The Lateralized Brain

The Neuroscience and Evolution of Hemispheric Asymmetries

Sebastian Ocklenburg, Onur Güntürkün, Onur Gunturkun

• Publisher: Academic Press
• Year: 2017
• eBook ISBN: 9780128034538
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

The Lateralized Brain: The Neuroscience and Evolution of Hemispheric Asymmetries is an up-to-date teaching resource for neuroscience faculty members that teach courses concerning hemispheric asymmetries. The book provides students with all relevant information on the subject, while also giving aspiring researchers in the field an up-to-date overview of relevant, previous work. It is ideal for courses on hemispheric asymmetries, that is, the functional or structural differences between the left and the right hemispheres of the brain, and also highlights how the widespread use of modern neuroimaging techniques, such as fMRI and DTI has completely changed the way hemispheric asymmetries are currently investigated.According to the preface, the main aim of The Lateralized Brain is to provide "an up-to-date teaching resource on hemispheric asymmetries … [and] to introduce undergraduate students of all levels to the fascinating topics of hemispheric asymmetries" (p. xv)… (Sebastian Ocklenburg and Onur Güntürkün) have succeeded admirably in their stated aim and are to be congratulated on undertaking the mammoth task they set themselves. They can be proud of what they have accomplished.~ Alan A. Beaton, Department of Psychology, Swansea University, Swansea, UK, in Laterality: Asymmetries of Body, Brain and Cognition, July, 2018.- Includes references to key articles, books, protocols and online resources for additional, detailed study- Presents classic studies that helped define the field- Covers key concepts and methods that are explained in separate call out boxes for quick overview- Provides introductory short stories (e.g. classic clinical cases) as a starting point for each chapter

Chapter 1

Brain Asymmetries—Two Millennia of Speculation, Research and Discoveries

Sebastian Ocklenburg and Onur Güntürkün

Abstract

Scientific inquiries on brain asymmetries in humans started in the early decades of the 19th century. They began with anatomical observations on lateralized cortical folding patterns and then became publicly known by the discovery of language asymmetry by Pierre Paul Broca in 1865. This then was not only a discovery—it was a scientific revolution. In a single step, it introduced two central concepts of neuroscience: first, functions can be cortically localized, and second, left and right hemispheres differ in certain functions. This great success in the discovery of language asymmetry could not be replicated for handedness. Still, the neural foundations of handedness are not fully understood. All attempts to relate it to gross neuroanatomical asymmetries or the crossing pattern of descending corticospinal fibers failed. So, we are still in dire need for a Broca of handedness. The last aspect on the history of brain asymmetries reviewed in this chapter is on facial asymmetries and their possible relation to brain functions. This story starts with the Venus of Milo—a Hellenistic statue that is on display in the Louvre. The story takes twists and turns with many scientists fighting battles against each other until it became firmly embedded in research on asymmetries of language and emotion.

Keywords

Gustave Dax; Pierre Paul Broca; language asymmetry; handedness; face asymmetry; Venus of Milo

Outline

Introductory Short Story 1

Early Reports on Brain Asymmetries 2

The Discovery of Language Asymmetry 4

Are Functions Localized at Cortical Level? 5

Pierre Paul Broca Enters the Scene 6

The Fight for Priority 9

The Many Mysteries of Handedness 10

Is Right-Handedness Caused by an Uneven Blood Supply to the Arms? 13

Are Genes Making the Right Arm Strong? 14

Handedness in the Brain 15

Face Asymmetries 16

Summary 21

Sample Questions 23

References 23

Introductory Short Story

“I have been betrayed. I have been humiliated. They stole my ideas; they neglected my insights and never allowed me to stand on the pedestal of fame that I deserve. I am from the south of France, deep from the province. They never said it publicly, but their eyes gave it away: With my short and pot-bellied stature, my thick southern accent and my lack of this special way of talking that they call ‘distinguished intellect’; I, Gustave Dax, will always be inferior to the academic elite of Paris. My father Marc Dax had discovered that language was governed by the left hemisphere. Yes, I know: Father’s methods of analysis were crude. But, still they were accurate enough to make the point. Father had presented his findings at a congress in Montpellier in 1836. Now the scientists in Paris say that no trace of such a presentation can be found. In 1863 I submitted the collection of findings from my deceased father and more than hundred further cases to the Academy in Paris. A huge data base; absolutely solid and with only a single possible way of interpretation: Language is controlled by the left hemisphere. Thus, the human brain is asymmetrically organized. What a discovery! But what did the Academy do? They sat on my manuscript for 20 months to then reject it in the most dismissive way!

Then came this young fellow; Pierre Paul Broca. Elegant, brilliant, good looking, and with a quality of his scientific work that was vastly superior to anything that I have ever seen. Broca gradually collected more and more cases and finally concluded in 1865 that language was controlled by the third convolution of the frontal lobe on the left side. Language had a cortical location and this location was in the left hemisphere. This is what Broca said. And he simply neglected my manuscript from 1863. He also neglected my paper from 1865 that I had published 2 months before Broca’s final publication. I was simply brushed aside. The Parisian elite can’t stand that a provincial fellow won the race. Broca turned into a scientific celebrity. Wherever he showed up, people kneeled before him as if he was royalty. None of these people ever heard my name. But mine is the priority and I will fight for it until my last day.”

On June 12, 1966 a plaque was unveiled in front of the house in Sommières in which Gustave Dax was born. At the same time the little place in front of this house was renamed as “Le Place des deux Docteurs Dax.” The ceremony to which the President of the World Federation of Neurology had come was to commemorate the discovery by Dr. Marc Dax (1770–1837) and his son, Dr. Gustave Dax (1815–93) on the role of the left hemisphere for language. This discovery had happened about a century before and it was now high time to recognize the contribution of these two physicians. The plaque is small and hangs a bit too high for easy reading. But, on sunny days when people wait for an empty seat in one of the cafes, they may have time to read that it was father and son Dax, who discovered the location of language. And that it happened here, deep in the province.

Early Reports on Brain Asymmetries

The true scientific history of brain asymmetries starts in the second half of the 19th century. This was a time of extraordinary discoveries that completely changed the view on brain functions and set the scene for a modern account of neuroscience that persists today. The epicenter of most of these early breakthroughs on hemispheric asymmetries was France—the leading science nation of its time. But long before this golden era, several scholars foreshadowed what was to follow.

The oldest scientific account on brain asymmetries stems from late antiquity and was written as a medical treatise from an anonymous author who repeatedly refers in his writing to some even older Greek medical texts. His treatise survived about 1000 years possibly by diverse transcriptions, and was finally discovered in a codex that dates from the end of the 11th or the beginning of the 12th century. This codex bears the title De semine (On sperm) and was possibly in possession of the monastery of Saint Pantaleon in Cologne (Germany). In the part on brain asymmetries, the author states: “There are accordingly two brains in the head. The one gives us our intellect, the other provides the faculty of perception. That is to say: the brain on the right side is the one that perceives, whereas the left brain is the one which understands” (translation by Lokhorst¹, p. 302).

How did the author come to this conclusion? According to Lokhorst¹ the ancient view was that the soul was constituted by pneuma—a subtle entity that spreads from the heart to the whole body. Since ancient people often observed that in slaughtered animals and dead people the left cardiac ventricle and the aorta are relatively bloodless after death, it was assumed that the left part of the heart is filled with pneuma and so should be the seat of the soul. Then, it was further assumed that left and right brain hemispheres are connected to left and right heart ventricles, respectively. Since the intellect was seen as superior to the faculty of perception, the first scholarly text on brain asymmetries concluded that the superior faculty of intellect has its place on the left side of the brain, leaving the right hemisphere for the inferior faculty of perception.

A much more empirically driven early account on hemispheric asymmetries was the classic book by Arthur Wigan, The Duality of the Mind.² The discovery that sparked Wigan’s conviction was a chance finding that he had made as a young physician during an autopsy³: The brain of a dead man of about 50 years of age had only one hemisphere. But this person had conversed rationally and even wrote verses just days before his death. Thus, a single hemisphere was sufficient to process all aspects of the mind. Arthur Wigan concluded that if… “one brain be a perfect instrument of thought—if it be capable of all the emotions, sentiments, and faculties, which we call in the aggregate, mind—then it necessarily follows that man must have two minds with two brains: And however intimate and perfect their unison in their natural state, they must occasionally be discrepant when influenced by disease, either direct, sympathetic, or reflex” (Wigan², pp. 201–202). Indeed, it is possible that the loss of one entire hemisphere during very early ontogeny can be (nearly) fully compensated.⁴ However, from this fact it doesn’t follow that the two hemispheres harbor independent minds in the healthy brain. Wigan had published a very radical proposal that was not accepted, and was therefore neglected by the scientific community of his time. More than one century later, however, his thoughts on two parallel minds started to reverberate in a new and fresh way when a young PhD student in Pasadena tested a split-brain patient and discovered that this person indeed seemed to have two minds in one skull. But this is a different story and will be discussed in Chapter 3, The Connected Hemispheres—The Role of the Corpus Callosum for Hemispheric Asymmetries.

In the beginning of the 19th century the main scientific debate was on localization of function. Were the cortical fields doing the same everywhere in a holistic manner or was it possible to locate diverse functions in different areas? This debate also ignited the first discussions about possible asymmetries of cortical functions. Treviranus⁵ was the first to discover that: “Der Mensch hat sehr zahlreiche, sehr tiefe und in beyden Hälften unsymmetrische Windungen. Am großen Gehirn der Affen findet das Gegentheil statt” (Humans have a multitude and deep convolutions that are asymmetrically organized in the two hemispheres. This is different from the forebrain of monkeys).⁵ Similarly, Françoise Magendie, the founder of experimental physiology, surmised a few years later in 1824: “They (the cortical gyri) are differently disposed in every individual; those of the right side are not disposed as those of the left. It would be an interesting approach to endeavor to discover if there exists any relation between the number of circumvolutions and the perfection, or imperfection, of the intellectual faculties—between the modifications of the mind and the individual disposition of the cerebral circumvolutions.”⁶ Magendie’s ruminations run contrary to the basic assumptions of his time: Throughout the first half of the nineteenth century, Francois-Xavier Bichat’s⁷ theory of anatomical and functional symmetry of the cerebral hemispheres prevailed. Bichat’s theory implied that lesions of either side of the brain would have the same effects. But soon, Magendie’s ideas could be grounded on solid data. Together with his friend Louis Pierre Gratiolet, François Leurat, the first true comparative neuroanatomist, published a groundbreaking book in 1839 on the cortical organization of mammals, including humans.⁸ His goal was to understand the evolution of cognition based on the comparative analysis of cortical folding patterns. Leurat observed...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• About the Authors
• Foreword
• Preface
• Acknowledgments
• Chapter 1. Brain Asymmetries—Two Millennia of Speculation, Research and Discoveries
• Chapter 2. Evolution of Asymmetries
• Chapter 3. The Connected Hemispheres—The Role of the Corpus Callosum for Hemispheric Asymmetries
• Chapter 4. Language and the Left Hemisphere
• Chapter 5. Handedness and Other Behavioral Asymmetries
• Chapter 6. Spatial Attention, Neglect, and the Right Hemisphere
• Chapter 7. Recognizing Yourself and Others—The Role of the Right Hemisphere for Face and Self Perception
• Chapter 8. Hemispheric Asymmetries in Emotion Processing
• Chapter 9. Structural Hemispheric Asymmetries
• Chapter 10. Hemispheric Asymmetries Over the Lifespan
• Chapter 11. Sex Differences in Hemispheric Asymmetries
• Chapter 12. Altered Hemispheric Asymmetries in Neurodevelopmental, Psychiatric, and Neurological Disorders
• Glossary
• Index