The Cerebellum E-Book

Dianne M. Broussard

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 439

Veröffentlichungsjahr: 2013

Beschreibung

The Cerebellum provides a concise, accessible overview of modern data on physiology and function of the cerebellum as it relates to learning, plasticity, and neurodegenerative diseases. Encompassing anatomy and physiology, theoretical work, cellular mechanisms, clinical research, and disorders, the book covers learning and plasticity while introducing the anatomy of the cerebellum. Known and proposed "functions of the cerebellum" are addressed on clinical, physiological, cellular, and computational levels, providing academics, researchers, medical students, and graduate students with an invaluable reference.

Leseprobe

Contents

Cover

Title Page

Copyright

Acknowledgments

Introduction

REFERENCES

Section I: The Neuronal Machine

Chapter 1: Structure and Physiology

ANATOMY OF THE CEREBELLAR CORTEX

PHYSIOLOGY OF THE CEREBELLAR CORTEX

SUBDIVISIONS OF THE CEREBELLUM

THE GATEKEEPERS: VESTIBULAR AND DEEP CEREBELLAR NUCLEI

AFFERENT CONNECTIONS OF THE CEREBELLUM

EFFERENT CONNECTIONS OF THE CEREBELLUM

REFERENCES

FURTHER READING

Chapter 2: Operating the Machine

LEARNING IN THE CEREBELLAR CORTEX

PATTERN RECOGNITION BY THE CEREBELLUM

NEURAL NETWORKS

THE CEREBELLUM AS PART OF A “CONTROL SYSTEM”

MULTIPLE SITES FOR CEREBELLAR LEARNING?

THE CEREBELLAR CLOCK

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 3: Plasticity in the Cerebellar Cortex

CEREBELLAR LONG-TERM DEPRESSION

THE CALCIUM TRIGGER

THE SYNAPTIC CONVERSATION

THE MEMORY TRACE

WHAT ABOUT POTENTIATION?

OTHER SITES OF PLASTICITY

INTERNEURONS

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 4: Adjusting the Memory Trace

CONSOLIDATION MECHANISMS

MEMORY TRANSFER AND SYNAPTIC PLASTICITY

MOSSY-FIBER COLLATERALS IN THE DCN

INTRINSIC PLASTICITY IN THE DCN

OTHER CHANGES TO THE MEMORY TRACE

REFERENCES

Section II: Motor Learning

Chapter 5: Learning a New Motor Response

LEARNING IN THE CEREBELLAR CORTEX

CEREBELLAR LTD AND LEARNING

THE ENGRAM FOR THE NMR

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 6: Recalibration for Fine Motor Control

A STABLE PLATFORM FOR VISION

ADJUSTING AN ORIENTING MOVEMENT

ADJUSTING A TRACKING MOVEMENT

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 7: Perfecting Limb Movements by Motor Learning

UPDATING DYNAMIC MODELS

THROWING AND POINTING

SEQUENCE LEARNING

STEPPING AND CHANGES TO GAIT

THE AGILE MOUSE

CONCLUSIONS

REFERENCES

FURTHER READING

Section III: Precision Control

Chapter 8: Coordination

PRECISE OCULAR COORDINATION

COORDINATING THE EYES AND THE HEAD

ERROR CORRECTION FOR LIMB MOVEMENTS

PLANNING FOR MULTIPLE JOINTS

INTERNAL MODELS REVISITED

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 9: Balance and Locomotion

CEREBELLAR ATAXIA

SIGNALS FROM THE INNER EAR

COORDINATING LOCOMOTION

NAVIGATION

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 10: Timing

TIMING USING DISCHARGE RATES

TIMING USING SYNCHRONOUS FIRING

CONCLUSIONS

REFERENCES

FURTHER READING

Section IV: Interpreting the World

THE HUMAN CEREBELLUM

Chapter 11: Intelligence and Language

GENERAL INTELLIGENCE

EXECUTIVE FUNCTION

PROBLEM SOLVING

SPEECH AND LANGUAGE

POSSIBLE MECHANISMS

CONCLUSIONS

REFERENCES

FURTHER READING

Chapter 12: Sensing, Feeling, and Interacting

SENSORY PERCEPTION

ATTENDING TO THE WORLD

PREDICTION

MENTAL IMAGERY

SOCIAL SKILLS

CONCLUSIONS

REFERENCES

FURTHER READING

What Does the Cerebellum Do?

Index

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Library of Congress Cataloging-in-Publication Data

Broussard, Dianne M., author.  The cerebellum : learning movement, language, and social skills / Dianne M. Broussard.   p. ; cm.  Includes bibliographical references and index.

 ISBN 978-1-118-12563-2 (cloth : alk. paper) – ISBN 978-1-118-73007-2 (emobi) – ISBN 978-1-118-73013-3 – ISBN 978-1-118-73025-6 (epdf) – ISBN 978-1-118-73034-8 (epub)  I. Title.  [DNLM: 1. Cerebellum.  2. Executive Function.  3. Neural Pathways–physiology.   4. Psychomotor Performance–physiology.  WL 320]  QP379  612.8'27–dc23

2013027959

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover images: Background art: Margaret Belknap; Top right: Dianne M. Broussard; Bottom left: © istock photo: CEFutcher; Bottom right: © istock photo: PicturePartners Cover design by Modern Alchemy LLC

Acknowledgments

I would like to thank my teachers for having such different views about the same part of the brain. Maurizio Mirolli introduced me to the cerebellum. Hiroharu Noda, Bob McCrea, and Steve Lisberger made it clear that the cerebellum is a worthwhile and fascinating problem. I would also like to thank Helen Bronte-Stewart for her beautifully clear explanation of Marr's hypothesis, long before I found the time to actually read his paper; and Tom Masino, for asking me, “So what does the cerebellum do, anyway?” It took a bit of time, but here is my answer.

All of my colleagues and students have inspired me to write this book; it is really for them, and for their students. I thank Chris de Zeeuw, Jennifer Raymond, Kathy Cullen, Jim Sharpe, Dave Tomlinson, Doug Tweed, Sascha du Lac, Dora Angelaki, Albert Fuchs, Rich Krauzlis, Fred Miles, Jim McElligott, and many others, for asking good questions. I especially thank Jerry Simpson, for being skeptical about the cognitive function of the cerebellum.

My husband and colleague, David R. Hampson, first made me aware of the need for this book by getting me involved in his research on autism spectrum disorders. He has helped in innumerable ways. Thank you especially for the many hours of reading, the feedback, and the many discussions.

Finally, I am tremendously grateful to my daughter, Luci Belknap, for her constant support, encouragement, and sympathy through the long process of writing, and for the cover art.

Introduction

Early modern humans had a problem with brain size. These Stone Age humans probably had very high maternal and infant mortality, even higher than in the so-called primitive societies of modern humans, thanks to their larger crania. The expansion of the cerebral hemispheres had also made it necessary for babies to be born at a more immature stage than modern humans are. What if an increase in the size of the cerebellum, which was relatively small in Cro-Magnon Man, could improve the efficiency of the human brain, allowing the cerebral hemispheres and the diameter of the cranium to become slightly smaller, while maintaining the competitive edge provided by human intelligence? Although we do not know if this in fact did happen, it is consistent with what we do know (Weaver 4). Such an improvement could have allowed more infants, and mothers, to survive childbirth while also allowing infants to be more mature at birth.

The cortex of the cerebellum is a huge, multilayered sheet of neurons that is folded like an accordion. The folds are compressed into a structure resembling a “little brain,” which lies behind and beneath the cerebral hemispheres. But it is not really so little. In humans, if all of its folds were flattened out, the cerebellar cortex would extend for more than 1 m from front to back (Braitenberg & Atwood 1). Several million nerve fibers exit the cerebellum (Glickstein et al. 3). What is the function of all of this processing power and connectivity? What does the cerebellum do? In this book, I will argue that the cerebellum is a supplementary processing device that boosts the computing power of the cerebral cortex—and that it can be used for essentially any task.

It has been said that people born without a cerebellum are nearly normal, but this is a myth. In fact, the few patients with “cerebellar agenesis“ have symptoms resembling severe cerebral palsy. In all known cases, their deficits include severe motor disability and profound mental retardation. What is more, the cerebellum is not completely lacking in any of them; some part of it always remains (Glickstein 2). In fact, the number of cases where the cerebellum has been confirmed to be completely lacking in an individual who survived infancy is zero.

Individuals can survive without most of their cerebellum, but they need a lot of help. Also, we can walk and talk without parts of the cerebellum, just not very well. The cerebral cortex is plastic, and can learn without the cerebellum, and even (to some extent) can compensate for its absence. But having a cerebellum allows us to speed up, perfect, and extend our behavioral repertoire. For animals in the wild (and even occasionally for modern humans), speed is absolutely crucial for survival. Good motor performance can be a matter of life and death.

The first goal of this book is to give a general overview of cerebellar function: what it does, and how it does it. Section I will focus on how the cerebellum works. Section II will show how the cerebellum participates in motor learning. Section III will describe the contribution of the cerebellum to precision, timing, and coordination of movement. Motor control is one of the most complicated things that animals—including humans—do, and the motor functions of the cerebellum allow us to interact promptly and successfully with our environment.

But the cerebellum also has other functions that have nothing to do with motor control. As we will see in Section IV, these include certain aspects of cognition: language, working memory, and attention as well as certain emotional and social functions. More cerebellar functions almost certainly remain to be discovered. There have been difficulties obtaining evidence for nonmotor cerebellar functions, mostly because we are talking about faculties that are exclusively human. The quality of the evidence is improving rapidly, but many clinicians and neuroscientists still believe that “the cerebellum is for motor control.” My second goal is to demonstrate that this view should be changed.

REFERENCES

Braitenberg, V. & Atwood, R.P. (1958) Morphological observations on the cerebellar cortex. J. Comp. Neurol., 109, 1–33.

Glickstein, M. (1994) Cerebellar agenesis. Brain, 117, 1209–1212.

Glickstein, M., Sultan, F. & Voogd, J. (2011) Functional localization in the cerebellum. Cortex, 47, 59–80.

Weaver, S.H. (2005) Reciprocal evolution of the cerebellum and neocortex in fossil humans. Proc. Natl. Acad. Sci. USA, 102, 3576–3580.

Section I

The Neuronal Machine

1 Structure and Physiology

ANATOMY OF THE CEREBELLAR CORTEX

Even the most primitive vertebrates have a cerebellum. For example, the cyclostomes (hagfish and lampreys) have a cerebellum, even though—like other fish—they do not have a cerebral cortex.

The cerebellum may have first appeared as a computational device for the lateral line systems of fish.Lateral lines are rows of tiny hair cells on the skin of fish that detect rocks, fish, and other solid objects. Without their lateral line organs, fish collide with obstacles (Sarnat & Netsky 1974). While swimming alongside a wall, for example, the fish's movement is continually adjusted to maintain a constant distance, based on signals from the lateral lines. Both the lateral line nerves and the central nuclei associated with them send axonal projections into the cerebellum. The purpose of the first cerebellum may have been to carry out computations that allowed fish to use the sensory feedback from their lateral lines to guide swimming.

The cerebellum of cyclostomes works with a very simple structure. It contains only two types of neurons: the tiny and very numerous granule cells, and the large Purkinje cells (P-cells), with their extensive dendritic arbors. The dendrites of each P-cell branch within a flattened, nearly planar field in the molecular layer. Granule cells terminate on and excite the P-cells. P-cells are the only neurons whose axons leave the cortex. Unlike most other large projection neurons of the brain, they inhibit their target neurons.

Both granule cells and P-cells receive afferent input. Granule cells are innervated by the mossy fibers, so called because their axon terminals resemble miniature branches and leaves of moss. In cyclostomes, mossy fibers originate from the lateral line and vestibular nuclei. The P-cells have direct input from the ivy-like climbing fibers, whose cell bodies are located in the inferior olivary nuclei of the brainstem.

Throughout vertebrate evolution, the cerebellar cortex has kept these primitive features and added more. In humans, the cerebellar cortex has three layers (Figure 1.1): the molecular layer, which is a surface layer containing mostly axons; the P-cell layer; and the granular layer. The granular layer contains between 1010 and 1011 granule cells in humans (Braitenberg & Atwood 1958).