Barrel Cortex

Cambridge University Press
9780521852173 - Barrel Cortex - by Kevin Fox and Thomas Woolsey
Frontmatter/Prelims

Barrel Cortex

The barrel cortex contains the somatosensory representation of the whiskers on the face of the rodent and forms an early stage of cortical processing for tactile information. It is an area of great importance for understanding how the cerebral cortex works because the cortical columns that form the basic building blocks of the cerebral cortex can be seen within the barrel cortex. In this advanced graduate- and research-level text, Kevin Fox explores three main aspects of the barrel cortex: development, sensory processing, and plasticity. Initial chapters introduce the topic, describing those animals that have barrels, the functional anatomy of the system, and the cellular and synaptic physiology of the cortical microcircuit. The book concludes with a chapter covering the numerous fields where the barrel cortex is used as a model system for solving problems in other areas of research, including stroke, angiogenesis, and understanding active touch.

KEVIN FOX is currently Professor and Head of Neuroscience, and Head of Research in Biosciences at Cardiff University, as well as Director of the Experimental MRI Centre. He gained his Ph.D. in Neuroscience at the University of London and has worked in the USA at Washington University St. Louis as a McDonnell Fellow, Brown University Rhode Island, and University of Minnesota Medical School Minneapolis as an Assistant Professor.

It is almost 40 years since THOMAS WOOLSEY discoverd the barrel field in studies carried out in his father’s laboratory in Wisconsin. His pioneering work with Henrick Van der Loos, Dan Simons and others has given rise to a large and growing community of scientists who find the barrel cortex an ideal system in which to study numerous questions about the brain. He continues to innovate with the barrel cortex, most recently using in-vivo imaging methods such as hyperspectral interferometry, MRI, and microPET. Tom Woolsey is currently the Director of the James L. O’Leary Division of Experimental Neurology and Neurological Surgery at Washington University St. Louis.

The front cover shows “Cerebral Sublime II,” an image made by Karen Ingham as part of her residency with the Neuroscience Research Group at Cardiff University. The image is based on van Gogh’s “The Starry Night” painted in St. Remy mental asylum near the end of Van Gogh’s life. “Even in the midst of mental turmoil Van Gogh was capable of creating works of sublime beauty, an affirmation perhaps, of the complexity of the mind. We study the brain with a ‘cosmic gaze’ looking at increasingly microscopic cellular images in order to ultimately see ‘the bigger picture’.” (Karen Ingham, Cardiff, 2006.)

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Barrel Cortex

KEVIN FOX
Cardiff University, Cardiff, UK

Foreword by
THOMAS WOOLSEY
Washington University School of Medicine, St. Louis, MO, USA

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CAMBRIDGE UNIVERSITY PRESS
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Cambridge University Press
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Published in the United States of America by Cambridge University Press, New York

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© K. Fox 2008

This publication is in copyright. Subject to statutory exception
and to the provisions of relevant collective licensing agreements,
no reproduction of any part may take place without
the written permission of Cambridge University Press.

First published 2008

Printed in the United Kingdom at the University Press, Cambridge

A catalog record for this publication is available from the British Library

ISBN 978-0-521-85217-3 hardback

Cambridge University Press has no responsibility for the persistence or
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in this publication, and does not guarantee that any content on such
websites is, or will remain, accurate or appropriate.

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This book is dedicated to Richard, William and Anwen

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Contents

	Foreword page  xiii
	Preface  xv
	Acknowledgements  xvii
	Abbreviations  xviii
1	Introduction to the barrel cortex 1
	1.1	Introduction   1
	1.2	System overview  2
		1.2.1	What animals have barrels?  2
		1.2.2	What are barrels?  6
		1.2.3	Why are barrels important?  11
2	Anatomical pathways  14
	2.1	Whisker follicle innervation  14
	2.2	Brainstem nuclei and their projections  17
		2.2.1	General organization of the trigeminal nuclei  17
		2.2.2	Projection patterns of the trigeminal nuclei  19
		2.2.3	Receptive field properties of trigeminal nuclei cells 20
	2.3	Thalamic circuits  23
		2.3.1	General organization of the somatosensory thalamus   23
		2.3.2	The ventroposterior medial thalamic nucleus  24
		2.3.3	The thalamic reticular nucleus  25
		2.3.4	The posterior medial thalamic nucleus  26
	2.4	Barrel cortex  29
		2.4.1	Thalamic inputs to barrels and septal areas  29
		2.4.2	Excitatory intracortical pathways  31
		2.4.3	Inhibitory intracortical pathways  40
		2.4.4	Non-specific innervation  43
	2.5	Cortical outputs  45
		2.5.1	Corticocortical connections  45
		2.5.2	Subcortical somatomotor projections  46
		2.5.3	Subcortical somatosensory projections  48
3	Cellular and synaptic organization of the barrel cortex  49
	3.1	Excitatory cells  49
		3.1.1	Spiny stellate cells  49
		3.1.2	Star pyramids 50
		3.1.3	Pyramidal cells  51
	3.2	Inhibitory cells  55
		3.2.1	Soma-targeting inhibitory cells (basket cells)  55
		3.2.2	Axon-targeting inhibitory cells  56
		3.2.3	Dendrite-targeting inhibitory cells  57
		3.2.4	Other categories of inhibitory interneuron  57
	3.3	Synaptic transmission  59
		3.3.1	Excitatory synaptic transmission  60
		3.3.2	Inhibitory synapses  62
	3.4	Short-term dynamics  64
		3.4.1	Regular spiking, fast spiking and low threshold spiking cells  65
		3.4.2	Short-term dynamics of excitatory connections on to excitatory cells  66
		3.4.3	Factors controlling short-term dynamics  67
		3.4.4	Thalamocortical and layer IV inputs on to inhibitory cells  68
		3.4.5	Layer IV and layers II/III input to layer II/III inhibitory cells  70
		3.4.6	Corticothalamic recurrent collateral to layer IV inhibitory cells  70
	3.5	Electrical synapses  71
	3.6	Organization of synaptic circuits  73
		3.6.1	Single layer cortex  73
		3.6.2	Multilayer cortex  75
4	Development of barrel cortex  79
	4.1	Premaps and clones  80
		4.1.1	Progenitor cells  80
		4.1.2	Columnar and layer development 83
		4.1.3	Tabla rasa concept 85
		4.1.4	Transplant studies  86
	4.2	Pattern formation  87
		4.2.1	Theories of pattern formation  87
		4.2.2	Thalamic afferents  91
		4.2.3	Influence of the periphery  93
		4.2.4	Activity dependence  94
	4.3	Barrel formation  97
		4.3.1	Organization of cellular domains  97
		4.3.2	Interaction of thalamic afferents with neurons  98
		4.3.3	Signaling pathways  99
	4.4	Synaptic development  101
		4.4.1	Thalamocortical synapses  101
		4.4.2	Intracortical synapses  106
		4.4.3	Inhibitory synapses  108
	4.5	Conclusions  109
5	Sensory physiology  111
	5.1	Topography  112
		5.1.1	The columnar hypothesis  112
		5.1.2	Labeled-line processing versus integration  113
	5.2	Intracortical transmission  117
		5.2.1	The thalamocortical response transformation  118
		5.2.2	Vertical transmission within the column  120
		5.2.3	Excitatory transmission between columns  122
		5.2.4	Feedforward and feedback inhibition  124
		5.2.5	Lateral inhibition  127
	5.3	Receptive field organization  129
		5.3.1	Receptive field size  129
		5.3.2	Dynamic receptive field analysis  131
		5.3.3	Cortical and subcortical receptive field components  131
		5.3.4	Velocity sensitivity  134
		5.3.5	Directional organization  135
		5.3.6	Multiwhisker integration  138
	5.4	Dynamic sensory processing  141
		5.4.1	Whisking and active touch  142
		5.4.2	Cortical feedback  145
	5.5	Conclusions  148
6	Synaptic plasticity of barrel cortex  150
	6.1	Long-term potentiation  151
		6.1.1	Historical context and significance  151
		6.1.2	Long-term potentiation at the thalamocortical synapse  154
		6.1.3	Long-term potentiation at the layer IV to layers II/III synapse  157
		6.1.4	Presynaptic long-term potentiation   157
		6.1.5	Mechanisms of long-term potentiation and relationship to experience-dependent plasticity  159
	6.2	Long-term depression  162
		6.2.1	Historical context and significance  162
		6.2.2	Properties and methods of induction  163
		6.2.3	Long-term depression at the thalamocortical synapse  165
		6.2.4	Long-term depression at the layer IV to II/III pathway  166
		6.2.5	Mechanisms of long-term depression and relationship to experience-dependent depression  168
	6.3	Conclusions  169
7	Experience-dependent plasticity  171
	7.1	Map plasticity in barrel cortex  172
		7.1.1	The effect of altered tactile experience  172
		7.1.2	The effect of local cortical interactions on plasticity  177
		7.1.3	Two components to depression of sensory responses  178
		7.1.4	Interactive and non-interactive potentiation of sensory responses  179
		7.1.5	Plasticity at different ages  180
	7.2	The locus of experience-dependent map plasticity  183
		7.2.1	Cortical versus subcortical locus  183
		7.2.2	Pathways for plasticity  188
		7.2.3	Traces of plasticity following deprivation  192
	7.3	Early-phase molecular mechanisms of map plasticity  193
		7.3.1	NMDA receptors  194
		7.3.2	Calcium-calmodulin-dependent kinase type II  195
		7.3.3	Protein kinase A 197
		7.3.4	Kinase substrates: glutamate receptor subunit 1  198
	7.4	Late-phase plasticity: gene expression and structural changes  199
		7.4.1	Structural plasticity  201
		7.4.2	Changes in gene expression  206
	7.5	Injury-induced plasticity  210
		7.5.1	Developmental plasticity  210
		7.5.2	Intracortical plasticity beyond the thalamocortical critical period  212
		7.5.3	Subcortical plasticity in adult animals  213
	7.6	Conclusions  215
8	New and emerging fields in barrel cortex research  217
	8.1	Cortical blood flow and stroke research  218
		8.1.1	Imaging cortical blood flow and oxygenation levels  219
		8.1.2	Dynamic blood flow in the barrel cortex  221
		8.1.3	Metabolic coupling of neuronal activity and blood flow  223
		8.1.4	Models of cortical ischemia  225
		8.1.5	Angiogenesis  226

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