Hemispheric Communication

Mechanisms and Models

Frederick L. Kitterle

• Publisher: Routledge
• Year: 2020
• Print ISBN: 9780805811445
• eBook ISBN: 9781317728658
• Topic: Psychology
• Subtopic: Cognitive Neuroscience & Neuropsychology
• Index: Psychology

The purpose of this book is to provide a comprehensive overview of the way in which the two hemispheres of the brain interact. Some chapters address the nature of this interaction, the anatomical substrates that may account for greater or lesser hemispheric interaction, and the role of sex and handedness in hemispheric interaction. Others address the use of different experimental methods and clinical populations to understand the nature of hemispheric interaction. In addition to current research, this book also provides an important historical overview of the early research questions about hemispheric function and interaction that have helped to shape current views of and approaches to the study of brain function. Special coverage includes:
* a comprehensive history of early research on cerebral laterality and hemispheric communication, including work by Pavlov;
* a critical analysis of techniques and methologies to study hemispheric communication;
* research on anatomical substrates which may underly functional differences between hemispheres and hemispheric communication;
* implications of handedness for hemispheric communication;
* research on individual differences in hemispheric function;
* comprehensive research on sex and handedness from physiological, anatomical, and functional perspectives; and
* attentional differences in hemispheric function.

1 The Corpus Callosum and Hemispheric Communication: An historical survey of theory and research

Lauren Julius Harris

Michigan State University

I am glad to have been invited to contribute to this collection of papers on hemispheric communication: mechanisms and models. I am especially pleased that the editors have thought it appropriate to begin with a consideration of historical issues, themes, and questions. Too often, the historical perspective is treated as a luxury to be dispensed with in favor of more reports of new data.

Which Type Of Hemispheric Communication Should Be Emphasized?

Any historical account of theory and research on hemispheric communication poses several problems and challenges. The first is to decide which type of communication to emphasize: between hemispheres or within? Neuropsychologists know that an understanding of within-hemisphere communication (between, say, the temporal and frontal or parietal and occipital association areas) is critical to understanding higher-order cognitive functions, including memory, attention, language, visuospatial perception, and praxis. Nevertheless, when we say “hemispheric communication,” we invariably think of communication between hemispheres, and that will be the focus here. It is the understandable, if not the only or even necessarily the better, choice for two reasons. First, at an accelerating pace since the 1950s, neuropsychologists have been providing ever more detailed accounts of what each cerebral hemisphere contributes to higher-order functions. Indeed, these accounts have brought theory and research on lateral specialization to the attention of a broader array of scientists, as well as to the general public, than have most other scientific topics over this same period. But, having made so much progress in describing hemispheric differences, we have increasingly come to appreciate that this takes us only part of the way toward understanding the neuropsychological bases of higher cognitive functions, and, indeed, that for certain topics — for example, attention, cognitive development, and individual differences in motor and cognitive skill — the focus on interhemispheric communication may be paramount. Some neuropsychologists and some philosophers also see research on interhemispheric communication as raising thorny philosophical questions about consciousness and personhood, such as “Do two minds exist in one head following split-brain surgery?” “Do the mental properties of the normal brain exist in duplicate, so that disconnecting the cerebral hemispheres creates two separate consciousnesses?” (e.g., Churchland, 1986; Dennett, 1991; Gazzaniga, 1970; Puccetti, 1981; Sperry, 1969, 1983). More and more, then, we are asking how the hemispheres actually communicate. The word communicate, from the Latin communicatus, means “to impart, share,” literally ‘to make common.” How, then, do the hemispheres impart, share, and make common the information they take in about the external world and then process in their respective ways? How do they coordinate their work to achieve normal cognition and action? Neuropsychologists pursuing these questions use a variety of invasive and non-invasive techniques on a variety of subject populations. These include normal persons, individuals with callosal agenesis, neurological patients with callosal lesions (infarcts and tumors), and epileptic patients who have undergone partial or complete callosotomies.

In addition to what we are convinced it will add to our understanding of psychological phenomena, a second reason for emphasizing interhemispheric communication is that the commissures, more than the association fiber tracts, constitute an anatomically clearly defined system on which we can focus our attention and frame questions about mechanism. Understandably, contemporary theory and research regarding interhemispheric communication have concentrated most on the forebrain commissures, the corpus callosum in particular by virtue of its exclusive neocortical origins and its massive size. Less attention has been paid to the other forebrain commissures (anterior and hippocampal commissures) and less still to subcortical commissures such as the posterior commissure, the habenular commissure, or the commissures of the superior and inferior colliculi.

A Long and Winding Road

A more difficult challenge in doing an historical analysis is one common to historical treatments of any scientific topic. It is that, in recounting the ideas, discoveries, and events leading up to our own time, we must take pains not to make the story sound more “progressive” than it really is. Science is progressive, but hardly unremittingly so, and the real story of any scientific enterprise, as every working scientist knows, will recount many more errors, blind alleys, and failures than successes. Often, too, we find some work elevated and other work neglected for reasons related as much to circumstance as to merit. The story of hemispheric communication is no exception.

How to Tell the Story?

The last challenge is logistical: There are a vast number of elements, or strands, in the story, some of them separate, others intertwined, some appearing in the same historical periods, others not. So many time lines makes it hard to tell the story straightforwardly, even if we followed a strict chronology. My strategy is to present the different strands more or less individually, meaning that there will be multiple chronologies, and to point out some of the linking events along the way. The organization is as follows: First, I note the longstanding interest in the question of hemispheric communication and integration; next, I provide a review of the anatomical study of the corpus callosum (here, in particular, we see coincidently developing ideas about function); then, I review experimental and clinical studies of the corpus callosum in animals and humans. This is followed by an account of theories linking mental illness to the supposed breaking down of communication between the hemispheres. I then describe early research on individual differences in the size of the corpus callosum and what these differences were said to reveal about mental functioning; finally, I summarize the “negative” studies of commissurotomy patients in the 1930s and 1940s and the “positive” reports of the decades that followed.

Hemispheric Communication: A Venerable Question in the Science of Mind

I have suggested that the question of hemispheric communication, or integration, looms large today because, having learned much about hemispheric differences, we now better appreciate the need to understand how the hemispheres work together in the service of normal cognition. But questions about communication and integration predate the discovery of lateral specialization. They even predate the two fundamental steps establishing, first, that the brain and not the heart is the source of mind, and second, that the critical brain structure is the soft tissue rather than the fluid-filled ventricles as the physician Galen of Pergamon had taught. If our story has a true starting point, it would be in the recognition that, although our sensory organs come in pairs — two eyes, two ears, two nostrils, two hands — our perceptions of the world are singular. The further recognition that the doubling of sensory organs is repeated in the bipartite structure of the brain itself, and that the processing of the sensory information occurs there, changed the perceptual question into a neuropsychological question.

Among the philosophers and scientists who grappled with this question, two are especially noteworthy. In 1649, in his The Passions of the Soul, René Descartes puzzled over the fact that, although “all the organs of our external senses” are double, so that they register spatially separate images of the same scene or event, “we have only one simple thought about a given object at any one time .” (Descartes, 1649/1988, p. 230). Descartes’ explanation was that the immaterial rational mind was itself unified. By “rational mind,” Descartes meant the soul, a gift of God. Descartes therefore looked for a structure in the brain that could unite these disparate images, a place where the single immaterial mind, or soul, and the double images of the physical body could come together. For Descartes, the best candidate was a “certain very small gland” (“la petite glande”) in the “innermost” part of the brain: the epiphysis cerebri, or pineal gland. Descartes made this choice for several reasons, two in particular. First, in contrast to the double brain itself, the pineal was a unitary, midline structure, the only such structure that Descartes could find in the brain (Descartes, letter to Father Mersenne, April 21, 1641; in Adam & Tannery, 1896-1910, Vol. 3, pp. 119-123; cited in Brazier, 1984, p. 23). Second, the pineal was suspended between the ventricles, or “cells” of the brain, which, following Galen’s doctrine, held the animal spirits (“suspendue entre les cavitez qui contienent ces esprits ...”). The animal spirits, in turn, were thought to transmit messages to and from the nerves, which originated in the walls of the ventricles. The pineal, therefore, appeared to be the only structure that could receive and also unify and control sensory impressions. As Brazier (1984, pp. 2324) has expressed it, Descartes likened the pineal to a control tower. Moving on its base, it directs the flow of spirits to the appropriate pores in the walls of the ventricles, pores that it then opens to allow the spirits to flow out and down the nerves. From the same set of considerations, Descartes (1664/1972) also identified the pineal gland as the seat of imagination and, literally, ‘common sense’.¹ In 1860, the German psychophysicist Gustav Fechner became engaged in fundamentally the same issue. In Elemente der Psychophysik, Fechner observed that despite a “physical multiplicity” of sensory input, the psychological result was unity of consciousness (Vol. 2, p. 526). Unlike Descartes, Fechner also believed that each neural structure (the spinal cord, the basal ganglia, the cerebral hemispheres) might have its own stream of consciousness. Unity of consciousness, therefore, must depend on the spatial continuity of the nervous tissue itself at every level of the neuroaxis. Surmising that, for the cerebral hemispheres, the most relevant nervous tissue was the corpus callosum, Fechner predicted that if the cerebrum were divided by cutting through the corpus callosum, each half brain would have a separate consciousness. Fechner even supposed that if the brains of two men were joined by a bridge of nervous matter, in the same way that the hemispheres of one man are joined by the corpus callosum, the two men would have a single consciousness (and see Footnote 10, further on).

Anatomy

In designating the pineal gland as the means for uniting the disparate images of the external senses, Descartes chose a gray matter structure. Today, we understand (as Fechner...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Contributors
• Preface
• Acknowledgments
• 1. The Corpus Callosum and Hemispheric Communication: An historical survey of theory and research
• 2. Neuroanatomical Bases of Hemispheric Functional Specialization in the Human Brain: Possible Developmental Factors
• 3. Sex Differences in Interhemispheric Relations for Language
• 4. Does The Corpus Callosum Play a Role in the Activation and Suppression of Ambiguous Word Meanings?
• 5. Visualizing the Working Cerebral Hemispheres
• 6. Parameters of the Bilateral Effect
• 7. Independence Versus Integration of Right and Left Hemisphere Processing: Effects of Handedness
• 8. Individual Differences in Characteristic Arousal Asymmetry: Implications for Cognitive Functioning
• 9. Interhemispheric Interaction: Mechanisms of Unified Processing
• 10. Hemispheric Specialization and Cooperation in Processing Complex Visual Patterns
• 11. Spatial-Frequency Selectivity in Hemispheric Transfer
• 12. Coordinating the Different Processing Biases of the Left and Right Cerebral Hemispheres
• Author Index
• Subject Index