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others in life sciences: How does the set of processes we call mind emerge from the activity of the organ we call brain? The question is hardly new. It has been formulated in one way or another for centuries. Once it became possible to pose the ques- tion and not be burned at the stake, it has been asked openly and insistently. Recently the question has preoccupied both the experts—neuroscientists, cognitive scientists and philoso- phers—and others who wonder about the origin of the mind, specifically the conscious mind. The question of consciousness now occupies center stage because biology in general and neuroscience in particular have been so remarkably successful at unraveling a great many of life’s secrets. More may have been learned about the brain and the mind in the 1990s—the so-called decade of the brain—than during the entire previous history of psychology and neuro- science. Elucidating the neurobiological basis of the conscious mind—a version of the classic mind-body problem—has be- come almost a residual challenge. Contemplation of the mind may induce timidity in the con- templator, especially when consciousness becomes the focus of the inquiry. Some thinkers, expert and amateur alike, believe the question may be unanswerable in principle. For others, the relentless and exponential increase in new knowledge may give rise to a vertiginous feeling that no problem can resist the as- sault of science if only the theory is right and the techniques are powerful enough. The debate is intriguing and even unexpect- ed, as no comparable doubts have been raised over the likeli- hood of explaining how the brain is responsible for processes such as vision or memory, which are obvious components of the larger process of the conscious mind. I am firmly in the confident camp: a substantial explanation for the mind’s emergence from the brain will be produced and perhaps soon. The giddy feeling, however, is tempered by the acknowledgment of some sobering difficulties. Nothing is more familiar than the mind. Yet the pilgrim in search of the sources and mechanisms behind the mind em- barks on a journey into a strange and exotic landscape. In no particular order, what follows are the main problems facing those who seek the biological basis for the conscious mind. The first quandary involves the perspective one must adopt to study the conscious mind in relation to the brain in which we believe it originates. Anyone’s body and brain are observable to third parties; the mind, though, is observable only to its own- er. Multiple individuals confronted with the same body or brain can make the same observations of that body or brain, but no comparable direct third-person observation is possible for any- one’s mind. The body and its brain are public, exposed, exter- nal and unequivocally objective entities. The mind is a private, hidden, internal, unequivocally subjective entity. How and where then does the dependence of a first-person mind on a third-person body occur precisely? Techniques used to study the brain include refined brain scans and the measure- ment of patterns of activity in the brain’s neurons. The naysay- ers argue that the exhaustive compilation of all these data adds up to correlates of mental states but nothing resembling an ac- tual mental state. For them, detailed observation of living mat- ter thus leads not to mind but simply to the details of living mat- 4 S C I E N T I F I C A M E R I C A N U p d a t e d f r o m t h e D e c e m b e r 1 9 9 9 i s s u e SL IM F IL M S MULTIMEDIA MIND-SHOW occurs constantly as the brain processes external and internal sensory events. As the brain answers the unasked question of who is experiencing the mind-show, the sense of self emerges. Brain How the We have long wondered how the conscious mind comes to be. Greater understanding of brain function ought to lead to an eventual solution At the start of the new millennium, it is apparent that one question towers above all By Antonio R. Damasio theMind Creates COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. ter. The understanding of how living mat- ter generates the sense of self that is the hallmark of a conscious mind—the sense that the images in my mind are mine and are formed in my perspective—is simply not possible. This argument, though in- correct, tends to silence most hopeful in- vestigators of the conscious mind. To the pessimists, the conscious-mind problem seems so intractable that it is not even possible to explain why the mind is even about something—why mental pro- cesses represent internal states or interac- tions with external objects. (Philosophers refer to this representational quality of the mind with the confusing term “intention- ality.”) This argument is false. The final negative contention is the re- minder that elucidating the emergence of the conscious mind depends on the exis- tence of that same conscious mind. Con- ducting an investigation with the very in- strument being investigated makes both the definition of the problem and the ap- proach to a solution especially compli- cated. Given the conflict between observ- er and observed, we are told, the human intellect is unlikely to be up to the task of comprehending how mind emerges from brain. This conflict is real, but the notion that it is insurmountable is inaccurate. In summary, the apparent uniqueness of the conscious-mind problem and the difficulties that complicate ways to get at that problem generate two effects: they frustrate those researchers committed to finding a solution and confirm the con- viction of others who intuitively believe that a solution is beyond our reach. Evaluating the Difficulties THOSE WHO CITE the inability of re- search on the living matter of the brain to reveal the “substance of mind” assume that the current knowledge of that living matter is sufficient to make such judg- ment final. This notion is entirely unac- ceptable. The current description of neu- robiological phenomena is quite incom- plete, any way you slice it. We have yet to resolve numerous details about the func- tion of neurons and circuits at the molec- ular level; we do not yet grasp the behav- ior of populations of neurons within a lo- cal brain region; and our understanding of the large-scale systems made up of mul- tiple brain regions is also incomplete. We are barely beginning to address the fact that interactions among many noncon- tiguous brain regions probably yield high- ly complex biological states that are vast- ly more than the sum of their parts. In fact, the explanation of the physics related to biological events is still incom- plete. Consequently, declaring the con- scious-mind problem insoluble because we have studied the brain to the hilt and have not found the mind is ludicrous. We have not yet fully studied either neurobi- ology or its related physics. For example, at the finest level of description of mind, the swift construction, manipulation and superposition of many sensory images might require explanation at the quantum level. Incidentally, the notion of a possi- ble role for quantum physics in the eluci- dation of mind, an idea usually associat- ed with mathematical physicist Roger Penrose of the University of Oxford, is not an endorsement of his specific pro- posals, namely that consciousness is based on quantum-level phenomena oc- curring in the microtubules—constituents of neurons and other cells. The quantum level of operations might help explain how we have a mind, but I regard it as un- necessary to explain how we know that we own that mind—the issue I regard as most critical for a comprehensive account of consciousness. The strangeness of the conscious- mind problem mostly reflects ignorance, which limits the imagination and has the curious effect of making the possible seem impossible. Science-fiction writer Arthur C. Clarke has said, “Any suffi- ciently advanced technology is indistin- guishable from magic.” The “technolo- gy” of the brain is so complex as to ap- pear magical, or at least unknowable. The appearance of a gulf between mental states and physical/biological phenomena comes from the large disparity between two bodies of knowledge—the good un- derstanding of mind we have achieved through centuries of introspection and the efforts of cognitive science versus the in- complete neural specification we have achieved through the efforts of neuro- science. But there is no reason to expect that neurobiology cannot bridge the gulf. Nothing indicates that we have reached the edge of an abyss that would separate, DI M IT R Y SC H ID LO VS K Y; S O U R C E : TO O TE LL E T AL ., I N JO U R N AL O F N EU R O SC IE N C E, M AY 1 9 8 8 ( le ft ); H AN N A D AM AS IO ( a b ov e a n d o p p os it e p a g e) 6 S C I E N T I F I C A M E R I C A N T H E H I D D E N M I N D BRAIN’S BUSINESS is representing other things. Studies with macaques show a remarkable fidelity between a seen shape (a) and the shape of the neural activity pattern (b) in one of the layers of the primary visual cortex. NEUROSCIENCE continues to associate specific brain structures with specific tasks. Some language regions are highlighted in a and b. Color-processing (red) and face-processing (green) regions are shown in c. One’s own body sense depends on the region shown in d. a a b COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. in principle, the mental from the neural. Therefore, I contend that the biologi- cal processes now presumed to corre- spond to mind processes in fact are mind processes and will be seen to be so when understood in sufficient detail. I am not denying the existence of the mind or say- ing that once we know what we need to know about biology the mind ceases to exist. I simply believe that the private, per- sonal mind, precious and unique, indeed is biological and will one day be described in terms both biological and mental. The other main objection to an un- derstanding of mind is that the real con- flict between observer and observed makes the human intellect unfit to study itself. It is important, however, to point out that the brain and mind are not a monolith: they have multiple structural levels, and the highest of those levels cre- ates instruments that permit the observa- tion of the other levels. For example, lan- guage endowed the mind with the power to categorize and manipulate knowledge according to logical principles, and that helps us classify observations as true or false. We should be modest about the likelihood of ever observing our entire na- ture. But declaring defeat before we even make the attempt defies Aristotle’s obser- vation that human beings are infinitely curious about their own nature. Reasons for Optimism MY PROPOSAL for a solution to the co- nundrum of the conscious mind requires breaking the problem into two parts. The first concern is how we generate what I call a “movie-in-the-brain.” This “movie” is a metaphor for the integrated and uni- fied composite of diverse sensory im- ages—visual, auditory, tactile, olfactory and others—that constitutes the multi- media show we call mind. The second is- sue is the “self” and how we automati- cally generate a sense of ownership for the movie-in-the-brain. The two parts of the problem are related, with the latter nest- ed in the former. Separating them is a use- ful research strategy, as each requires its own solution. Neuroscientists have been attempting unwittingly to solve the movie-in-the- brain part of the conscious-mind problem for most of the history of the field. The en- deavor of mapping the brain regions in- volved in constructing the movie began almost a century and a half ago, when Paul Broca and Carl Wernicke first sug- gested that different regions of the brain were involved in processing different as- pects of language. More recently, thanks to the advent of ever more sophisticated tools, the effort has begun to reap hand- some rewards. Researchers can now directly record the activity of a single neuron or group of neurons and relate that activity to aspects of a specific mental state, such as the per- ception of the color red or of a curved line. Brain-imaging techniques such as PET (positron emission tomography) scans and fMR (functional magnetic res- onance) scans reveal how different brain regions in a normal, living person are en- gaged by a certain mental effort, such as relating a word to an object or learning a particular face. Investigators can deter- mine how molecules within microscopic neuron circuits participate in such diverse mental tasks, and they can identify the genes necessary for the production and deployment of those molecules. Progress in this field has been swift ever since David H. Hubel and Torsten Wiesel of Harvard University provided the first clue for how brain circuits repre- sent the shape of a given object, by demonstrating that neurons in the prima- ry visual cortex were selectively tuned to respond to edges oriented in varied an- gles. Hubel and Margaret S. Livingstone, also at Harvard, later showed that other neurons in the primary visual cortex re- spond selectively to color but not shape. And Semir Zeki of University College London found that brain regions that re- ceived sensory information after the pri- mary visual cortex did were specialized for the further processing of color or movement. These results provided a coun- terpart to observations made in living neu- rological patients: damage to distinct re- gions of the visual cortices interferes with color perception while leaving discern- ment of shape and movement intact. A large body of work, in fact, now points to the existence of a correspon- w w w . s c i a m . c o m T H E H I D D E N M I N D 7 ANTONIO R. DAMASIO is M. W. Van Allen Distinguished Professor and head of the department of neurology at the University of Iowa College of Medicine and adjunct professor at the Salk Institute for Biological Studies in San Diego. He was born in Portugal and received his M.D. and Ph.D. from the University of Lisbon. With his wife, Hanna, Damasio created a facility at Iowa dedicated to the investigation of neurological disorders of mind and behavior. A mem- ber of the Institute of Medicine of the National Academy of Sciences and of the American Academy of Arts and Sciences, Damasio is the author of Descartes’ Error: Emotion, Reason, and the Human Brain (1994), The Feeling of What Happens: Body and Emotion in the Mak- ing of Consciousness (1999) and Looking for Spinoza (forthcoming). TH E A U TH O R b c d COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. 8 S C I E N T I F I C A M E R I C A N T H E H I D D E N M I N D dence between the structure of an object as taken in by the eye and the pattern of neuron activity generated within the vi- sual cortex of the organism seeing that object [see illustration on page 6]. Further remarkable progress involv- ing aspects of the movie-in-the-brain has led to increased insights related to mech- anisms of learning and memory. In rapid succession, research has revealed that the brain uses discrete systems for different types of learning. The basal ganglia and cerebellum are critical for the acquisition of skills—for example, learning to ride a bicycle or play a musical instrument. The hippocampus is integral to the learning of facts pertaining to such entities as people, places or events. And once facts are learned, the long-term memory of those facts relies on multicomponent brain sys- tems, whose key parts are located in the vast brain expanses known as cerebral cortices. Moreover, the process by which new- ly learned facts are consolidated in long- term memory goes beyond properly work- ing hippocampi and cerebral cortices. Certain processes must take place, at the level of neurons and molecules, so that the neural circuits are etched, so to speak, with the impressions of a newly learned fact. This etching depends on strengthen- ing or weakening the contacts between neurons, known as synapses. A provoca- tive finding by Eric R. Kandel of Colum- bia University and Timothy P. Tully of Cold Spring Harbor Laboratory is that etching the impression requires the syn- thesis of fresh proteins, which in turn re- lies on the engagement of specific genes within the neurons charged with sup- porting the consolidated memory. These brief illustrations of progress could be expanded with other revelations from the study of language, emotion and decision making. Whatever mental func- tion we consider, it is possible to identify distinct parts of the brain that contribute to the production of a function by work- ing in concert; a close correspondence ex- ists between the appearance of a mental state or behavior and the activity of se- lected brain regions. And that correspon- dence can be established between a given macroscopically identifiable region (for example, the primary visual cortex, a lan- guage-related area or an emotion-related nucleus) and the microscopic neuron cir- cuits that constitute the region. Most exciting is that these impressive advances in the study of the brain are a mere beginning. New analytical tech- niques continuously improve the ability to study neural function at the molecular level and to investigate the highly com- plex large-scale phenomena arising from the whole brain. Revelations from those two areas will make possible ever finer correspondences between brain states and mental states, between brain and mind. As technology develops and the ingenuity of researchers grows, the fine grain of physical structures and biological activi- ties that constitute the movie-in-the-brain will gradually come into focus. Confronting the Self THE MOMENTUM of current research on cognitive neuroscience, and the sheer accumulation of powerful facts, may well convince many doubters that the neural basis for the movie-in-the-brain can be identified. But the skeptics will still find it difficult to accept that the second part of the conscious-mind problem—the emer- gence of a sense of self—can be solved at all. Although I grant that solving this part of the problem is by no means obvious, a possible solution has been proposed, and a hypothesis is being tested. The main ideas behind the hypothesis involve the unique representational abil- ity of the brain. Cells in the kidney or liv- er perform their assigned functional roles and do not represent any other cells or functions. But brain cells, at every level of the nervous system, represent entities or events occurring elsewhere in the organ- ism. Brain cells are assigned by design to be about other things and other doings. They are born cartographers of the geog- raphy of an organism and of the events that take place within that geography. The oft-quoted mystery of the “inten- tional” mind relative to the representa- tion of external objects turns out to be no mystery at all. The philosophical despair that surrounds this “intentionality” hur- dle alluded to earlier—why mental states represent internal emotions or interac- tions with external objects—lifts with the consideration of the brain in a Darwinian context: evolution has crafted a brain that is in the business of directly representing the organism and indirectly representing whatever the organism interacts with. The brain’s natural intentionality then takes us to another established fact: the brain possesses devices within its struc- ture that are designed to manage the life of the organism in such a way that the in- ternal chemical balances indispensable for survival are maintained at all times. These devices are neither hypothetical nor ab- stract; they are located in the brain’s core, the brain stem and hypothalamus. The brain devices that regulate life also repre- sent, of necessity, the constantly changing states of the organism as they