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ScienceWeek
HISTORY OF BIOLOGY: ON BRAIN AND SOUL
The following points are made by N. Williams (Current Biology 2004 14:454):
1) It is perhaps surprising, given the contemporary eminence of neuroscience within biological research, that it was not appreciated until the 17th century that the brain might have an important function. Conceptual and political upheavals in England at this time served as a backdrop to the major experimental work carried out by a little-known doctor, Thomas Willis (1621-1675) in Oxford, who was key to unravelling the beginnings of our modern view of the brain.
2) Aristotle dominated "natural philosophy" for 2000 years, but he had little interest in the kind of theories you could test. He explained the world by the ends not the means, which did not teach one to look closely at the detail. The Greeks, for example, had a horror of dissecting people. This did not prevent them from offering an account of human biology in which the heart served as the seat of reason, and the brain simply "temper[ed] the heat and seething of the heart".
3) Aristotle's rational soul was both nowhere and everywhere in the human body. Yet Aristotle also believed that specific parts of the body carry out its faculties. He scoffed at the idea that the brain could be such a place, since he saw from his dissections that many animals had no visible brain at all but could still perceive the world and give rise to actions without freezers or formaldehyde to halt its decay, a brain quickly takes on the look and feel of custard -- hardly the stuff of reason and will.
4) The second-century physician Galen (c.130-c.200) mapped the body by dissecting animals and looking at the open wounds of gladiators. When, in 1537, Andreas Vesalius (1514-1564), a lecturer in anatomy at the University of Padua, began to sketch his dissections of human cadavers, he found that people were not made from the animal organs described by Galen.
5) Nonetheless the heart held conceptual sway as a key to the source of thoughts and feelings. But in 1600, the young English doctor William Harvey (1578-1657) studied at Padua. His eventually discovery that the "heart sends blood through the body in a loop" and functioned basically as a pump sent out philosophical shockwaves. Harvey later served as a physician to the English king, Charles I, who introduced him to Viscount Montgomery. Montgomery had fallen from a horse when he was a boy, leaving a gap in his ribs, subsequently covered by a metal plate, which he was able to remove for Harvey. "I immediately saw a vast hole," Harvey wrote, and he was able just to observe the beating heart. I was almost tempted to think that the motion of the heart was only to be comprehended by God." It is understandable, then, that Harvey had trouble persuading his peers of his breakthrough.
6) As civil war loomed, Harvey followed Charles I to Oxford as loyalists and puritans grouped around their centers of support before the battles ahead. Harvey began teaching his theories to some of the students, including a young man named Thomas Willis, who had recently decided to pursue a career in medicine rather than the Church. Harvey now had his disciples, determined not only to trace the course of blood through the body but to follow his experimental methods. Willis eventually tracked the flow of blood to the brain. In attempting to understand its function there, he gave the first account of the network of nerves and blood vessels on which our understanding of that organ is based.
Current Biology http://www.current-biology.com
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COGNITIVE SCIENCE: FROM BRAIN TO MIND
Notes by ScienceWeek:
One of the central problems of modern science is to relate biology to brain, mind, and consciousness. Consider a radio broadcasting the aria Ave Maria sung by Pavarotti. The problem of the cognitive sciences is to understand both the aria and the uniqueness of Pavarotti's voice. The problem of the brain neurobiologist is to understand how vibrations of the speaker produce the various sounds. The problem of the cellular neurobiologist is to understand how the circuits of the radio produce the vibrations of the speaker. The problem of the biophysicist is to understand how the physics of the transistor produces the activity in the circuits. And the evolutionary and genetic and developmental biologists are also involved: How did this particular radio get to be what it is? It seems apparent that none of these specialists can provide the whole story. But why should it be otherwise? The idea that for a highly complex system such as the brain any single level of analysis can provide answers to all riddles is perhaps wishful thinking.
The following points are made by Christian de Duve (citation below):
1) Biologically, we are primates, close relatives of chimpanzees, with which we have more than 98 percent of our DNA in common. In terms of genes, the kinship is even closer, as part of the difference concerns "junk DNA", which has no coding function. Yet, mentally, the distance that separates us from our simian cousins is huge. In the past, this was explained by our having a soul that animals did not possess. Today, the explanation is that we have a bigger brain. What is it about this organ that explains the wonders of mental life? In recent years, this question has become a central topic of research, sometimes referred to as the "last frontier", involving some of the best neurobiologists, psychologists, cognitive scientists, computer experts, and philosophers in the world.
2) Mind is in the head, sustained by the brain. That much we know from everyday experience. What modern science has taught us in addition is that mind and brain are intimately connected, anatomically, functionally, and historically, by linkages that are beginning to be understood. The two are indissolubly linked, leading to the notion that thoughts, feelings, and all other manifestations of the mind are products of the activities of neurons in the brain. The concept is not new. The same was said two centuries ago.
3) "The brain secretes thought as the liver secretes bile." Thus declared the eighteenth-century French physician Pierre Jean Georges Cabanis (1757-1808). The German literature attributes a renal version of the saying to the nineteenth-century Dutch physiologist Jakob Moleschott (1822-1893), who is said to have written: "The brain secretes thought as the kidney secretes urine." In the climate of the times, these affirmations were meant as provocative attacks on the religious belief in an immortal soul. At present, the words have lost their incendiary character and their substance is accepted by most neurobiologists.
4) How could they be faulted? The proofs are there, indisputable, that no manifestation of consciousness is possible without the normal functioning of cerebral neurons. Let this functioning be impaired by lack of oxygen, or by a drug or trauma, and loss of consciousness inevitably follows. Many cases are known in which deterioration of certain specific mental aptitudes, speech, for example, or musical memory, can be related to strictly localized cerebral lesions. Starting in the nineteenth century with the observations of the French physician Pierre Paul Broca (1824-1880) and of the German psychiatrist Karl Wernicke (1848-1905), whose names have been given to the speech centers, a detailed mapping of the brain has been established on the basis of such data.
5) Whereas there can be no consciousness without normal neuronal function, the inverse is far from being true. All the acts of our vegetative life, the coordination of our movements, and many other complex activities are managed by our nerve centers without our being aware of this control or even without our being able to affect it in any way. Many consciously initiated gestures progressively transform, through learning and practice, into unconscious automatisms. We laboriously learn to walk, to ride a bicycle, or to play the piano, finally arriving at a situation in which the control of consciousness has become more a hindrance than a necessity. Even in reasonings, it is often difficult to distinguish the respective parts of the conscious and the unconscious. Whereas the mechanisms of these phenomena remain poorly understood, their structural basis is known.
6) The Latin word "cortex" means bark. As applied to the brain, it designates a thin, specialized structure that covers the entire surface of the organ. The cerebral cortex consists of a sheet of grey matter (rich in cells), about three millimeters thick, characteristically composed of six superimposed cell layers. A dense network of arborescences links the cells of these layers by a very large number of connections, which unfold transversely from one layer to another, and laterally within the same layer. This network is connected to the other parts of the brain and, thereby, to the whole organism by a tight mass of sensory and motor fibers (white matter). The former convey to it sensory impulses coming from all parts of the body, in particular the sense organs. The motor fibers send impulses to all the muscles. These inputs and outputs delineate on the cortex surface a set of specialized areas, which are now well mapped.
7) The cortex is the seat of consciousness; only signals that pass through it give rise to mental experiences. Below the cortex, numerous nerve centers bridge sensory and motor impulses by pathways that bypass the cortex and, for this reason, escape consciousness. The whole of vegetative life is thus regulated in an unconscious fashion. So are many automatic movements, such as those that command the position of the eyes, coordinate gestures, or control balance. Some of these automatisms are inborn. Others are created by learning, descending, so to speak, from the cortex, where they have been set into place, to deeper zones, where cortical surveillance dwindles.
8) It is remarkable that the structure of the cortex is essentially the same throughout the vertebrate series. What changes is its surface area, which reaches 2200 cm^(2) for the human cortex, forcing it to make numerous infoldings, or convolutions, in order to fit within the skull. The surface area of the cortex is about 500 cm^(2) in chimpanzees. In rats, it is four to five cm^(2), which, corrected for body weight, would amount to some 180 cm^(2) for a human-sized rat. It goes on diminishing as we move down the animal scale, but there is the beginning of a cortex as soon as a true brain becomes distinguishable. Even in fish, there is a small cortical area, mainly linked with olfactory centers, which are particularly developed in these animals.
9) These facts suggest strongly that the characteristic, six-layer structure of the cerebral cortex is the generator of conscious experiences and that the richness of these experiences is somehow linked to the surface area of this brain structure. Expansion of the cortical area from 500 to 2200 cm^(2), for example, is what extended the range of problems soluble by the brain, from fishing termites with a twig to sending a man to the moon or engineering life.
Adapted from: Christian de Duve: Life Evolving: Molecules, Mind, and Meaning. Oxford University Press 2002, p.108. More information at: http://www.amazon.com/exec/obidos/ASIN/0195156056/scienceweek
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ON MIND AND BODY AND C.S. SHERRINGTON
Notes by ScienceWeek:
Charles S. Sherrington (1857-1952) loomed over early 20th century neurobiology the way Max Planck loomed over physics. Sherrington was awarded the Nobel Prize for Physiology and Medicine in 1932 for his experimental work in neurophysiology. Sherrington's remarks below on neurogenesis, made 65 years ago, are noteworthy.
The following points are made by Sherrington (citation below):
1) Much as one special organ, the heart, maintains the flow of nutriment throughout the body, so one organ, the brain, is provider of mind for the whole individual. If we smile at so bald a statement, we must yet agree that it states the practical situation with which the physician and the surgeon deal. It shows us too the body in the grip of integration.
2) Much of the body has no demonstrable mind. Of the rest, most has mind only lent to it, in the form of sensation by proxy. Such of it merely communicates with a certain restricted piece of the body, a particular part of a single organ, and there, so much of the body as feels, has its sensation done for it. There too the body's thinking seems to be done for it, namely, in the brain.
3) Of man we know even more confidently than of any other concrete life that his mind is correlated with his brain. But let us avoid the sophistication that for the mind to be in the brain is any self-evident proposition. "Many men," wrote Kant, "fancy they feel their thought in their head, but that is a mistake. No experience tells me that I am shut up some place in my brain."
4) We owe I suppose to medicine in the main the knowledge of where in the body the "seat of the mind", as it is termed, is. But so far from its being a self-evident fact, one of the greatest of biologists, Aristotle, did not subscribe to it although it was accepted by physicians in his time.
5) A brain cell is not unalterably from birth a brain cell. In the embryo-frog, the cells destined to be brain can be replaced by cells from the skin of the back, the back even of another embryo; these after transplantation become in their new host brain-cells and seem to serve the brain's purpose duly. But cells of the skin it is difficult to suppose as having a special germ of mind. Moreover, cells, like those of the brain in microscopic appearance, in chemical character and in provenance, are elsewhere concerned with acts wholly devoid of mind, e.g., the knee jerk, the light-reflex of the pupil.
6) A knee-jerk kick and a mathematical problem employ similar-looking cells. With the spine broken and the spinal cord so torn across as to disconnect the body below from the brain above, although the former retains the unharmed remainder of the spinal cord consisting of masses of nervous cells, and retains a number of its nervous reactions, it reveals no trace of recognizable mind.
Adapted from: C.S. Sherrington: Man on His Nature: Gifford Lectures 1937-1938. Mentor Books 1964.
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