EEG - fMRI (eBook)

Foreword 5
Preface 7
Contents 10
Contributors 20
Part I Background 23
1 Principles of Multimodal Functional Imaging and Data Integration 24
1 Introduction 24
2 Modes of Data Integration 25
3 Multimodal Data Acquisition Strategies: Degree of Synchrony 28
4 Multimodal Data Integration Strategies 29
4.1 Spatial Coregistration 29
4.2 Asymmetric Integration 30
4.3 Symmetrical Data Fusion 31
5 Summary 33
References 34
2 EEG: Origin and Measurement 39
1 Introduction to the Electrophysiology of the Brain 39
2 Origin of EEG and MEG I: Cellular Sources 40
3 Main Types of Rhythmical EEG/MEG Activities: Phenomenology and Functional Significance 42
3.1 Sleep EEG Phenomena 42
3.2 Alpha Rhythms of Neocortex and Thalamus 44
3.3 Beta/Gamma Activity of the Neocortex 46
3.4 Dc 50
4 Origin of the EEG/MEG II: Generators, Volume Conduction and Source Estimation 50
5 Localisation Methods Applied to Spontaneous Oscillatory Activities 53
5.1 EEG-Correlated fMRI 54
6 Conclusions 54
References 55
3 The Basics of Functional Magnetic Resonance Imaging 59
1 The Basics of MR Imaging 59
1.1 Spins in an External Magnetic Field 59
1.2 The Magnetic Resonance Effect 60
1.3 Spatial Encoding in MR Imaging 60
1.4 Relaxation Times T1 and T2 63
1.5 Gradient Echoes and the Relaxation Time T2* 64
1.6 k-Space 66
1.7 Echo Planar Imaging (EPI) 67
1.8 Spin Echoes 68
1.9 The Specific Absorption Rate (SAR) 69
2 The Cerebral Blood Flow (CBF) 70
2.1 Definition, Order of Magnitude, Measurement 70
2.2 Arterial Spin Labelling Measurements 72
2.3 Labelling Methods 73
2.4 Quantification Problems in ASL 73
3 The Cerebral Blood Volume (CBV) 74
3.1 Definition, Order of Magnitude, Measurement 74
3.2 Contrast Agent-Based Methods 74
3.3 Contrast Agent-Free Method: Vascular Space Occupancy Measurement 76
4 The BOLD Effect and Functional MRI 77
References 80
4 Locally Measured Neuronal Correlates of Functional MRI Signals 83
1 Blood Oxygenation Level Dependent Functional MRI Signals 83
2 Synaptic Activity and Local Field Potentials Spiking and Multiunit Activity
3 Neurophysiological Activity and fMRI Signals: Time and Space 85
4 Neurophysiological Activity and fMRI Signals: Amplitude and Reliability 86
5 The Driving Force of the Haemodynamic Response: Synaptic or Spiking Activity? 88
6 Neuronal Correlates of Negative Bold Responses 93
7 Neuronal Correlates of Spontaneous Fluctuations in fMRI Signals 94
8 Neurovascular Coupling 95
9 Summary 98
References 99
5 What Can fMRI Add to the ERP Story? 103
1 Introduction 103
2 ERP Generator Localisation 105
3 The Inverse Problem of EEG 105
4 Does fMRI Help to Solve the Inverse Problem? 108
5 Further Aspects 110
5.1 Serial Processing vs. Parallel and Reciprocal Network Activity 110
5.2 Subcortical Processing 110
6 Conclusions 111
References 111
6 The Added Value of EEG–fMRI in Imaging Neuroscience 116
1 Introduction 116
2 The EEG–fMRI Integrated Source Space 117
3 Integration Strategies for EEG–fMRI Studies 121
4 Illustration of the Integration of fMRI and EEG in the Temporal Domain 122
5 Illustration of the Integration of fMRI and EEG in the Spatial Domain 123
6 Discussion 127
References 129
Part II Technical and Methodological Aspects of Combined EEG–fMRI Experiments 132
7 EEG Instrumentation and Safety 133
Abbreviations 133
1 Introduction 133
2 EEG Instrumentation 134
2.1 Electrodes 134
2.2 EEG Recording System 136
2.3 RF Emissions 140
2.4 Miscellaneous Factors 141
2.5 Summary 142
3 Safety 142
3.1 Safety Limits 142
3.2 Static Field 143
3.3 Gradient Fields 143
3.4 Eddy Currents 144
3.5 RF Fields 144
3.6 Implanted Electrodes 147
3.7 Summary 148
References 149
8 EEG Quality: Origin and Reduction of the EEG Cardiac-Related Artefact 152
1 Introduction 152
2 Characteristics of the Pulse Artefact 153
3 Origin of the Pulse Artefact, Simulations and Modelling 156
4 Reducing the Pulse Artefact Using Waveform Removal Approaches 159
5 Removing the Pulse Artefact Using Spatial Pattern Removal Approaches 162
6 Evaluation of Pulse Artefact Removal Approaches 165
7 Conclusions 165
References 166
9 EEG Quality: The Image Acquisition Artefact 169
Abbreviations 169
1 Origin of the Image Acquisition Artefact 169
2 Characteristics of the Image Acquisition Artefact 170
3 Avoiding Image Acquisition Artefacts: Interleaved EEG–fMRI Protocols 172
4 Reduction of Image Acquisition Artefacts 174
4.1 Reduction at the Source 174
4.2 Synchronisation of EEG and fMRI Data Acquisitions 175
5 Correction of the Image Acquisition Artefact Using EEG Post-Processing 177
5.1 Artefact Template Subtraction 177
5.2 Computing and Correcting Timing Errors 179
5.3 Temporal Principal Component Analysis 179
5.4 Independent Component Analysis 181
5.5 Filtering in the Frequency Domain 182
6 Evaluation of Correction Methods 182
References 185
10 Image Quality Issues 188
1 fMRI Pulse Sequences 188
2 GE-EPI 189
2.1 Image Blurring 189
2.2 Geometric Distortion 192
2.3 Signal Dropout 194
2.4 Image Ghosting 197
2.5 RF Interference 197
3 Other Sources of Image Artefact in fMRI 198
3.1 Bulk Head Motion 198
3.2 Physiological Noise 199
4 The Impact of EEG Recording on MR Image Quality 199
4.1 Main Static Magnetic Field (B 200
) Effects 200
4.2 Transverse Rotational Magnetic Field (B 201
) Effects 201
4.3 Impact on SNR 204
5 fMRI Quality Assurance (QA) 205
5.1 Quantification of SNR and Temporal SNR 205
5.2 The Weisskoff Test 207
5.3 Coherent Noise Testing 208
6 Summary and Conclusions 209
References 209
11 Specific Issues Related to EEG–fMRI at B > 3 T
1 Introduction 215
2 Safety Considerations 215
2.1 Physical Principles and Relevant Safety Guidelines 215
2.2 Safety Studies at High Fields 216
3 EEG Recording and Quality 220
3.1 Pulse-Related Artifact 222
3.2 Other Noise Sources at High Field 222
4 Image Quality 223
5 Example of an Application of EEG–fMRI at 7 T: Auditory Steady State Response (ASSR) 224
6 Conclusions 225
Appendix 1: The Multidimensional Kalman Adaptive Filtering Method 226
Appendix 2: The Open Hardware and Software Project. The High-Field One System for Real-Time EEG–fMRI 228
Main Design Features 229
References 231
12 Experimental Design and Data Analysis Strategies 235
1 Introduction 235
2 Data Acquisition and Experimental Design 236
2.1 Interleaved EEG and fMRI Acquisitions: Triggered and Sparse Scanning 237
2.2 Simultaneous EEG and fMRI Acquisitions: Continuous Scanning 239
2.3 Experimental Protocol 239
3 Analysis of Simultaneously Acquired EEG–fMRI Data 241
3.1 Model-Based Analysis of fMRI Time-Series Data 242
3.2 EEG-Derived GLM: Use of Event Onsets and Illustration in Epilepsy 246
3.3 EEG-Derived GLM: Parametric Design and Single Trial 249
3.4 EEG-Derived GLM: EEG Spectrum 250
3.5 Multivariate Analysis 253
4 EEG and fMRI Localisation: Modes of Integration 253
4.1 Comparison of Independently Derived Results 254
4.2 fMRI as a Spatial Constraint for EEG Source Reconstruction 254
4.3 Towards Symmetrical Models of EEG and fMRI Fusion 256
5 Unresolved Problems and Caveats 256
5.1 Relationship Between Neuronal Activity, EEG and fMRI Signals 257
5.2 Specific Issues Related to Spontaneous Brain Activity 258
5.3 The Impact of Data Acquisition and Processing Artefacts on fMRI Data Analysis 259
6 Summary and Outlook 261
References 261
Part III Applications of EEG–fMRI 272
13 Brain Rhythms 274
1 Considerations for the Study of Rest 274
1.1 Why Study the Resting State? 274
2 A Multimodal Approach to the Resting State 275
2.1 From Unimodal to Multimodal Studies of Rest 276
2.2 Endogenous Brain Oscillations in Healthy Subjects 277
2.3 Similar Electrical Oscillations, Different fMRI Networks 278
2.4 Similar fMRI Networks, Different Electrical Oscillations 280
2.5 Brain Oscillations and Networks During Sleep 281
2.6 Endogenous Brain Oscillations in Patients with Epilepsy 282
3 Linking Neuronal Oscillations to Haemodynamic Changes 282
4 Conclusion 283
References 284
14 Sleep 289
Abbreviations 289
1 FMRI in Sleep Research 289
1.1 Sleep 289
1.2 Imaging Sleep 292
1.3 EEG and fMRI in Sleep Research 293
2 fMRI During Sleep: Technical Challenges 295
2.1 General Issues with Sleep fMRI 296
2.2 More Specific Issues with Sleep fMRI 298
2.3 Possible Solutions 300
3 FMRI in Sleep: Results 301
3.1 Spontaneous Sleep 301
3.2 Sensory Processing During Sleep 306
3.3 Animal Data 310
4 Summary and Outlook 311
References 312
15 EEG–fMRI in Adults with Focal Epilepsy 317
1 Introduction 317
2 Interictal EEG–fMRI 318
2.1 What Is an Interictal Spike? 318
2.2 Interictal Epileptiform Activity in Presurgical Assessment 319
2.3 Methodology 321
2.4 Relevance of the Observed BOLD Changes 324
2.5 Clinical Utility 326
2.6 The Influence of Lesions 328
3 Ictal EEG–fMRI 329
3.1 Limitations of Ictal EEG–fMRI 330
3.2 Detection of Ictal Activity 332
3.3 General Linear Model Building 333
3.4 Application of Ictal EEG–fMRI 333
4 Conclusions 334
References 335
16 EEG–fMRI in Idiopathic Generalised Epilepsy (Adults) 340
1 Idiopathic Generalised Epilepsy 340
1.1 Definition and Classification 340
1.2 The EEG in Idiopathic Generalised Epilepsy 341
2 Mechanisms of Generalised Spike and Wave in Idiopathic Generalised Epilepsy 341
3 EEG–fMRI in Human IGE 342
3.1 Early EEG–fMRI Studies 342
3.2 Overview of EEG–fMRI Data 343
4 Structures and Networks: Future Directions for EEG–fMRI in IGE 351
5 Conclusion 352
References 353
17 EEG–fMRI in Children with Epilepsy 355
Abbreviations 355
1 EEG–fMRI in Children with Epilepsy 355
2 Methodological Issues Specific to Paediatric EEG–fMRI Studies 356
2.1 Patient Selection and Scanning 356
2.2 Modelling IED-Related BOLD Changes in Children: Variability and Developmental Changes 356
3 Results of EEG–fMRI Studies in Paediatric Epilepsy 357
3.1 Idiopathic Focal Epilepsies 357
3.2 Symptomatic and Cryptogenic Focal Epilepsies 359
3.3 Epileptic Encephalopathies 363
3.4 Idiopathic Generalised Epilepsies 364
4 Summary and 365
Future Perspectives 365
References 366
18 Combining EEG and fMRI in Pain Research 370
1 Introduction 370
2 Combining EEG and fMRI in Pain Research: General Issues 372
3 Combining EEG and fMRI in Pain Research: Practical Issues 375
3.1 Selectivity of the Nociceptive Input in EEG–fMRI Studies 375
3.2 Delivery of Nociceptive Stimuli in the EEG–fMRI Environment 376
3.3 Experimental Design 377
4 Studies Combining EEG and fMRI in Pain Research 378
5 Future Directions: EEG-Driven Analysis of fMRI BOLD Responses to Nociceptive Stimulation 380
5.1 Single-Trial Estimation of the Magnitude of Stimulus-Evoked EEG Responses 381
5.2 Correlation Between EEG and fMRI Responses at Single-Trial Level 382
References 386
19 Simultaneous EEG and fMRI of the Human Auditory System 390
1 Introduction 390
2 Specifics of Auditory Recordings 391
2.1 Interference of the Static Magnetic Field 391
2.2 Interference of Transient Magnetic Fields 392
2.3 BOLD Response to Scanner Noise 392
2.4 Sparse Sampling 393
2.5 Silent fMRI Acquisition 394
2.6 Adjusting Auditory Stimulus Frequencies 394
3 Simultaneous EEG and fMRI in Auditory Experiments 396
4 Low-Noise fMRI Sequences for Simultaneous Experiments 397
5 Conclusions 400
References 400
20 Visual System 405
1 Simultaneous EEG–fMRI of the Visual System: Signal Quality 405
2 fMRI-Informed EEG of the Visual System 406
2.1 Localising Visual Evoked Potentials 407
2.2 Visual Attention and Other Cognitive Processes 408
3 EEG-Informed fMRI of the Visual System 410
3.1 Spontaneous EEG Oscillations 411
3.2 Task-Related EEG Activity 413
4 Uninformed EEG–fMRI and Other Approaches 414
4.1 Event-Related Oscillations 414
4.2 Visual Attention and Other Cognitive Processes 414
5 Investigating Neurovascular Coupling in the Visual System by EEG–fMRI 415
6 Outlook 417
References 418
21 Cognition 422
1 Advantages and Disadvantages of Simultaneous EEG–fMRI Recordings of Cognitive Functions 422
2 Cognitive Functions 423
2.1 Attention 423
2.2 Executive Functions 431
2.3 Memory 441
3 Limitations and Outlook 442
References 445
22 Neuronal Models for EEG–fMRI Integration 454
1 EEG and fMRI Integration 454
2 Neuronal Model of EEG–fMRI Integration 455
2.1 Dimensional Analysis 455
2.2 Modelling Activations 457
2.3 Effect of Neuronal Activation on BOLD 458
2.4 Effect of Neuronal Activation on EEG 458
3 Empirical Evidence for the Model 460
4 Summary 463
References 464
23 BOLD Response and EEG Gamma Oscillations 466
1 Introduction 466
2 Methodical Issues 467
3 Gamma Activity and BOLD Response 469
3.1 Co-variation of High-Frequency Oscillations and the BOLD Signal 469
3.2 Gamma Activity and BOLD Response: Variation Across Subjects 473
3.3 Gamma Activity and BOLD Response: Further Reports 475
3.4 Outlook: Single-Trial Coupling of Gamma Activity and BOLD Response 478
4 Conclusions 478
References 480
24 EEG–fMRI in Animal Models 485
1 Introduction 485
2 Advantages of EEG–fMRI in Animal Models 487
3 Limitations and Technical Challenges of EEG–fMRI in Animal Models 488
4 Anaesthesia 488
5 Movement: Curarisation and Habituation 490
6 Physiology 490
7 MR-Compatible Electrodes 491
8 EEG Artefacts and Artefact Removal 492
9 Data Analysis 492
10 Applications of Simultaneous EEG–fMRI in Animals 498
11 Epilepsy 499
12 Absence Seizure Models 499
13 Generalised Tonic-Clonic Seizure Models 500
14 Partial Seizure Models 500
15 Sleep 501
16 Sensorimotor Stimulation Models 502
17 The Electrophysiological Substrates of the BOLD Effect: Simultaneous Microelectrode EEG Recordings and fMRI 502
18 Future Directions 503
19 Conclusions 504
References 504
25 EEG–fMRI Information Fusion: Biophysics and Data Analysis 510
1 Introduction 510
2 EEG–fMRI Information Fusion: Limitations 511
2.1 Neurovascular Coupling and Decoupling 511
2.2 Experimental Limitations 512
3 EEG–fMRI Information Fusion: Solutions 513
3.1 Information Fusion: Definition 513
3.2 Asymmetrical vs. Symmetrical Approaches 514
3.3 EEG to fMRI Approaches 515
3.4 fMRI to EEG Approaches 516
3.5 Towards Symmetrical EEG–fMRI Approaches 517
4 Conclusion 521
References 521
Outlook 526
Index 528