Tai Lieu Chat Luong The Brain: A Very Short Introduction Very Short Introductions are for anyone wanting a stimulating and accessible way in to a new subject. They are written by experts, and have been published in more than 25 languages worldwide. The series began in 1995, and now represents a wide variety of topics in history, philosophy, religion, science, and the humanities. Over the next few years it will grow to a library of around 200 volumes – a Very Short Introduction to everything from ancient Egypt and Indian philosophy to conceptual art and cosmology.
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Smith Leofranc Holford-Strevens SCHIZOPHRENIA TRAGEDY Adrian Poole Chris Frith and Eve Johnstone THE TUDORS John Guy SCHOPENHAUER TWENTIETH-CENTURY Christopher Janaway BRITAIN Kenneth O. Morgan SHAKESPEARE Germaine Greer THE VIKINGS Julian D. Richards SIKHISM Eleanor Nesbitt Wittgenstein A. Grayling SOCIAL AND CULTURAL WORLD MUSIC Philip Bohlman ANTHROPOLOGY THE WORLD TRADE John Monaghan and ORGANIZATION Peter Just Amrita Narlikar Available soon: AFRICAN HISTORY INTERNATIONAL RELATIONS John Parker and Richard Rathbone Paul Wilkinson ANGLICANISM Mark Chapman JAZZ Brian Morton CHAOS Leonard Smith MANDELA Tom Lodge CITIZENSHIP Richard Bellamy PERCEPTION Richard Gregory CONTEMPORARY ART PHILOSOPHY OF LAW Julian Stallabrass Raymond Wacks Derrida Simon Glendinning PHILOSOPHY OF RELIGION ECONOMICS Partha Dasgupta Jack Copeland and Diane Proudfoot GLOBAL CATASTROPHES PHOTOGRAPHY Steve Edwards Bill McGuire PSYCHIATRY Tom Burns EXISTENTIALISM Thomas Flynn RACISM Ali Rattansi THE FIRST WORLD WAR THE RAJ Denis Judd Michael Howard THE RENAISSANCE Jerry Brotton FUNDAMENTALISM ROMAN EMPIRE Malise Ruthven Christopher Kelly HIV/AIDS Alan Whiteside ROMANTICISM Duncan Wu For more information visit our web site www.uk/general/vsi/ Michael O’Shea THE BRAIN A Very Short Introduction 1 3 Great Clarendon Street, Oxford o x 2 6 d p Oxford University Press is a department of the University of Oxford.
It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries Published in the United States by Oxford University Press Inc., New York © Michael O’Shea 2005 The moral rights of the author have been asserted Database right Oxford University Press (maker) First published as a Very Short Introduction 2005 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, or under terms agreed with the appropriate reprographics rights organizations. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this book in any other binding or cover and you must impose this same condition on any acquirer British Library Cataloguing in Publication Data Data available Library of Congress Cataloging in Publication Data Data available ISBN 0–19–285392–9 978–0–19–285392–9 1 3 5 7 9 10 8 6 4 2 Typeset by RefineCatch Ltd, Bungay, Suffolk Printed in Great Britain by TJ International, Padstow, Cornwall To my children Annie and Jack. And to my daughter Linda who died because not enough was known about what to do when stuff goes seriously wrong in the brain.
I hope that some day we shall know enough. This page intentionally left blank Contents Acknowledgements x List of illustrations xi 1 Thinking about the brain 1 2 From humours to cells: components of mind 12 3 Signalling in the brain: getting connected 28 4 From the Big Bang to the big brain 42 5 Sensing, perceiving, and acting 64 6 Memories are made of this 84 7 Broken brain: invention and intervention 102 8 Epilogue 122 Further reading 125 Index 129 Acknowledgements I thank Annalie Clark for her intelligent advice, especially on improving the clarity of the difficult bits. Dr Liz Somerville for her expert tutorial on the fossilized antecedents of the human cranium. Also Jenny for her encouragement.
List of illustrations 1 Anatomical drawing by 6 Hydra, starfish, worm Leonardo da Vinci, and insect 48 c., © Alinari Archives/Corbis Neurobiology, 1997 © Blackwell Science Inc 2 A selection of neurons to illustrate diversity 19 7 Three divisions of the Drawings by Brigette brain early in Zwickel-Noelle, from Reichert, development 50 H., Introduction to Neurobiology From Matthews, G. 13 Neurobiology, 1997 © Thieme New York. © Blackwell Science Inc Reprinted by permission 8 Development of the 3 Neuron-to-neuron forebrain 52 communication 30 From Matthews, G., An Introduction Neurobiology, 1997 to Molecular Neurobiology, 1992 © Blackwell Science Inc © 1992 Sinauer Associates Inc 9 Cephalization 54 4 Action potential and ion From Matthews, G., channels 34 Neurobiology, 1997 From Matthews, G., © Blackwell Science Inc Neurobiology, 1997 © Blackwell Science Inc 10 Homunculus 60 © The Natural History Museum, 5 Paramecium avoidance London behaviour 45 From Eckert, R., 11 Two perceptions from one Animal Physiology, 1978 sensation 65 © 1978 W. Used with permission xi 12 Eye and retina 69 16 Taxi driver 91 From Delcomyn, F., Foundations Reproduced with permission of of Neurobiology, 1997 Punch Ltd © 1998 W.
Used with permission 17 Artificial evolution of robot brain 107 13 Optic pathway – eye to cortex 72 18 Cochlear implant 111 From Neuroscience: The Science of Purvis et al, Neuroscience, the Brain, 2003 3rd edition © Professor Richard Morris/The © 2004 Sinauer Associates Inc British Neuroscience Association 19 Monkey thoughts move 14 Columnar organization in robot arm 114 primary visual cortex 74 Duke University Medical Center Purvis et al, Neuroscience, 3rd edition © 2004 Sinauer Associates Inc 15 Sound localization by List of illustrations coincidence detection 79 From Matthews, G., Neurobiology, 1997 © 2004 Sinauer Associates Inc xii Chapter 1 Thinking about the brain Think for a few moments about a very special machine, your brain – an organ of just 1.2 kg, containing one hundred billion nerve cells, none of which alone has any idea who or what you are. In fact the very idea that a cell can have an idea seems silly. A single cell after all is far too simple an entity. However, conscious awareness of one’s self comes from just that: nerve cells communicating with one another by a hundred trillion interconnections.
When you think about it this is a deeply puzzling fact of life. It may not be entirely unreasonable therefore to suppose that such a machine must be endowed with miraculous properties. But while the world is full of mystery, science has no place for miracles and the 21st century’s most challenging scientific problem is nothing short of explaining how the brain works in purely material terms. Thinking about your brain is itself something of a conundrum because you can only think about your brain with your brain.
You’ll appreciate the curious circularity of this riddle if you consider the consequence of concluding, as you might, that your brain is the most exquisitely complex and extraordinary machine in the known universe. Clearly this is, and may be nothing more than, the opinion of your brain about itself: the brain’s way of thinking about the brain. So it seems we are caught in the logical paradox of a self-referencing, and in this case also a self-obsessed, system. Perhaps the only reliable conclusion from this thought 1 experiment is that the brain is about as conceited as it is possible to be! Notwithstanding the brain’s well-developed personal vanity, we must grant that it provides you with some very distinctive abilities.
It operates in the background of your every action, sensation, and thought. It allows you to reflect vividly on the past, to make informed judgements about the present, and to plan rational courses of action into the future. It endows you with the seemingly effortless ability to form pictures in your mind, to perceive music in noise, to dream, to dance, to fall in love, cry, and laugh. Perhaps most remarkable of all however is the brain’s ability to generate conscious awareness, which convinces you that you are free to choose what you will do next.
We have no idea how consciousness arises from a physical machine and in trying to understand how the brain does that we may well be The Brain up against the most awkward of scientific challenges. That is not to say that the problem cannot in principle be solved, just that the brain is a finite machine and presumably has a finite capacity for understanding. But what are the limits of its intellectual capacity and, at that limit, might we still be asking unanswerable questions about the brain? Neuroscientists accept that they are faced with an awesome challenge. The accelerating pace of discovery in neuroscience however shows that we are a long way from any theoretical upper limit on our capacity for understanding that might exist.