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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
An unprecedented book that discusses a decades long journey of understanding vision and visual impairment through working with patients with brain damage Edward de Haan, a noted clinical vision researcher for the last 35 years, explains how the healthy brain deals with visual information and reveals how he learned to appreciate what it means to be visually impaired. Through discussions of fascinating case studies, he shows that visual deficits are individually unique. Some patients perceive the world without color, some see objects in a distorted manner, whilst others will claim that they can still see although they are demonstrably blind. The author details his experiences with these patients to demonstrate the manner in which patient work is a unique and vital part of discovering how the brain processes visual information. In doing so, Impaired Vision offers a review of the clinical symptoms related to visual impairment and highlights that the patient study method has not lost any of its relevance in our increasingly high-tech world. This important book: * Explores the various clinical phenomena in visual impairment after brain damage * Demonstrates the effectiveness of the patient study method for understanding visual deficits after brain damage * Contains comprehensive coverage of the variety of symptoms that are manifest in patients with visual impairment * Includes compelling case studies of visually impaired patients Written for a general audience but of interest for students, researchers and clinicians, Impaired Vision contains fascinating case studies that offer an understanding of the symptoms that are associated with visuals deficits of brain damage.
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Veröffentlichungsjahr: 2019
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Table of Contents
Cover
Preface
1 Looking at the Brain
1.1 A Short History
1.2 The Brain
1.3 This Book and the Patients in It
2 Blind
2.1 A Blind Eye
2.2 A Blind Brain
2.3 Blind Visual Fields
2.4 Imagined Vision
3 Partially Blind
3.1 Where Is It?
3.2 Line Orientation
3.3 Seeing Stroboscopically
3.4 Shapelessness
3.5 A Black‐and‐White World
3.6 Rough and Matte or Smooth and Glossy
4 Looking but Not Seeing
4.1 Wavelength Without Color
4.2 Day or Night?
4.3 Seeing Without Reading and Strange Connections
4.4 What Is That?
4.5 Lost and an Unfamiliar House
4.6 Face Failures and a Family Affair
4.7 I Can't See Why You Sound Angry and Two Swiss Ladies
4.8 Classic Syndromes of the Parietal Lobe
5 Seeing Things Differently
5.1 Bringing Color to the World
5.2 Moldy Faces and Fish Heads
5.3 Dislodged Vision
5.4 Repetitive Vision
5.5 Lost Feelings
6 Seeing What Is Not There
6.1 Bright Sparks
6.2 Lively Perception in Poor Vision
6.3 Filling in the Empty Spaces
6.4 Neglected but Not Forgotten
6.5 Electrified Perceptions
6.6 Hallucinations Resulting from Degenerative Disease
6.7 Visual Hallucinations in Psychiatric Conditions
6.8 Strange Desires
7 Knowing the Unseen
7.1 Sight Unseen
7.2 Split Brain
7.3 Pointing in the Right Direction
7.4 Vision Without Awareness
7.5 Ignored but Not Forgotten
8 Oblivion
8.1 Seneca's Trouble
8.2 Anosognosia
8.3 Neglect Revisited
8.4 Lost Colors
8.5 My Oil Paintings
8.6 Forgetting Your Amnesia
9 Vision
9.1 Scope of the Visual Brain
9.2 Stages of Vision
9.3 Damage, Deficits, Distortions, and Delusions
9.4 Consciousness
9.5 Looking Back
Index
End User License Agreement
List of Illustrations
Chapter 1
Figure 1.1 Bust of the Greek general Thuycidides.
Figure 1.2 Franz Joseph Gall.
Figure 1.3 Paul Broca.
Figure 1.4 First schema of language functions in the brain, by Carl Wernicke....
Figure 1.5 John Hughlings Jackson.
Figure 1.6 Antonio Egas Moniz.
Figure 1.7 An angiogram of the brain.
Figure 1.8 (a) Median or saggital and (b) horizontal MRI scan of the brain of...
Figure 1.9 Neuron with dentrites, cell body, and an axon.
Figure 1.10 Gray and white matter in the brain.
Figure 1.11 Drawing of the brain by Andreas Vesalius.
Figure 1.12 Some of the main structures of the human brain.
Figure 1.13 Betto Deelman.
Figure 1.14 From left to right: me, Freda Newcombe, and Ziyah Mehta (see Chap...
Chapter 2
Figure 2.1 The human eye.
Figure 2.2 Brigadier and neurosurgeon Hugh Cairns.
Figure 2.3 William Ritchie Russell.
Figure 2.4 Visual pathways running from the retinas, crossing over at the opt...
Figure 2.5 Visual effects after damage to different parts of the optic tracts...
Chapter 3
Figure 3.1 A patchwork of visual areas in the posterior brain.
Figure 3.2 Pointing performance of a patient with bilateral damage.
Figure 3.3 Pointing performance of a patient with left hemisphere (top) and r...
Figure 3.4 Outline of skull defects in all unilateral posterior cases without...
Figure 3.5 The activation pattern of a neuron that is selectively responsive ...
Figure 3.6 Examples of the Efron shapes used for testing shape perception. No...
Figure 3.7 Sensitivity curves for the three cones of the human eye, together ...
Figure 3.8 Spectral sensitivity curves for a normal observer, “AC,” and the p...
Figure 3.9 Examples of different dot‐density textures.
Figure 3.10 Examples of texture stimuli.
Chapter 4
Figure 4.1 The separate colored bands in the rainbow (e.g., violet, blue, gre...
Figure 4.2 Farnsworth–Munsell chips showing (a) free grouping by Morris and (...
Figure 4.3 Examples of stimuli used in a color recognition task involving cho...
Figure 4.4 The Landolt C plate for acuity testing.
Figure 4.5 Example stimuli for a brightness perception test.
Figure 4.6 Example stimuli for the positive‐versus‐negative photograph test....
Figure 4.7 Joseph Jules Dejerine.
Figure 4.8 Hermann Wilbrand.
Figure 4.9 Object agnosic patient of Wilhelm von Stauffenberg.
Figure 4.10 Copy of a line‐drawing of an anchor by the patient Mark.
Figure 4.11 Examples of Gestalt principles, demonstrating (a) the law of prox...
Figure 4.12 Example of overlapping figures.
Figure 4.13 Photograph of the fountain in front of the old Radcliffe Infirmar...
Figure 4.14 Example of a famous face: a photograph of Winston Churchill.
Figure 4.15 Example of a set of intermediate “morphs” showing a face changing...
Figure 4.16 Photograph of a woman making a speech sound.
Figure 4.17 Rezső Bálint.
Figure 4.18 Gordon Holmes.
Figure 4.19 Josef Gerstmann.
Chapter 5
Figure 5.1 Faces and a motor car as put together from separate parts by Ken....
Figure 5.2 Chimeric face stimulus with Patrick Moore (left) and Terry Wogan (...
Figure 5.3 Examples of stimuli used in the odd‐one‐out tests for (a) shape, (...
Figure 5.4 Examples drawn by Marian with distortions on the right‐hand side (...
Figure 5.5 Examples of copies of line drawings made by a patient with visual ...
Figure 5.6 Portrait made by Anton Raederscheidt after he developed left‐sided...
Figure 5.7 (a) Example of a cancelation test with one element. All hearts sho...
Figure 5.8 Example of a patient crossing out the elements of the right‐hand s...
Figure 5.9 Example of the line‐bisection task.
Figure 5.10 The set‐up for the prism adaptation experiment.
Figure 5.11 Copies of a line drawing (original) made by a patient before (pre...
Figure 5.12 Performance of an experimental prism adaptation group (EG) and a ...
Figure 5.13 Artist's impression of palinopsia of an x‐ray of a knee joint on ...
Figure 5.14 Black‐and‐white example of a stimulus display used to demonstrate...
Chapter 6
Figure 6.1 Illustration of jagged migraine phosphenes and their trailing scot...
Figure 6.2 Migraine phosphenes over time, drawn by Otto‐Joachim Grüsser.
Figure 6.3 Wilder Penfield.
Figure 6.4 The homunculus in the motor and somatosensory cortex, as determine...
Figure 6.5 Patient's drawing of his visual hallucination of the lower half of...
Figure 6.6 MRI scan revealing bilateral occipital infarction (radiological or...
Figure 6.7 Left: Linda's recall of Dutch towns from the perspective of the so...
Figure 6.8 Image of a Lewy body in brain tissue.
Figure 6.9 King Nebuchadnezzar, by William Blake (between c. 1795 and 1805)....
Figure 6.10 Detail from the poster for the 1956 film
Invasion of the Body Sna
...
Chapter 7
Figure 7.1 Patient pointing to a visual stimulus.
Figure 7.2 The classic split‐brain phenomenon: a patient responds both with t...
Figure 7.3 Our observations in split‐brain patients.
Figure 7.4 The posting‐in‐the‐letterbox experiment.
Figure 7.5 Posterior brain of the macaque monkey, showing the different visua...
Figure 7.6 The What and How model of Goodale and Milner.
Figure 7.7 Cards used by John Marshall to investigate implicit knowledge in n...
Chapter 8
Figure 8.1 Bust of the Roman stoic Lucius Annaeus Seneca.
Figure 8.2 Photograph of Gabriel Anton.
Figure 8.3 Mooney face of a young female.
Figure 8.4 Photograph of Édouard Claparède.
Chapter 9
Figure 9.1 The different pathways from the eye to the cortex.
Figure 9.2 Percentages of neurons sensitive for four different visual feature...
Figure 9.3 A graphical representation of a deep‐learning network that was tra...
Guide
Cover
Table of Contents
Begin Reading
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Impaired Vision
How the Visual World May Change After Brain Damage
Edward de Haan
University of Amsterdam
This edition first published 2019© 2019 John Wiley & Sons, Inc.
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, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
The right of Edward de Haan to be identified as the author of this work has been asserted in accordance with law.
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Library of Congress Cataloging‐in‐Publication Data
Name: Haan, Edward de, 1957– author.Title: Impaired vision : how the visual world may change after brain damage / Edward de Haan, University of Amsterdam.Description: Hoboken, NJ : Wiley‐Blackwell, [2019] | Includes index. | Identifiers: LCCN 2018051850 (print) | LCCN 2018055295 (ebook) | ISBN 9781119423928 (AdobePDF) | ISBN 9781119423935 (ePub) | ISBN 9781119423911 (hardback)Subjects: LCSH: People with visual disabilities. | Brain damage. | Visual perception. | BISAC: SCIENCE / Life Sciences / Neuroscience.Classification: LCC RE91 (ebook) | LCC RE91 .H36 2019 (print) | DDC 617.7/12–dc23LC record available at https://lccn.loc.gov/2018051850
Cover Design: WileyCover Image: © Wikimedia Commons
For Sarah
Preface
We are truly visual animals. Our hearing, touch, taste, and smell aren't bad, but our best sense is, without doubt, vision. We are only really sure about who has just walked into a room after we have seen them. Vision is our perceptual proof. This is even laid down in law, with formal procedures for a “line up” to identify suspected criminals. Vision provides us with a clear view of the external world, close by and far off. It allows us to recognize the objects, buildings, plants, animals, and people in it. It gives us pleasure when we look at art, the countryside, or dear ones, but it can also instill images of horror that will remain with us for the rest of our lives. That is a lot. Although – on introspection – we do not immediately realize it, we put a lot of effort, or brain power, into seeing. Vision starts with light, which reflects from the external world and is registered by the eyes. The information is relayed via midbrain structures to the back of the brain, where we dedicate some 25% of our thinking power to the processing of visual signals.
How do we do this? How does it work? The nature of visual perception is among the oldest mysteries of mankind. Philosophers in ancient Greece, such as Plato and Aristotle, pondered the complexity and unreliability of this mental skill. Painters and sculptors have worked for centuries to capture and recreate the experience of seeing. And, from the start, scientists have been obsessed with vision and the brain. Perhaps because of this fascination, we now know more about how the brain processes visual information than about any other sense. But we are still grasping at straws when it comes to a full understanding; investigating vision is still work‐in‐progress. There are many ways in which we can study the brain, but there are two basic approaches: we can look at the structure, by scrutinizing the different parts and their interconnections, and we can investigate the functional organization, by trying to infer how the brain carries out the different mental processes and subprocesses. This distinction is not unlike that between hardware and software in computers, although structure and function in the brain are highly intertwined.
Brain damage may affect our vision in many different ways. Some patients perceive the world drained of color, some see objects in a distorted and ugly manner, and some claim that they can see even though they are demonstrably blind. Many such phenomena, such as the inability to recognize faces, have become part of our cultural landscape through the books of Oliver Sacks and the James Bond film, Spectre. As a clinical researcher in the area of vision for the last 35 years, I have seen many patients with impaired vision. In writing this book, my aim has been to produce a work of science for the general public that does justice to the complexity of the subject matter. In addition, such a book might help people to understand the problems of patients with visual impairments. We all have friends or family members who have suffered brain damage as a result of accident, stroke, tumor, or dementia. Physical problems, language, memory deficits; all these possible effects of brain damage are easily recognized, but when vision goes wrong, there is only one person who sees it because visual deficits are private. This book endeavors to be a showcase for the patient study method of investigating vision – a method that dates back as far as the Ancient Greeks but has not lost any of its relevance today. I will describe patients, neurological and psychiatric, who experience visual perception problems as a result of proven or suspected brain dysfunction.
It is only in the interaction between patient and researcher that the best description of the problem can be ascertained. As history proves, these descriptions are often surprising, unsettling, and intriguing. Although the scientific aim is to learn how the healthy brain deals with visual information, the journey itself is of immense personal interest. Imagine what it is like to see the world in different ways.
I have written this book as a personal journey. I will describe how I came across interesting patients, and how I learned from them to appreciate what it means to be visually impaired. During these travels, I was joined for part of the way by many learned colleagues who helped me to understand the different visual problems and the nature of our visual apparatus. Of course, a lot of what I learned came from books and articles. I have always enjoyed reading the original nineteenth‐ and early twentieth‐century papers in German and French, and I have seen the field expand enormously from these early roots. There is another reason for organizing the book as I have. It is just very difficult to remember a long list of clinical syndromes and their features. I hope the subject will come to life when I portray these visual predicaments as short stories of real people encountered in my quest to understanding vision.
A number of the images in this book are printed in grey tones while the essence lies in their color. The reason for this is twofold. First, books are progressively more read as e‐books where you can enjoy these colorful images, and secondly, as a rule we have added the internet URL so anyone who wishes to do so can check the original image on the web.
Finally, I do not use formal references in this book. Most scientific publications today list dozens or sometimes hundreds of books and journal articles that have been used to write them. As this book is, in a sense, a bird’s eye view of my professional life so far, it refers to many more publications than that, probably more like a thousand. I do not feel that it is helpful to fill half this book with one long list of citations. More importantly, this book is intended for the general public as much as for interested students and colleagues. In my view, the majority of readers would – at best – be distracted by the recently cultivated custom to reference every other sentence. What I have done is to try to mention all the colleagues whose studies and/or ideas have had a major influence on my thinking or with whom I have had the pleasure to work. I apologize to those who I forgot, as well as to those who feel left out, but rest assured, I hereby acknowledge their work and I am deeply indebted to all. Despite the lack of citations, however, I am convinced that the avid reader who wants to learn more about a certain topic or from a particular author can easily find more literature on the Web.
1Looking at the Brain
1.1 A Short History
Initially, the structure of the brain was studied in crude ways by dissecting the corpses of animals and humans. Over centuries, more detailed means of investigation were developed, helped by technological advances such as the microscope. The first observations that gave insights into the functional organization came from literary descriptions of people who had suffered brain damage. The following quote comes from the Greek general Thucydides (Figure 1.1), who reported on the effects of the bubonic plague in roughly 400 BC:
Figure 1.1 Bust of the Greek general Thuycidides.
Source: user:shakko. https://commons.wikimedia.org/w/index.php?curid=5573987. Licensed under CC BY‐SA 3.0.
The disease first settled in the head, went on to affect every part of the body in turn, and even when people escaped its worst effects, it still left its traces on them by fastening upon the extremities of the body. It affected the genitals, the fingers, and the toes, and many of those who recovered lost the use of these members; some, too, went blind. There were some also who, when they first began to get better, suffered from a total loss of memory, not knowing who they were themselves and being unable to recognize their friends.
(Thucydides, The History of the Peloponnesian War, Book II, 49, 153)
From this short description, it appears that memory functions may become disrupted after disease. It is also clear that the memory problems may be selective. Some of the survivors were able to talk to Thucydides, so in these patients, speech must have been preserved to a degree. It is conjecture, of course, but it appears that Thucydides was confronted with a large number of patients suffering from a severe brain disease, and he observed that language and memory are separate mental abilities. He had stumbled on an important principle: some functions may become disrupted selectively while others remain intact. He could not guess where the responsible damage in the body – or in the brain, for that matter – was located. He had no means to assess the internal physical locus of the problem.
The opposite was true for the early anatomists, like Galen (second century) and Vesalius (sixteenth century), who were able to look inside the head (post mortem) and who created more and more precise drawings of the brain. Despite their detailed observations, they were somewhat at a loss about functional organization. They could see where the nerve fibers from the sensory systems (e.g., eyes and ears) reached the brain, and inferred correctly that those parts were involved in perception. They were also correct in concluding that motor planning took place in the areas where the nerve fibers that innervate the muscles originate. Apart from these “input” and “output” systems, however, it was extremely difficult for them to determine what the different parts of the brain were doing. For a long time, it was almost impossible to study brain structure and brain function simultaneously. In order to understand how the brain really works, these two approaches needed to be brought together.
One of the first to try to do this was the much vilified Franz Joseph Gall (Figure 1.2). He started his quest for function localization, which he called phrenology, in the late eighteenth century, without a means of looking inside the head. Instead, he suggested that we could use the shape of the head to infer the degree to which a person possessed a certain mental ability. His reasoning was as follows. First, he postulated that all our mental abilities are carried out in the brain (and not, for instance, also in the heart, as many argued at the time). Second, he suggested that specific abilities, such as memory and speech, are carried out in dedicated parts of the brain, which he called “organs.” In addition, he suggested that the size of each organ depends directly on the degree to which a person possesses its associated ability. Thus, by using the analogy of the muscle – more muscle mass means more power – he argued that someone with the “gift of the gab” will have a large language organ in his or her brain. As this particular organ is positioned at the front of the brain, he further suggested that such a person will have protruding eyes. This last suggestion, that the shape of the head gives away detailed information regarding mental abilities and personality traits, such as trustworthiness or patriotic tendencies, was actually not proposed by Gall at all. It is called physiognomics and was popularized by Johann Kaspar Lavater in the second half of the eighteenth century, although its origins can be traced back to Aristotle. Physiognomics has not stood the test of time, not in the least because of the more and more outrageous claims made by its practitioners. For instance, a low forehead, high cheekbones, and a flat nose were all supposed to be signs of aggression, although it was clear that these features often occur in people who are, not aggressive at all. In addition, the descriptions became more and more frivolous, such as facial signs for agility and cynicism.
Figure 1.2 Franz Joseph Gall.
Source:https://commons.wikimedia.org/wiki/File:Franz_Josef_Gall3.jpg.
Gall's phrenology was rejected ultimately not because of his use of physiognomics but by early physiological experiments. Gall's proposals were reviewed for the Académie Française by a committee chaired by the pioneer physiologist, Marie Jean Pierre Flourens (1794–1867). Flourens had carried out experiments in which he made surgical lesions in the brains of living rabbits and pigeons, and carefully observed the effects on their behavior. He concluded that, irrespective of the location of the lesion, all functions were affected to an equal degree and that the size of the lesion determined the severity of the impairments. His observations led to the doctrine of “Action Propre”: the position that the brain functions as a whole and that there is no differentiation of function. Gall's scientific career was finished.
It was not until the second half of the nineteenth century that the combined structural and functional investigation of the human brain commenced in earnest. Neurology developed rapidly as a new discipline within the medical arena in many academic centers in Europe, most notably Paris. Paul Broca (1794–1867, Figure 1.3) was a leading researcher who advocated the careful observation of brain‐damaged patients, followed by detailed post‐mortem examination of their brains. This research method demands great diligence, determination, and creativity. Psychology was in its infancy, and the description of mental abilities was still uninformed. Therefore, these clinicians had to discover new ways of describing the impaired behavior of their patients. Subsequently, they had to wait sometimes years until the patient died in order to carry out an autopsy. Finally, they had to find a conceptual framework for relating impaired functions to the damage they observed in the brain. They were neurologists, psychologists, and anatomists in one, initially without a clear theory of how the brain works.
Figure 1.3 Paul Broca.
Source:https://commons.wikimedia.org/wiki/File:Paul_Broca.jpg.
These scientists learned fast. Broca described a patient, Tan, who was unable to speak as a result of damage to the front of the left part of his brain, or left hemisphere. Later, Carl Wernicke (1848–1905) reported on a patient with damage to the middle of the left hemisphere who was poor at understanding spoken language. Wernicke compared his patient with Broca's, and subsequently did two important things. First, he concluded that these two patients, with different language problems and different lesions, showed that in healthy people language perception and language production are separate processes located in different parts of the brain. Second, he made a prediction. He argued that these two language areas in the brain must be connected, and that if the connection were to be selectively cut by focal brain damage, the patient would show no language perception or speech problems but would be unable to repeat accurately what was said to him or her (see Figure 1.4). That was a bold prediction, but, lo and behold, in 1885, Ludwig Lichtheim (1845–1928) reported exactly such a patient. This was the beginning of a long tradition – a tradition that was to build the first theories of function localization, and a tradition that has lost none its relevance.
Figure 1.4 First schema of language functions in the brain, by Carl Wernicke.
Source: M. Catani & M. Mesulamb (2008). The arcuate fasciculus and the disconnection theme in language and aphasia: History and current state. Cortex, 44(8), 953–961. Reproduced with permission of Elsevier.
But now back to vision. The early nineteenth‐century explorations of brain function revealed a number of patients with surprising visual impairments. For instance, the English neurologist, John Hughlings Jackson (1835–1911, Figure 1.5), was the first to describe a patient with what he called “imperception.” Following damage to the posterior part of both sides of the brain, this patient was unable to recognize objects, faces, or text, although she was obviously still able to see: she could point to targets and could easily move around in a furnished room without collisions. Hughlings Jackson suggested that, although the visual signals from her eyes did reach her brain and she could still see in a way, the patient was no longer able to recognize the world around her. Everything was new to her. This was the first in a long series of patients with visual problems, stretching into the present. These patients, and the scientists who investigated their visual impairments, beginning with Hughlings Jackson, have provided us with the basic understanding of our visual brain.
Figure 1.5 John Hughlings Jackson.
Source: Wellcome Collection. https://wellcomecollection.org/works/qv6rwm3p?query=L0000492&wellcomeImagesUrl=GET%20/indexplus/image/L0000492.html%20HTTP/1.1. Licensed under CC BY 4.0.
In 1878, Hughlings Jackson started the prestigious scientific journal Brain, which has published many patient reports over the last 150 years. In my view, he was one of the most important pioneers of the brain sciences. Not only was he an insightful clinician publishing detailed reports on neurological patients and a succinct science communicator, but he also had the ability to step back and think about the great central questions, such as: Where does conscious awareness come from? Based on his work with epileptic patients, he suggested that perceptual information is first processed at a subconscious level at the back of the brain, where, via a process of survival of the fittest, the best description of what is seen is selected. This information is then passed on to the language areas on the left side of the brain, where it becomes conscious. These ideas were all published well before Sigmund Freud developed his ideas about consciousness. As Freud was trained in the tradition of the early neurologists, it is very likely that he knew of Hughlings Jackson's proposals about conscious and unconscious processing. However, he never referred to Hughlings Jackson.
An important breakthrough in the investigation of the structure of the brain was the emergence of medical imaging, starting with the discovery of x‐rays by Wilhelm Röntgen (1845–1923) in 1895. This high‐frequency electromagnetic radiation can be used for the imaging of body parts, as it penetrates the body relatively easy and is absorbed much more by bone than by soft tissue such as muscles and skin; that is why bone is darker than the surrounding tissue on an old‐fashioned x‐ray. At first, this method produced very coarse images of the head, which showed the brain with little detail, but neurologists soon began to develop some clever ways of improving it. For instance, the Portuguese neurologist Antonio Egas Moniz (1874–1955, Figure 1.6) had the brilliant idea of injecting contrast fluid, which has the capacity to block x‐rays, into the large arteries supplying blood to the brain. This fluid distributes naturally through the vascular network, giving an x‐ray image (or angiogram) that shows the brain vasculature in detail (see Figure 1.7). Angiograms are helpful in detecting bleeding, areas that have died (no working blood vessels), and malformations in the blood circulation within the brain. This was obviously a great step forwards in neuroimaging.
Figure 1.6 Antonio Egas Moniz.
Source:https://commons.wikimedia.org/wiki/File:Moniz.jpg.
Figure 1.7 An angiogram of the brain.
Source: Glitzy queen00. https://commons.wikimedia.org/wiki/File:Cerebral_Angiogram_Lateral.jpg.
Egas Moniz received the Nobel Prize in 1949 – not for the discovery of the angiogram, but for the development of the lobotomy. The lobotomy is a surgical procedure in which the frontal parts of the brain are lesioned in order to alleviate the symptoms of mental disorders. After a short period of popularity in the 1940s and '50s, this treatment was rapidly abandoned when it became clear that the beneficial effects were limited and the side‐effects disastrous. The film One Flew Over the Cuckoo's Nest ends, sadly, with the main character, played by Jack Nicholson, being treated with a lobotomy to cure his unruly behavior. There is a small museum in the Santa Maria Hospital in Lisbon where one can see the surgical implements that Egas Moniz constructed to perform the operation.
The first Röntgen machines used photographic plates or films to visualize images of the brain, but with the development of computers, these plates were replaced by detectors. With new image analysis software, more detailed computed tomography scans, known as CT or CAT scans, were able to differentiate bodily structures. It also became possible to visualize the structure of the brain and more types of brain damage. These developments had a great impact on the study of the brain. Scientists no longer needed to wait until the patient died to determine the location of the brain damage, and as a result, brain research changed up a gear.
A major conceptual breakthrough in brain research took place in the 1960s when David Hubel (1926–2013) and Torsten Wiesel (1924) pioneered the use of micro‐electrodes to probe the functional characteristics of individual cells in the visual system. An extremely thin electrode was positioned in the gray matter of the brain of a cat or primate in an area that was known to be involved in vision. In contrast to white matter, which comprises bundles of axons connecting brain cells, the gray matter consists of the cell bodies. Brain cells or neurons are not silent, and even at rest they produce a steady but low‐frequency train of depolarizations or “spikes.” These “spikes” consist of an electrical discharge that travels along the axons. In this way, neurons communicate with one another over distance. As spikes are electrical in nature, they can be registered with an electrode. It is even possible – if you connect the electrode to an amplifier and a loudspeaker – to make the spikes audible as short bursts of noise. When a neuron becomes activated, the frequency of spikes increases significantly. Through the loudspeaker, this sounds like a sudden, fast train of bursts of noise. During a typical experiment, the animal is shown a large number of different visual stimuli, such as patches of different color, dots moving in different directions, or line segments of different orientations. Using statistical analyses, the type of visual input is subsequently correlated with the activation level of different neurons. Thus, when neurophysiologists have discovered a neuron that responds strongly to the color red, they have shown that the increase in firing rate is significantly higher in response to red patches compared to all other visual stimuli. The conclusion is that this neuron is involved in the processing of red. This is true not only for basic visual features, such as color and orientation, but also for more complex visual cues. David Hubel, who won the Nobel Prize for his studies probing the brain with micro‐electrodes, explains this further:
The brain is a tissue. It is a complicated, intricately woven tissue, like nothing else we know of in the universe, but it is composed of cells, as any tissue is. They are, to be sure, highly specialized cells, but they function according to the laws that govern any other cells. Their electrical and chemical signals can be detected, recorded and interpreted and their chemicals can be identified; the connections that constitute the brain's woven feltwork can be mapped. In short, the brain can be studied, just as the kidney can.
In the early 1980s, David Perrett was studying the visual brain of macaque monkeys using micro‐electrodes. To his surprise, he found single cells that responded selectively to the face of a particular person known to the monkey (and not to other people who were familiar to the monkey or any other visual stimulus). Just as Hubel and Wiesel had found neurons that respond selectively to certain line orientations, so David Perrett had discovered brain cells that are sensitive to a particular familiar face. Surely the location in the brain of these “red” and “face” cells must be indicative for the brain structures responsible for the perception of red and the recognition of faces? Over the course of decades, using these methods, scientists have drawn up a map of the visual brain, consisting of many areas that were more or less selectively “tuned” for certain features, such as orientation, motion, and color, but also objects and faces.
The electrical activity in the brain can also be registered from outside the head with electrodes that are fixed to the head with glue, in what is known as an electroencephalogram (EEG). The electrical energy produced by one neuron is, of course, very weak, so it is only possible to pick up a signal from large numbers of brain cells firing in unison. EEGs are used as clinical tools, for instance in the diagnosis of epilepsy. In order to study healthy functions of the brain, a method called “evoked responses” has been developed. If one measures the electrical brain activity in response to a particular stimulus (e.g., a subject presented with a red patch in his or her visual field), it is impossible to distinguish it from the background noise caused by other external stimulation and internal processing. The solution is to repeat the same stimulation a large number of times and to make an average of all the recordings. Assuming that the background noise is uncorrelated to the stimulation, averaging is expected to reduce the noise, as random noise signals will cancel one another out. Scientists consider that this will increase the signal/noise ratio dramatically, and the result will be a good representation of the brain activity involved in seeing “red.” The advantage of this research method is that it provides information regarding functional organization with great precision in time. Unfortunately, it is less precise in pinpointing the locations of activity in the brain.
The search for a method to study brain function in healthy subjects continued in full force in the 1980 and '90s. Clinicians were looking for an alternative to x‐rays, because too much exposure to x‐ray radiation is known to increase the risk of diseases, such as cancer. The alternative, magnetic resonance imaging(MRI), was developed by, among others, the Nobel Prize winners Peter Mansfield and Paul Lauterbar. The physics driving this imaging tool are complex, but what it boils down to is that MRI can measure the amount of an atom, such as hydrogen (the H in H2O), in precisely localized units in the brain. The powerful research machines that we have today can measure units as small as 0.1 × 0.1 × 0.5 mm. (These three‐dimensional units are called voxels, as compared to the two‐dimensional pixels on your computer screen.) Given that different structures (e.g. gray matter, white matter, blood, liquor, and bone, as well as malignant structures such as tumors) contain different amounts of hydrogen, it is possible to produce extremely detailed structural images of the brain. Figure 1.8 shows an MRI image of the brain of a patient, Mark, who will be presented in detail in Chapters 3 and 4. As one can see, these images are extremely precise.
Figure 1.8 (a) Median or saggital and (b) horizontal MRI scan of the brain of a patient with large, bilateral ventro‐medial lesions.
Further technical developments allowed for the measurement of the density of other atoms than hydrogen, such as oxygen, and this led the way to using MRI for functional neuroimaging (functional magnetic resonance imaging or fMRI). Neurons are hungry cells that require food and oxygen for their energy supply. When a certain part of the brain is active at a certain point in time, oxygen is transported to it by the brain arteries. Large differences between oxygenated and deoxygenated blood thus indicate where the brain is at work. The colorful pictures you will have seen of the brain functioning are, in fact, structural MRI images with areas of activation superimposed. As fMRI pioneer Peter A. Bandettini explains:
With the fMRI results in the very early nineties, MRI itself took on an entirely new direction. Rather than MRI providing only anatomic and some basic physiologic information, it now could produce dynamic brain activation maps quickly, non‐invasively, and with relatively high resolution. Many MRI technicians, industry engineers, marketing people, radiologists, scientists and others of the MRI establishment were nonplussed as researchers started having healthy volunteers, in the name of brain activation, doing all kinds of odd things in the magnet other than simply lying perfectly still with eyes closed – then producing highly processed and wildly colored maps rather than the standard grey scale. A revolution had begun. We could now look into the human brain as never before – and we were leveraging mostly established technology to do it.
The study of the functional organization of the brain has changed dramatically over the last two decades. Experiments with animals have become increasingly controversial and, partly in response to the societal demands for good animal care, extremely expensive. The number of animal studies has thus gone down substantially, and this trend is expected to continue, especially for invasive methods. The careful evaluation of brain‐damaged patients as a way of investigating the functional organization of the brain, namely patient studies, has also become less common, because it requires expert clinicians who must see many patients to recognize interesting but often rare phenomena. As a rule, patients find it very difficult to put their problems into words, so a research clinician will need to know exactly what to ask and how to recognize the signs that indicate an interesting visual problem. In addition, clinical research demands a good command of the clinical assessment of cognitive and emotional problems, as many cognitive impairments, such as attention and memory problems, may interfere with seeing. What might look like a visual problem may in fact be caused by a memory problem. Excluding alternative explanations is a hallmark of good clinical research. Finally, the medical ethical rules and regulations have changed enormously over the last few decades. In my view, they used to form a sensible system for the protection of the interests of patients based on the careful weighing of the possible benefits of new insights against the potential risks posed by a clinical study. That system has now evolved into a very complex, convoluted affair set up to avoid legal claims against hospitals and, in particular, pharmaceutical companies. Based on the one‐size‐fits‐all principle, researchers such as myself who restrict themselves to visual experiments and imaging have to comply with the same prohibitive procedures as those who are involved in the riskiest development of new drugs.
With animal and patient studies on the decline, most research since the year 2000 has used fMRI and EEG to investigate brain function. Functional neuroimaging in healthy subjects has now become the dominant method. Is that bad? No, it is not bad, but it also not good. There are two reasons why we should cherish patient studies in addition to functional imaging.
First, both patient studies and functional imaging studies have their own shortcomings. The object of patient studies is the damaged brain, and this by definition is not comparable to a healthy one. To assume a simple subtraction logic – a damaged brain is a normal brain minus a specific (damaged) function – is frivolous to say the least. On the other hand, functional imaging tools like fMRI and EEG are indirect measures of brain activity. Localization of function is more inferred than measured. Thus, it is wise to use more than one method to make a particular point; two noisy or unreliable information channels together may provide a clear and reliable signal. This is an important reason why we should continue to practice patient studies in addition to imaging. It also appears that functional imaging is better for hypothesis testing, while patient studies are better for developing hypotheses. When the subject lies in the scanner, he or she has to perform a specific task, like looking at pictures of faces or pointing at visual targets. Whatever the task is, it has always been designed by the experimenter to answer a certain question. For example, which parts of the brain are involved in face perception or spatial localization? This dependency on predetermined experimental manipulations means that there is little room for serendipity. In contrast, surprising new findings are at the heart of studying neurological patients. An unexpected complaint or a surprising error on a task may provide a new clue about how the brain works. Looking at it in this fashion, one could argue that patient studies may be very productive in generating new hypotheses, while functional neuroimaging with very well‐controlled experimental conditions may be better placed for testing these hypotheses in healthy people.
Second, there is the difference between causal and correlational inferences. Functional imaging is more often than not correlational, while patient studies provide evidence for cause‐and‐effect relationships. Functional imaging can show that two things coincide or happen together in time. To make this point clearer, let us consider an fMRI experiment where the perception of one’s own hand is being investigated. Subjects are scanned while they are presented with a large number of different photographs of hands – both other people's and their own. The results show that relative to perceiving other people's hands, there are two areas in the brain that are more active while perceiving one's own. What have we learned? Is it that both these areas are involved in the perception and recognition of one's own hands? Not necessarily. We only know that these areas are activated when one's own hands are seen. Thus, it might also be the case that one or both of these areas is involved in moving one's hands. In fact, it could be any association that one's brain makes with one's own hands. It might even be an area that is involved in visual pleasure, if one enjoys looking at one's own hands more than at other people's. In contrast, if a particular part of the brain is damaged in a patient, and as a result he or she can no longer recognize his or her own hand, then it is clearly the case that either that brain structure is directly involved in hand perception or that it is part of a pathway of a network involved in hand perception. Thus, while the decline in animal studies is foremost an ethical issue, the focus on neuroimaging in studying the human brain is perhaps best described as a missed opportunity. Many patients with brain damage or disease would be happy to share their predicament with clinicians. This book focuses on clinical research with these patients.
Now, before we get to the meat of the book, there are two questions that need to be addressed. What is a function, and what is localization? Two straightforward questions, and clearly relevant to the issues at hand. They are, however, not so easy to answer. In fact, they are so hard that some researchers have decided to leave them to one side and get on with their other business. Not a very good start for a scientist who wants to localize functions.
In attempting to answer these questions, it is useful to be aware of a number of pitfalls. First, the idea about what constitutes a function comes directly from common sense. In everyday life, we use words like “memory,” “attention,” and “vision,” and we have a common understanding that these terms refer to specific mental abilities. There is good reason to believe that there is some truth in this approach, as clinical studies have shown that some patients may suffer from, say, a memory problem while maintaining most of their other mental abilities intact. Things become a bit fuzzier when we start looking at subdivisions. Let's take a closer look at memory. It is possible to check whether someone has remembered an event by asking him or her to recall what, for example, “happened yesterday at 5 o'clock at the train station” or by offering a multiple‐choice format in which he or she has to choose what happened from four possible events. This is the difference between recall and recognition: clearly two different memory tasks, but the question is whether they measure the same or two different memory functions. The borders between functions appear even less well defined when we zoom in on a more specific memory task, such as visual recognition (e.g., recognizing a tree in a picture of a park). Is this memory, or is it perception? Obviously, all our mental abilities interact, and it is not immediately clear what aspects of them are separate entities. But this is what we need to know if we want to localize functions in the brain. Imagine that we are trying to localize a function that is actually represented in the form of two or three separable subprocesses. We might observe many different patients who show a deficit in that function. In fact, we might well conclude that it is not the location but the size of the lesion that is important for developing this impairment. In short, for localization, we need a good idea of all the subprocesses that constitute a mental function. Our current ideas or models of mental functioning are still approximations, and we should remain aware that it might not be possible to distinguish the localizable subprocesses of a certain function.
The next problem we encounter when we want to localize functions concerns individual differences. In the nineteenth century, Paul Broca postulated that the left frontal brain was the seat of language production. At that time, most of his colleagues assumed that this must be the case for everybody. We now know that the brain structure called the posterior inferior frontal gyrus, also known as Broca's area, varies widely in size and shape between individuals and cannot be identified reliably in a substantial number of normal healthy people. We also know that in about 10% of normal healthy people, language is represented not in the left but in the right hemisphere. These variations mean that localizing mental functions is not absolute but probabilistic. There are substantial differences between individuals in terms of both brain structure and brain function. A metaphor would be the comparison between an expensive sportscar and a family car. They serve the same purpose but are put together very differently. In addition, the steering wheel will be on a different side depending on what country the car was built in: sometimes on the right and sometimes on the left.
In publications on how the brain works, we often see images of the brain (e.g., an image produced by an MRI scan) with superimposed colored blobs, indicating where a specific function is localized. It is important to realize that these blobs are drawn on top of the brain image by the investigator and have not been generated automatically. They are just a way of summarizing the results and presenting the researcher's conclusions. This method of communicating function localization suggests that a given bit of the brain is exclusively dedicated to a particular process. In fact, we know very little about how functions are organized at the level of neurons. It is very likely that networks of neurons are the basic structure and that these networks may involve both close and distant connections. It also likely that there are many overlapping networks. This means that a particular part of the brain could be involved in many different processes. There is clearly little ground for thinking that localization is in any way exclusive for a particular function.
So, all in all, it is a tricky business. Brain functions may be localized in a distributed fashion in different locations in different individuals, whose brains may have different shapes. Then again, nobody said it was going to be easy to understand the brain. To get an idea of its complexity, it is instructive to look at the different problems patients may encounter – which is the subject of this book.
