characterize the kinds of neural processes that might account for key properties of conscious experience. The authors emphasize two properties: conscious experience is integrated (each conscious scene is unified) and at the same time it is highly differentiated (within a short time, one can experience any of a huge number of different conscious states). Neurobiological data indicates that neural processes associated with conscious experience are highly integrated and highly differentiated.

3) Consciousness, as William James pointed out, is not a thing, but a process or stream that is changing on a time scale of fractions of seconds (1). As he emphasized, a fundamental aspect of the stream of consciousness is that it is highly unified or integrated. Integration is a property shared by every conscious experience irrespective of its specific content: Each conscious state comprises a single "scene" that cannot be decomposed into independent components (5). Integration is best appreciated by considering the impossibility of conceiving of a conscious scene that is not integrated, that is, one which is not experienced from a single point of view. A striking demonstration is given by split-brain patients performing a spatial memory task in which two independent sequences of visuospatial positions were presented, one to the left and one to the right hemisphere. In these patients, each hemisphere perceived a separate, simple visual problem and the subjects were able to solve the double task well. Normal subjects could not treat the two independent visual sequences as independent, parallel tasks. Instead, they combined the visual information into a single conscious scene and into a single, large problem that was much more difficult to solve.

4) In summary: Conventional approaches to understanding consciousness are generally concerned with the contribution of specific brain areas or groups of neurons. By contrast, the authors consider what kinds of neural processes can account for key properties of conscious experience. Applying measures of neural integration and complexity, together with an analysis of extensive neurological data, leads to a testable proposal -- the dynamic core hypothesis -- about the properties of the neural substrate of consciousness.(4)

References (abridged):

1. W. James, The Principles of Psychology (Holt, New York, 1890)

2. F. Crick and C. Koch, Cold Spring Harbor Symp. Quant. Biol. 55, 953 (1990) ; Nature 375, 121 (1995); S. Zeki and A. Bartels, Proc. R. Soc. London Ser. B 265, 1583 (1998)

3. G. Ryle, The Concept of Mind (Hutchinson, London, 1949)

4. G. M. Edelman, The Remembered Present (Basic Books, New York, 1989); ___ and G. Tononi, Consciousness: How Matter Becomes Imagination (Basic Books, New York, in press); see also G. Tononi and G. M. Edelman, in Consciousness, H. Jasper et al., Eds. (Plenum, New York, 1998). pp. 245-280

5. In this context, a "conscious state" is an idealization, exemplified by viewing a rapid succession of slides.

Science http://www.sciencemag.org

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NATURALIZING CONSCIOUSNESS: A THEORETICAL FRAMEWORK

The following points are made by Gerald M. Edelman (Proc. Nat. Acad. Sci. 2003 100:5520):

1) Since Descartes' dualistic proposal (1), consciousness has been considered by many to be outside the reach of physics (2), or to require strange physics (3), or even to be beyond human analysis (4). Over the last decade, however, there has been a heightened interest in attacking the problem of consciousness through scientific investigation (5). To succeed, such a program must take account of what is special about consciousness while rejecting any extraphysical assumptions. It must then construct a theory to account for the properties of consciousness and provide a framework for the design and interpretation of experiments.

2) Scientific understanding of consciousness in neural terms requires the acceptance of a number of constraints. Any account of consciousness must reject extraphysical tenets such as dualism, and thus be physically based as well as evolutionarily sound. Consciousness is not a thing but rather, as William James (1842-1910) pointed out, a process that emerges from interactions of the brain, the body, and the environment. It is a multidimensional process with a rich variety of properties. Of the properties, several stand out as particular challenges to any theoretical effort. (i) The contrast between the diversity and changeability of conscious states and the unitary appearance to the conscious individual of each conscious state. This unity requires the binding together of diverse sensory modalities that show constructive features such as those seen in Gestalt phenomena. (ii) The property of intentionality. This term refers to the fact that consciousness is generally, but not always, about objects or events. At the same time, consciousness is modulated by attention and has wide access to memory and imagery. (iii) Subjective feelings or qualia; the experiencing, for example, of the redness of red, the warmness of warmth. This is put pointedly by Nagel's phrase: "What is it like to be a bat?" or, as he implies, any other conscious being.

3) Can we construct a neural framework to account for such a wide range of properties? The author believes that present advances in neuroscience permit us to do so, provided that we take into account some constraints based on experimental observations. These suggest that consciousness is not a property of a single brain location or neuronal type, but rather is the result of dynamic interactions among widely distributed groups of neurons. A major system that is essential for conscious activity is the thalamocortical system. The integrative dynamics of conscious experience suggest that the thalamocortical system behaves as a "functional cluster"; that is, it interacts mainly with itself. Nevertheless, it also interacts with other brain systems. For example, interactions between the basal ganglia and the thalamocortical system are likely to influence the modulation of consciousness by attention as well as the development of automaticity through learning. The threshold of activity in these neural structures is governed by diffuse ascending value systems, such as the mesencephalic reticular activating system interacting with the intralaminar nuclei of the thalamus, as well as noradrenergic, serotonergic, cholinergic, and dopaminergic nuclei.

4) In summary: Consciousness has a number of apparently disparate properties, some of which seem to be highly complex and even inaccessible to outside observation. To place these properties within a biological framework requires a theory based on a set of evolutionary and developmental principles. The author describes such a theory, which aims to provide a unifying account of conscious phenomena.

References (abridged):

1. Descartes, R. (1975) in The Philosophical Works of Descartes, eds. Haldane, E. & Ross, G. (Cambridge Univ. Press, Cambridge, U.K.), Vol. 1 and 2

2. Popper, K. & Eccles, J. F. (1977) The Self and Its Brain (Springer, New York)

3. Penrose, R. (1994) Shadows of the Mind: A Search for the Missing Science of Consciousness (Oxford Univ. Press, New York)

4. McGinn, C. (1991) The Problem of Consciousness: Essays Toward a Resolution (Blackwell, Oxford)

5. Metzinger, T., ed. (2000) Neural Correlates of Consciousness: Empirical and Conceptual Questions (MIT Press, Cambridge, MA)

Proc. Nat. Acad. Sci. http://www.pnas.org

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COGNITIVE SCIENCES: ON CONSCIOUSNESS

The following points are made by E. Roy John (Brain Research Revs. 2002 39:1):

1) Consciousness combines information about attributes of the present multimodal sensory environment with relevant elements of information about the past. Information from each modality is continuously fractionated into distinct features, processed locally by different brain regions relatively specialized for extracting these disparate components, and processed globally by interactions among these regions.

2) Information in the brain is represented by levels of synchronization within neuronal populations, and by levels of coherence among multiple brain regions that deviate from random fluctuations. Significant deviations constitute local and global "negative entropy", or information. Local electric field potentials reflect the degree of synchronization among the neurons of the local ensembles.

3) The author proposes that large-scale integration, or "binding", involves oscillations of local electric field potentials that play an important role in facilitating synchronization and coherence. The binding is assessed by neuronal coincidence detectors, and parsed into perceptual frames by cortico-thalamo-cortical loops.

4) The most probable baseline levels of local synchrony, coherent interactions among brain regions, and perceptual time-frame durations, have been quantitatively described in large studies of their age-appropriate normative distributions, and are considered by the author as an approximation to a conscious "ground state".

5) The level of consciousness during anesthesia can be accurately predicted by the magnitude and direction of reversible multivariate deviations from this ground state. An invariant set of changes takes place during anesthesia, independent of the particular anesthetic agent.

6) The author suggests that evidence from a variety of neuroscience areas supporting the propositions of the author. These propositions, together with the invariant reversible electrophysiological changes observed with loss and return of consciousness, provide a foundation for a theory of consciousness.

7) The author emphasizes the need to consider global as well as local processes in the search for better explanations of how the brain accomplishes the transformation from synchronous and distributed neuronal discharges to seamless global subjective awareness.(1-5)

References (abridged):

1. P. Ackermann and A.A. Borbely , Coherence analysis of the human sleep electroencephalogram. Neuroscience 85 (1998), pp. 1195?x2013;1208

2. H. Ahn, L.S. Prichep, E.R. John, H. Baird, M. Trepetin and H. Kaye , Developmental equations reflect brain dysfunction. Science 210 (1980), pp. 1259-1262

3. M.T. Alkire, R.J. Haier and J.H. Fallon , Toward the neurobiology of consciousness: using brain imaging and anesthesia to investigate the anatomy of consciousness. In: S.R. Hameroff, A. Kaszriak and A. Scott, Editors, Toward A Science of Consciousness II; The Second Tucson Discussions and Debates, MIT Press, Cambridge (1998), pp. 255-268

4. M.T. Alkire, R.J. Haier and J.H. Fallon , Toward a unified theory of narcosis: brain imaging evidence for a thalamocortical switch as the neurophysiologic basis of anesthesia-induced unconsciousness. Conscious. Cogn. 9 (2000), pp. 370?x2013;386

5. D.A. Allport , Phenomenal simultaneity and perceptual moment hypotheses. Br. J. Psychol. 59 (1968), pp. 395-406

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