To the never-ending battles between science versus creationism, unidentified flying objects, extrasensory perception, ectoplasm, and the like, we now have to add the perpetual battle over human stem cell research. Where should the line be drawn? I have received a personal communication that spermatozoa are human, or at least half human, and should therefore be treated, as such, with appropriate respect. This notion has, understandably, been a source of great embarrassment to certain males of the population. Along the same vein, there is a hue and cry about how, each month, when an egg doesn't get fertilized, there is the potential loss of a life.

     Where to draw the line? One can get stem cells from embryos, or less flexible “stem” cells from infants or adults. In the present essay it is argued that there is a simple and non-controversial test: If the cell is conscious, or part of a conscious ensemble, such as a brain cell, it is human and must not be tampered with. This should be non-controversial because, after hundreds of papers written on the subject, including many books, nobody can explain consciousness. It is easy enough to define consciousness – “The state of having an awareness of one’s own existence, sensations, and thoughts, and of one’s environment” – but this does not explain why we have an “awareness of being.”  One of the purposes of this essay is to give a minuscule review of what we know about consciousness. 

     I am under no illusion that bioethicists will pay the slightest attention to consciousness as a dividing line between stem cell experiments and a scientifically-based taboo, but one cannot legislate-away stem cell (and cloning) research, because anybody with a microscope and steady hand can get into the business. Eventually, perhaps many years from now, even the bootleggers working in their basements, and who sell body parts, will stop at conscious brain tissue.  

     Cloning another human would be a great scientific achievement. Imagine – instead of growing up with an identical brother (or sister), which is socially acceptable, I could watch my identical “son” (or “daughter”) grow up. Why does society gasp in horror if 100% of his DNA is like mine, rather than 99.9%? Some of the objectors claim that we are usurping the work of the “Deity.” From where I sit, the main job of the Deity is to oversee the destruction of as many humans as possible via endless religious wars.

     About half of the literature on consciousness does explain it with various references to some kind of deity and/or paranormal extra-sensory perception, but these pseudoscientific arguments cannot survive the test of time. The scientific literature reveals that the brain contains very approximately 75 compartments, and we have made tremendous strides in discovering the type of data that each compartment handles (such as visual, auditory, muscle coordination, and so forth).

      The “easy” part of consciousness research is to discover how the brain functions [1],[2],[3],[4],[5],[6]. This is “easy” in the sense that, after we completely know the circuitry of the brain, and every signal that accompanies every sensory input and every “thought” and every motor output, we can never answer the basic question: “Is the red that you see the same as the red that I see?”

     Nevertheless, let’s take a short excursion into solving the “easy” problems. First, determine the function of each volume of the brain; second, trace the neuronal circuits; third, represent the neuronal circuits in the form of a circuit diagram; fourth, achieve maximum simplification by summarizing the above via a block diagram. Each of these aspects of brain research is illustrated, below, by means of a pertinent diagram. 

     First, Fig. 1 (Figs. 1 to 6 are taken from [7]) depicts an approximate cross section of the human brain. Seventeen of the most important regions, plus the spinal cord, are labeled, but an anatomy book will show that names have been assigned to many additional volumes of the brain. 

Fig. 1- Approximate cross-section of the human brain, with some regions in dashed lines for the sake of clarity. Seventeen of the most important regions are labeled, plus the spinal cord.

     Second, the tracing of neuronal circuits is illustrated, in Fig. 2, for the cerebellar cortex. (This is the outside layer of the cerebellum of Fig. 1.) At first glance this seems to be a “hopeless mess,” but with a reasonable amount of patience (and a magnifying glass, perhaps) one can extract the main features of the cerebellar cortex. But the hardest part is yet to surface – one must determine whether each junction is excitatory (E) or inhibitory (I).

Fig. 2- A three-dimensional view of the cerebellar cortex as provided by three mutually perpendicular cuts. Parallel to the front cut we have dendrites of the Purkinje, basket, and stellate cells. The following are mutually perpendicular: (1)Purkinje cell dendrites; (2)parallel fibers; and (3)basket and stellate cell axons. The Golgi cell dendrites have a cylindrical architecture, like a conventional tree. [8]. 

    Third, having deciphered each portion of the neuronal circuit, and the E and I of every junction, one can draw an electrical schematic, as shown in Fig. 3. Here, also, the hardest part is yet to surface – because the brain is three-dimensional, one must draw a three-dimensional network. (This is reminiscent of the DNA models that gave birth to three-dimensional laboratory and teaching accessories.)

     

Fig. 3- Hypothetical model of the basic neural network of the cerebellar cortex. It is useless to analyze this circuit as shown, however, because the cerebellum must be analyzed as a three-dimensional network.

     Fourth, on an even higher intellectual level that is not concerned with the three-dimensional aspects of a network, are the block diagrams of Figs. 4 and 5. These are highly conjectural summaries of brain activity. Figure 4 shows the mechanisms of memory while Fig. 5 is an even more ambitious depiction of a simple brain that can read and write.

Fig. 4- Hypothetical block diagram that attempts to summarize the mechanisms of memory.

Fig. 5- Hypothetical block diagram of a relatively simple brain that can read and tell us what it is reading in the upper half of the diagram; listen to a conversation and write down what it hears in the lower half.

     Before you dismiss Figs. 4 and 5 as worthless conjecture, however, you should try to answer the following question: Which portions of the block diagram are inside, and part of, the consciousness “platform”? In other words, what portions can be deleted (or surgically removed), which will remove sensory inputs and motor outputs, while still leaving the patient “fully conscious”? One can gain considerable insight into this from the many people, each day, who are partially disabled by a stroke.  
 
     Nevertheless, we remain very far from knowing all of the secrets of pattern recognition, memory storage, and retrieval. In the limit, we will trace every nerve axon in a typical brain, and the dendritic inputs to every axon, and its synaptic junction outputs. This feat is far more difficult than the sequencing of a mere 3 billion base pairs of a typical human DNA. The complete three-dimensional mapping of the brain will be a revolutionary accomplishment that is many years off into the future. We will discover that your nerve signals are pretty much the same as mine when we see "red." But is your subjective red the same as mine? We will never know the answer to that one. 

     One must be careful here with definitions. If you are UN-conscious, it may be perfectly ethical for one of those biopsy-wielding monsters to sneak up on you and extract a few stem cells. In my own case, after 10 minutes into any lecture that I ever attended, I lost an awareness of being, and became a candidate for stem-cell research (or, hopefully, cloning). 

     But there is a greater danger here. Just as we cannot explain consciousness, you cannot prove that you are conscious! The proof of that statement is simple: Suppose that we build a machine (or a computer program, at least) that has a brain. It includes a random-noise generator so that, via serendipity, when a “viable” set of signals comes along, the brain says something that is creative and that makes sense. For example, toss 10 coins into the air; on average, on one out of 1024 throws, all of the coins will land heads up. This is also how it is with human creativity. Because of the random signal generator, the computer brain is unpredictable; it does not, of course, have “free will.” It goes without saying that it has a memory, and stores (learns) all of those nuggets of creativity. The point that I am getting at is this: Ask the brain if it has a consciousness: If it says “Yes, I am conscious,” you say that it is lying because it is only a computer program. But exactly the same argument applies to you, dear reader. I ask you if you are conscious: If you say “No,” you get a biopsy zap; if you say “Yes,” I say “How do I know that you are not lying?” 

     There certainly is a contradiction here. How can one determine if a volume of tissue is conscious or unconscious? Generation of a particular pattern of chemical or electrical activity does not guarantee consciousness. A minimum requirement for consciousness, however, is that the cell, or group of cells, be  part of a "brain." They can be in the form of a clever computer program, or a robot that occasionally says something noteworthy, or even an awake human. But problems remain because the definition of consciousness is rather vague. 

     The Animal Kingdom emerged, approximately, one billion years ago. Animals move about from place to place in search of food, to escape from predators, find a mate, and so forth. Movement requires a nervous system, and the integration of movement requires a brain. It is appropriate to ask, then, do insects have a consciousness, an awareness of being? If a bee sees a red flower, is it the same red that I see? Is pain the same to a bee, or to you and me? Because these questions can never be answered, it appears that consciousness will forever be beyond the reach of the human brain. 

     It doesn’t take much to give an impression of intelligent behavior (and I am not thinking of the U.S. members of Congress here): Get a microscope and look at a drop of muddy water taken from a bowl that holds plant stems. You will see a myriad of tiny cells scurrying about exactly like office workers, during lunch time, in Times Square. None of them have a nervous system, of course; they are merely responding to chemical signals (like office workers during lunch time!). 

     But let’s not muddy the water with talk about paramecia and insects; let’s stick to humans. At what point in embryonic development does consciousness begin? As directed by its DNA molecule, given the proper raw materials, the fertilized egg starts to synthesize amino acids and proteins. At first, it starts to grow by dividing repeatedly in two: 1, 2, 4, 8, … cells. Eventually, a “neural plate” forms, cells proliferate in localized regions, the immature neurons migrate to their final residences [9], they aggregate and differentiate to form the various parts of the brain, they mature and form connections with other neurons. Starting with almost nothing, with a few simple building blocks, a brain is thus created. Somewhere along the way, probably after birth when a certain minimum number of connections have been completed, the human infant becomes aware that it exists. Eventually, it learns that it has a unique identity, and it acquires an illusion of free will.

     There is no “threshold of consciousness.” Scalp electrodes show that electroencephalographic (EEG) signal spectra gradually change from the prenatal period to the beginning of adulthood.

     Consciousness resides in a Consciousness Platform (CP) upon which sensory inputs, "thought" signal patterns, and outputs (such as motor commands) interact. The CP is reserved for a select few of the body’s nerve signals. We are not aware of the goings-on in the involuntary, visceral, autonomic nervous systems (housekeeping chores for the most part, such as digestion and heart beat). These modalities would only distract the conscious brain; it has to concentrate on one situation at a time (hence the obvious “discovery” that driving, while paying attention to a cell phone, can be dangerous). A myriad number of experiments are performed on the visual, auditory, and other sensory systems of an intact animal while it is unconscious -- that is, the nerve discharges in its CP have been immobilized via anesthesia. And vice versa: the human experience is that an awake CP gets a blank visual input if, for example, you close your eyes.  

     Sometimes, in patients desperately ill with recurrent epileptic seizures, the commissure is cut surgically in order to open the feedback path that is responsible for the oscillations. This is known as “split brain” surgery. Actually, it is not possible to completely split the brain because one would have to cut through vital neurons in the central structures Aside from benefit to the patient, the split brain is interesting because it is possible for an experimenter to feed conflicting information into each hemisphere. Normally, each hemisphere knows what information the other is receiving because of the commissure fibers (although there is a great deal of duplication, the two hemispheres are far from identical). In the case of a split-brain patient who is receiving conflicting signals, the dominant hemisphere “decides” that its information is the true state of affairs, and it suppresses the recessive hemisphere. (If a person is right-handed, the left hemisphere is dominant in most of the dual-choice situations, and vice versa.)

     Another problem is that consciousness is fragile. Here is an amazing, painless experiment that you can do to yourself in a few minutes: Borrow a dime and, on a sheet of white paper, use it to draw two circles around 2 ¼-inch (5.8 cm) apart. In one circle draw a +, in the other an x, as in Fig. 6. Then stare at the two circles, but let your gaze look beyond so that the two circles coincide. Almost immediately, you will lose the +, or the x, or bits and pieces of the + and x. In this binocular rivalry, the visual system cannot tolerate conflicting information, so it deletes the input of an entire eye before it reaches your CP! 

Fig. 6- Visual stimulus used to demonstrate the “blocking out of reality.” Stare at the two circles, but let your gaze look beyond so that the two circles coincide. Almost immediately you will lose the +, or the x, or bits and pieces of the + and x. This is an example of binocular rivalry.
   
     Finally, another example of fragility is the ease with which one can doze off at a lecture. It is usually a painless way to die. (In my own case, my fellow students always thought it was more fun to let me die with an audible accompaniment.) Although one may regard sleep as a “waste of time,” it is probably used to restore the chemical environment that has deteriorated after hours devoted to excitation and inhibition. But because sleep is essential, evolution has never figured out a way to avoid sleep, despite the accompanying frequent and sometimes dangerous loss of consciousness. 

     To conclude: The debate over human stem cell research is tied in with a creationist philosophy which says that a group of human cells has a soul; it will never end. From a scientific point of view, however, even brain tissue regenerates, and one can "pick a brain" to get stem cells. Nevertheless, in this essay, it is suggested that the line should be drawn at tissue that is conscious, defined as best we can, with all of its pitfalls and problems.

     [1] Stevan Harnad, “No Easy Way Out,” The Sciences, Spring 2001.
     [2] Antonio Damasio, The Feeling of What Happens, Harcourt Brace, 1999.
     [3] Gerald M. Edelman & Giulio Tononi, A Universe of Consciousness, Basic Books, 2000.
     [4] Colin McGinn, The Mysterious Flame, Basic Books, 1999.
     [5] Michael Tomasello, The Cultural Origins of Human Cognition, Harvard Univ Press, 1999.
     [6] Jerry Fodor, “The Mind Doesn’t Work That Way,” MIT Press, 2000.
     [7] Sid Deutsch & Alice Deutsch, Understanding the Nervous System, IEEE Press, 1993.
     [8] David Marr, “A Theory of Cerebellar Cortex,” J. Physiol., vol 202, 1969.
     [9] Mary E. Hatten, “New Directions in Neuronal Migration,” Science, 6 Sep 2002.                                                                          
 

*Published in a shorter version in IEEE Engineering in Medicine and Biology Magazine, July/Aug 2002.