jueves, 17 de diciembre de 2009

Expanding the Human Mind: The Future of the Brain: Neurobiology, Electronics, and Other Tools Part 1

by William Holmes

We have the power to enhance our minds by three very different approaches: by education, by computers, and by the techniques of neurobiology. While education dates back to prehistoric times, computers are a modern invention barely a half century old. Neurobiology is only now beginning to realize its potential for expanding our minds.
Education has gradually become a formal process for passing on knowledge as cultures have grown more complex and opportunities for adults have multiplied. Education is still our best hope for productive, prosperous individuals and nations, but the speed and learning capacity of the human mind is reaching its limits. Formal education and training for doctors, lawyers, and Ph.D.'s takes up to 20 years.

Computers provide one path toward overcoming the speed and capacity limitations of the human mind. The programmed electronic computer was first conceived as a successor to mechanical calculators, then adapted to record keeping in the business world. It was soon apparent that any mental task reducible to a set of written rules can be reduced to a computer program. This realization has led to continuing optimism that practically any task the mind performs can be analyzed in detail and programmed. The remarkable technical achievements of the electronic industry in doubling computer capacity and speed at the same cost every two or three years has fueled this optimism. If the problem is too difficult to solve today, more computer power will surely come to the rescue before long.

One should not belittle the accomplishments of computer programs. Inexpensive computers with quality graphics will bring universal education and specialized training to even the most impoverished countries. Their schools will need little more than electric generators for the computers and local teachers for guidance. A world of less formal information is at our fingertips through the Internet, fostering all kinds of informal self-education. Practically all records are on computers, and one can increasingly pose simple questions in natural language and hope to receive a useful response. There are "expert programs" for solving a large range of specialized problems, from the best mix of crops for the family farm to the material requirements and assembly instructions for building a house. Computers with TV cameras are learning to recognize faces and common objects by sight. Adding mechanized appendages to a computer lets it grasp, recognize, and manipulate objects, and to move through a cluttered environment. Even simple forms of true robots are appearing, with facial expressions and simulated emotions.
Some prognosticators have extrapolated the steady advance of intellectual and robotlike computer programs to the extreme, predicting computers of superhuman mental powers along with superhuman speed. These predictions rely on extrapolating the past and present exponential increase in computer power for decades into the future. Such predictions also assume that the hard, unsolved problems of understanding how the human mind works will rapidly yield to sustained effort.
But even if computers do become comparable to humans for performing common intellectual and physical tasks, they will still be outsiders. We will have created independent creatures with minds of sorts, but no more a part of ourselves than the aliens of science fiction. Such computers/robots will at best be capable assistants. We must look inward in order to enhance our own minds and explore their potential. We need the science and techniques of biology, more specifically human neurobiology.

Advancing the Power of the Mind
Neurobiology is the science of the nervous system, and it can be approached from many directions. Neuroanatomy studies the physical structure of the brain and how brain cells (neurons) are organized and connected. The connections themselves are quite complex. Electric pulses from a neuron travel down a branching axon fiber to destinations on other neurons. The ends of the fibers secrete nanosize packets of neurotransmitters that bind to receptors on the destination neuron, either stimulating or inhibiting it. Thousands of axons from other neurons may impinge on a single neuron, each capable of secreting neurotransmitter packets. The neurotransmitters combine to cause the neuron to either generate electric pulses or suppress them. Neurotransmitters may also interact in more complex ways, providing the neuron much flexibility in response to its many inputs.

Unraveling the complexities of neurotransmitters is a major focus of neurobiology research. It is the foundation for the rational design of medicines for treating depression, mania, schizophrenia, Parkinson's disease, and other mental and physical disorders of the brain. In brief, current medicines interact with specific neurotransmitter receptors on certain classes of neurons, altering the effects of a natural deficiency or excess in neurotransmitter action.

Over the past 150 years we have accumulated a significant body of knowledge relating higher brain functions, such as language, to specific areas of the brain. Much of this knowledge has come from observing individuals with brain damage, using magnetic resonance imaging (MRI) or in some cases autopsies. Many strange deficits have been observed, such as inability to recognize spoken words, the loss of color vision, loss of the sense of humor, and the inability to visualize or draw one side of the body.

Today we can even peer inside the human brain to some degree, primarily by functional MRI, which allows researchers to observe those areas of the brain that become more active while performing such ordinary activities as reading or solving simple problems. The most detailed view of all comes from electrodes placed in the brain to measure the activity of individual neurons. Though largely limited to primate brain research, we have found such astonishing entities as "mirror neurons." These neurons respond to an action such as grasping an object both when the subject does the grasping and when the subject sees another individual grasping the object. We are watching some innate capacity of the brain to imitate the action of others. Unfortunately, researchers' inability to instruct nonhuman test subjects--or to question them about their mental states--limits these studies' potential for applying the findings to humans. So we must fall back on the methods of experimental animal psychology to pose the problem and analyze the results.

It is awesome to contemplate the full complexity of the brain, tens of billions of neurons connected through literally trillions of branches acting through complex patterns of neurotransmitters. It will take many decades to learn in detail how activities at the neurotransmitter level result in the conscious activities we experience and the subconscious activities we can measure by electrodes, MRI, and other methods.

In this light, proposals to simulate the entire brain in molecular detail on a computer seem presumptuous. Proponents believe that such a simulation will produce a functioning inorganic brain. Presumably these simulations will produce numerous high-speed geniuses to simultaneously work on our most difficult problems.

A Piece of Your Mind?
Clearly, we must study in great detail the characteristics of individual neurons. The cell is the fundamental structural and functional unit of biological organisms. Thus, studies of the brain and the rest of the nervous system ultimately depend on our knowledge of its neurons. Can they be classified into a reasonable number of types? What is the molecular biology of each type, its neurotransmitters, receptors, pattern of axon branching, modes of modification, and propensity for growth?

With this information, we could identify specific neuron cell types within the brain, recording their locations and connections to other neurons. It should also become possible to isolate neuron stem cells and stimulate them to differentiate into the variety of neuron types found in the brain and peripheral nervous system. Repairing and modifying the nervous system will depend on a supply of the appropriate neurons.

We can analyze--either in vivo or in cell culture--the specific factors guiding the growth of connections from one neuron to another. Such knowledge will become vital when we try to build or rebuild neural structures in the brain and peripheral nervous system, leading to desperately needed techniques to restore severed nerves in the limbs and spinal cord. Such needs will drive research and development of new applications.

Finally, we are learning to make long-term connections between neurons and electronic circuits, two very different entities. Neurons can be grown on thin, biologically friendly films that keep the cells separate from the circuits. Each remains in its preferred environment, but they are so close that a circuit can either detect electric pulses in an adjacent neuron, or alternatively, generate an electric pulse strong enough to stimulate the neuron to fire. Simple arrays of electrodes are already used to detect neuromuscular signals generated by the shortened nerves in a severed limb and translate them to useful movements of an artificial limb attached to the stump.

Near-Term Brain Research

Given the pace of molecular biology in unraveling the genome, its controls, and the proteins it generates, we can expect to learn within the next 10 years much of what we need to describe and classify neuron types, to locate them in the embryonic and mature brain, to grow them in cell culture, and connect them with distant neurons, guiding the growth of their axons along pathways marked with biomolecules.

Progress will be slower in creating a "circuit diagram" of the brain--that is, a compendium of the pattern of connections made by the (still unknown) number of neuron groups in the brain. Identification of cell types, embryology, and genetics will speed the process, but it will probably still be somewhat fragmentary 10 years from now.
In the next decade, we still may not completely understand how the neuron "circuits" cooperate to bring about conscious and unconscious mental action, or discover exactly how the mind understands language and music or how it forms and retrieves memories. However, we should learn enough to develop better treatments for mental problems such as bipolar disorder, depression, schizophrenia, obsessive compulsive disorders, and panic attacks. We may understand neurodegenerative diseases, such as Alzheimer's, Huntington's, and Parkinson's, well enough to at least design remedies to slow their progress. Possibly we will find compounds to improve our memory, and others more potent than caffeine yet safer than amphetamines to improve our ability to concentrate.

We should also expect significant progress in the next 10 years toward repairing injuries to the nervous system, especially in the limbs and spinal cord. We will know how to stimulate severed axon and dendrite branches to re-extend themselves toward their original terminations, as well as how to stimulate actual cell division to replace neurons. We will be learning to grow more complicated neural structures with several cell types, looking toward repair and replacement of accessible structures, such as the retina of the eye. Interfacing neurons with electronic circuits will have evolved beyond the "Bionic Man" stage to micro packages that are physically unobtrusive.

Ten years from now, we will be poised to look beyond these simpler applications toward the prospect of direct neural connections to the brain. What will we be looking for? The four key areas of our pursuits will be:
1. Understanding the mind: How does our brain support a mind that lets us see, hear, move, talk, solve problems, fall in love, and develop a sense of identity?
2. Understanding consciousness: What is the physical basis in the brain for the mental sensations of consciousness that accompany such brain activity as seeing, hearing, walking, talking, acting, and the feelings of egotism, fear, pride, love, and beauty?
3. Developing existing human potential: Wherein lie the differences among such diverse individuals as Mozart, Einstein, and the Buddha? Can an individual attain some of their extraordinary powers by focused training and perhaps by stimulated growth of selected neural circuits?
4. Exploring beyond existing limits: Are the mental sensations that we experience all that there can be? Is there a whole world of completely new sensations with associated mental powers that we can explore in some rational way?

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