notes-books-exploringTheThalamusAndItsRoleInCorticalFunction

1 Introduction

l.A. Thalamic Functions: What Is the Thalamus and What Does It

Do? ==

1.A.1. The Classical View of the Thalamus

1.A.2. Defining Thalamic Nuclei

1.A.3. Major Topics Addressed in This Book

1.B. Thalamic Nuclei and Their Connections: The Classical View 8

1.C. The Thalamus as a Part of the Diencephalon: The Dorsal Thalamus and the Ventral Thalamus 13

1.C.1. The Dorsal Thalamus

1.C2. The Ventral Thalamus

1.D. The Overall Plan of the Next Ten Chapters 22

2 The Nerve Cells of the Thalamus 27

2.A. On Classifying Relay Cells 28

2.A.1. Early Methods of Identifying and Classifying Thalamic Relay Cells

2.A.2. General Problems of Cell Classification

2.A.3. The Possible Functional Significance of Cell Classifications in the Thalamus

2.A.4. Classifications of Relay Cells Based on Dendritic Arbors and Perikaryal Sizes 41

2.A.5. Laminar Segregations of Distinct Classes of Geniculocortical Relay Cells 48

2.A.6. 2.B. 2.C. 2.D. 2.E. 3

The Cortical Distribution of Synaptic Terminals from Relay Cell Axons 52

2.A.7. Perikaryal Size and Calcium-Binding Proteins 61 Intcrncurons 63

2.B.1. Interneuronal Cell Bodies and Dendrites 63

2.B.2. On Distinguishing Interneuronal Axons and Dendrites 66

2.B.3. The Axons of the Intcrncurons 68

2.B.4. Classifications of Interneurons 69

The Cells of the Thalamic Reticular Nucleus 71 Summary 75 Unresolved Questions 76

The Afferent Axons to the Thalamus: Their Structure and Connections 77

3.A. A General View of the Afferents 77

3.B. The Drivers 81

3.B.1. Identifying the Drivers and Their Functions 81

3.B.2. Identifying the Drivers on the Basis of Their Structure 85

3.B.3. The Origin of the Drivers and Their Heterogeneity 90

3.B.4. The Relationship of Two Driver Inputs to a Single Thalamic Nucleus: Docs the Thalamus Have an Intcgrarivc Function? 91

3.C. The Modulators 92

3.C.1. Corticothalamic Axons from Layer 6 Cells 92

3.C.2. Afferents from the Thalamic Reticular Nucleus to First and Higher Order Nuclei 101

3.C.3. Connections from Interneurons to Relay Cells 105

3.C.4. Other GABA-Immunorcactivc Afferents 107

3.C.5. Cholinergic Afferents from the Brainstem 108

3.C.6. Other Afferents to Thalamic Nuclei 110

3.D. The Arrangement of Synaptic Connections in the Thalamus 111

3.D.1. The Four Terminal Types 111

3.D.2. The Glomeruli and Triads 118

3.E. Afferents to the Thalamic Reticular Nucleus 122

3.F. Afferents to Interneurons 125

3.G. Some Problems of Synaptic Connectivity Patterns 126

3.H. Quantitative and More Detailed Relationships 129

3.1. Summary 133

3.J. Unresolved Questions 134

4 Intrinsic Cell Properties 137

4.A. Cable Properties 137

4.A.1. Cable Properties of Relay Cells 140

4.A.2. Cable Properties of Interneurons and Reticular Cells 143

4.A.3. Implications of Cable Properties for the Function of Relay Cells and Interneurons 144

4.B. Membrane Conductances 147

4.B.1. Voltage Independent Membrane Conductances in Relay Cells 148

4.B.2. Voltage Dependent Membrane Conductances in Relay Cells 149

4.B.3. Intcrncurons 173

4.B.4. Cells of the Thalamic Rcticular Nucleus 174

4.C. Summary and Conclusions 177

4.D. Unresolved Questions 178

5 Synaptic Properties 179

5.A. Properties Common to Synapses Throughout the Brain 179

5.A.1. Ionotropic and Metabotropic Receptors 180

5.A.2. Functional Differences Between Ionotropic and Metabotropic Receptors 182

5.A.3. Short-Term Synaptic Plasticity: Paired-Pulse Effects 186

5.B. Synaptic Inputs to Relay Cells 190

5.B.1. Driving Inputs to Relay Cells 190

5.B.2. Inputs to Relay Cells from Interneurons and Cells of the Thalamic Rcticular Nucleus 196

5.B.3. Inputs from Cortical Layer 6 Axons to Relay Cells 200

5.B.4. Brainstem Modulatory Inputs to Relay Cells 202

5.B.5. Other Synaptic Properties 205

5.C. Inputs to Interneurons and Reticular Cells 208

5.C.1. Glutamatergic Inputs 208

5.C.2. Cholinergic Inputs 213

5.C.3. GABAcrgic Inputs 215

5.C.4. Noradrenergic Inputs 216

5.C.5. Scrotonergic Inputs 216

5.C.6. Histaminergic Inputs 217

5.D. Summary 217

5.E. Unresolved Questions 218

6 Function of Burst and Tonic Response Modes in the Thalamocortical Relay 221

6.A. Rhythmic Bursting 221

6.B. Effect of Response Mode on Thalamocortical Transmission 223

6.B.1. Visual Responses of Gesticulate Relay Cells 223

6.B.2. Responses of Relay Cells of Other Thalamic Nuclei 233

6.C. Effect of Response Mode on Transmission from Relay Cells to Cortical Cells 234

6.C.1. Paired-Pulse Effects in Thalamocortical Synapses 234

6.C.2. Relationship of Response Mode to Paired-Pulse Effects 235

6.D. Control of Response Mode 239

6.D.1. Brainstem Control 242

6.D.2. Cortical Control 245

6.E. Summary 247

6.F.Unresolved Questions 250

7 Drivers and Modulators 253

7.A. Drivers and Modulators in the Lateral Geniculate Nucleus 253

7.A.1. Influence on Receptive Field Properties (Criterion 1) 258

7.A.2. Postsynapric Receptors (Criterion 2) 259

7.A.3. Postsynapric Potential Amplitude (Criteria 3-5) 260

7.A.4. Convergence onto Postsynapric Target (Criterion 6) 261

7.A.5. Axon Diameter (Criterion 7) 262

7.A.6. Transmitters (Criterion 8) 262

7.A.7. Paired-Pulse Effects and Probability of Transmitter Release (Criterion 9) 262

7.A.8. Terminal Arbor Morphology (Criterion 10) 263

7.A.9. Innervation of the Thalamic Reticular Nucleus (Criterion 11) 263

7.A.10. Extrathalamic Targets (Criterion 12) 264

7.A.11. Cross-Correlograms Resulting from Input (Criterion 13) 264

7.B. Other Plausible Examples of Drivers Beyond First Order Thalamic Relay Cells 269

7.B.1. Thalamic Reticular Cells 270

7.B.2. Layer 5 Input as a Driver to Higher Order Thalamic Relays 271

7.B.3. Lateral Geniculate Input to Cortex as a Driver 271

7.B.4. Driver/Modulator Distinction for Branching Axons 273

7.C. 7.D. 7.E. 7.F. 7.G. 7.H. 7.I. 7.J.

Tonic and Burst Modes in Thalamic Relay Cells 274

The Sleeping Thalamus 274

7.D.1. Slow-Wave Sleep 275

7.D.2. REM Sleep 277

Can GABAergic Inputs to Thalamus Be Drivers? 277

7.E.1. Extradicnccphalic GABAergic Inputs 277

7.E.2. Interneurons 280

Implications of Driver Concept for Cortical Processing 281

Drivers and Labeled Lines 283

Modulators and Ionotropic Receptors 284

Summary 285

Unresolved Questions 286

8 Two Types of Thalamic Relay: First Order and Higher Order 289 8.A.

Basic Categorization of Relays 289

8.B. Evidence in Favor of Two Distinct Types of Thalamic Relay 294

8.B.1. Structure and Laminar Origin of the Corticothalamic Axons 296

8.B.2. Functional Evidence for Two Distinct Types of Corticothalamic Afferent 298

8.C. Some Differences between First and Higher Order Thalamic Relays 300

8.D. Defining the Functional Nature of Driver Afferent? in First and Higher Order Nuclei 302

8.D.1. Defining the Functional Role of Higher Order Relays 303

8.E. Unresolved Questions 316

9 Maps in the Brain 317

9.A. Introduction 317

9.B. The Nature of Thalamic and Cortical Maps 318

9.C. Early Arguments for Maps 320

9.D. Clinical and Experimental Evidence for Maps in the Geniculocortical Pathway 324

9.D.1. Establishing That There Are Maps 324

9.D.2. The Alignment of Maps with Each Other 326

9.E. Multiple Maps in the Thalamocortical Pathways 330

9.E.1. The Demonstration of Multiple Maps 330

9.E.2. Mirror Reversals of Maps and Pathways 332

9.F. Abnormal Maps in the Visual Pathways 335

9.F.1. 9.F.2. 9.G. 9.H. 9.I. 9.J.

Abnormal Pathways in Albinos 336

Experimental Modifications of the Thalamocortical Pathway 341

Maps in Higher Order Relays 342

9.G.1. Maps in the Pulvinar and Lateral Posterior Nuclei 342

Maps in the Thalamic Rcticular Nucleus 348

General Conclusions 354

Unresolved Questions 355

10 The Thalamus in Relation to Action and Perception 357

10.A. Introduction 357

10.B. Evidence for Branching Driver Afferents to First and Higher Order Thalamic Relays 362

10.B.1. Branching Ascending Driver Afferents to the Thalamus 363

10.B.2. Somatosensory Pathways 364

10.B.3. Mamillothalamic Pathways 367

10.B.4. Visual Pathways 369

10.B.5. Other Afferents to First Order Thalamic Nuclei 372

10.B.6. General Conclusions about Afferents to First Order Thalamic Relays 373

10.C. Branching Corticothalamic Axons from Layer 5 Cells 375

10.D. Implications for Corticocortical Processing 378

10.E. Relating Action to Perception 381

10.F. Unresolved Questions 388

11 Overview 391

11.A. The Drivers 392

11.B. The Modulators 396

11.C. The Thalamic Nuclei 397

11.D. Extending the Functional Analysis from the Thalamus to the Cortex 401

11.E. What Does the Thalamus Do? 402