Clinical Electrophysiology of the Somatosensory Cortex: A Combined Study Using Electrocorticography, Scalp-EEG, and Magnetoencephalography

1. Introduction.- 1.1. Functional Anatomy of Human Somatosensory Cortex.- 1.1.1. Clinical Importance.- 1.1.2. Methods to Study Functional Anatomy of Human Somatosensory Cortex.- 1.1.2.1. Direct Cortical Stimulations.- 1.1.2.2. Somatosensory Evoked Potentials on Electrocorticography.- 1.1.2.3. Somatosensory Evoked Potentials on Scalp-EEG.- 1.1.2.4. Somatosensory Evoked Fields on Magnetoencephalography.- 1.1.3. The Neuronal Sources of Somatosensory Evoked Responses.- 1.2. Somatotopy of Human Somatosensory Cortex.- 1.2.1. Current Concepts Concerning the Somatotopic Organization of Somatosensory Cortex.- 1.2.2. Clinical Importance.- 1.2.3. Methods to Study Somatotopy of Human Somatosensory Cortex.- 1.2.3.1. Direct Cortical Stimulations.- 1.2.3.2. Somatosensory Evoked Potentials on Electrocorticography.- 1.2.3.3. Somatosensory Evoked Potentials on Scalp-EEG.- 1.2.3.4. Somatosensory Evoked Fields on Magnetoencephalography.- 2. General Methodology.- 2.1. Neurogenesis of ECoG, Scalp-EEG, and MEG.- 2.2. Biophysical Laws of EEG and MEG.- 2.2.1. Forward and Inverse Problem.- 2.2.2. Assumptions Concerning the Current Sources.- 2.2.3. Assumptions Concerning the Volume Conductor.- 2.2.4. Practical Outline of Dipole Modeling.- 2.3. Magnetoencephalography - Basic Concepts.- 2.3.1. Basic Principles of the Procedure.- 2.3.2. Instrumentation.- 2.3.3. Magnetic Shielding.- 2.3.4. Differences Between Scalp-EEG and MEG.- 2.4. Cortical Stimulations.- 2.4.1. Subdural Grid Electrodes.- 2.4.2. Stimulus Parameters.- 2.4.3. Neurophysiological Effects of Cortical Stimulations.- 2.4.4. General Testing Procedure.- 3. Spatiotemporal Modeling on ECoG, Scalp-EEG, and MEG.- 3.1. Motivation.- 3.2. Simulation Study.- 3.3. Basic Goals of Spatiotemporal Modeling.- 3.4. Principal Component Analysis.- 3.4.1. Introduction.- 3.4.2. Methods.- 3.5. Combination of Principal Component Analysis and Biophysical Modeling.- 3.6. Multiple Dipole Modeling.- 3.6.1. Introduction.- 3.6.2. Methods.- 3.6.2.1. Forward Problem.- 3.6.2.2. Inverse Problem.- 3.7. Practical Outline of Spatiotemporal Modeling.- 3.8. Spatiotemporal Modeling as Outlined on Two Typical Examples.- 3.8.1. Modeling of Somatosensory Evoked Magnetic Fields.- 3.8.2. Modeling of the Human Epileptic Spike Complex.- 3.9. Limitations of the Procedure.- 3.9.1. Limitations of Principal Component Analysis.- 3.9.2. Limitations of Multiple Dipole Modeling.- 4. Functional Anatomy of Human Somatosensory Cortex.- 4.1. Methods.- 4.1.1. Cortical Stimulations - Median Nerve Somatosensory Evoked Potentials on Electrocorticography.- 4.1.1.1. Patients.- 4.1.1.2. Cortical Stimulations.- 4.1.1.3. Somatosensory Evoked Potentials on Electrocorticography.- 4.1.1.4. Correlation of Neuroelectric and Anatomical Data.- 4.1.1.5. Data Analysis.- 4.1.2. Median Nerve Somatosensory Evoked Potentials on Scalp-EEG.- 4.1.2.1. Subjects and Procedures.- 4.1.2.2. Correlation of Neuroelectric and Anatomical Data.- 4.1.2.3. Data Analysis.- 4.1.3. Median Nerve Somatosensory Evoked Fields on Magnetoencephalography.- 4.1.3.1. Subjects and Procedures.- 4.1.3.2. Correlation of Neuromagnetic and Anatomical Data.- 4.1.3.3. Data Analysis.- 4.2. Results.- 4.2.1. Cortical Stimulations - Median Nerve Somatosensory Evoked Potentials on Electrocorticography.- 4.2.1.1. Cortical Stimulations.- 4.2.1.2. Somatosensory Evoked Potentials - Data.- 4.2.1.3. Number of Sources.- 4.2.1.4. Results of Spatiotemporal Modeling.- 4.2.1.5. Results of Selected Patients.- 4.2.2. Median Nerve Somatosensory Evoked Potentials on Scalp-EEG.- 4.2.2.1. Data.- 4.2.2.2. Number of Sources.- 4.2.2.3. Results of Spatiotemporal Modeling.- 4.2.2.4. Results of Selected Subjects.- 4.2.3. Median Nerve Somatosensory Evoked Fields on Magnetoencephalography.- 4.2.3.1. Data.- 4.2.3.2. Number of Sources.- 4.2.3.3. Results of Spatiotemporal Modeling.- 4.2.3.4. Results of Selected Subjects.- 4.2.4. Comparison of ECoG, Scalp-EEG, and MEG.- 4.2.4.1. Comparison of the Raw Data for the Subjects as a Group.- 4.2.4.2. Comparison of Spatiotemporal Modeling for the Subjects as a Group.- 4.2.4.3. Comparison of ECoG and Scalp-EEG in a Selected Patient.- 4.2.4.4. Comparison of Scalp-EEG and MEG in a Selected Subject.- 4.3. Discussion.- 4.3.1. Cortical Stimulations - Median Nerve Somatosensory Evoked Potentials on Electrocorticography.- 4.3.1.1. Cortical Stimulations.- 4.3.1.2. Data.- 4.3.1.3. Source Localization Techniques.- 4.3.1.4. Spatiotemporal Modeling.- 4.3.1.5. The Neuronal Sources Underlying SEPs.- 4.3.1.6. Limitations of the Procedure.- 4.3.2. Median Nerve Somatosensory Evoked Potentials on Scalp-EEG.- 4.3.2.1. Data.- 4.3.2.2. Source Localization Techniques.- 4.3.2.3. Spatiotemporal Modeling.- 4.3.2.4. Neuronal Sources Underlying SEPs.- 4.3.2.5. Limitations of the Procedure.- 4.3.3. Median Nerve Somatosensory Evoked Fields on Magnetoencephalography.- 4.3.3.1. Data.- 4.3.3.2. Spatiotemporal Modeling.- 4.3.3.3. The Neuronal Sources Underlying SEFs.- 4.3.3.4. Functional Organization of Human Somatosensory Cortex.- 4.3.4. Comparison of ECoG, Scalp-EEG, and MEG.- 4.3.4.1. Comparison of ECoG and Scalp-EEG.- 4.3.4.2. Comparison of Scalp-EEG and MEG.- 4.3.4.3. Localization Accuracy of Scalp-EEG and MEG.- 4.3.4.4. Additional Information Revealed by Scalp-EEG and MEG.- 4.3.5. Considerations Concerning the Model.- 4.3.5.1. The Dipole Concept.- 4.3.5.2. Spatiotemporal Modeling - Modeling Assumptions and Neurophysiological Considerations.- 4.3.5.3. Spatiotemporal Modeling-Mathematical and Computational Considerations.- 4.3.6. Neurogenesis of the Human Somatosensory Evoked Response.- 4.3.6.1. The Primary Evoked Response.- 4.3.6.2. Neurogenesis of the N20-P30 Component-Activity Attributed to Area 3b.- 4.3.6.3. Neurogenesis of the P25-N35 Component-Activity Attributed to Area 1.- 5. Somatotopy of Human Somatosensory Cortex.- 5.1. Methods.- 5.1.1. Somatotopy as Studied with Cortical Stimulations and Somatosensory Evoked Potentials on Electrocorticography.- 5.1.1.1. Patients.- 5.1.1.2. Cortical Stimulations.- 5.1.1.3. Somatosensory Evoked Potentials Recorded on Electrocorticography.- 5.1.1.4. Correlation of Neuroelectric and Anatomical Data.- 5.1.1.5. Data Analysis.- 5.1.2. Somatotopy as Studied on Scalp-EEG.- 5.1.2.1. Subjects and Procedures.- 5.1.2.2. Correlation of Neuroelectric and Anatomical Data.- 5.1.2.3. Data Analysis.- 5.1.3. Somatotopy as Studied on Magnetoencephalography.- 5.1.3.1. Subjects and Procedures.- 5.1.3.2. Correlation of Neuromagnetic and Anatomical Data.- 5.1.3.3. Data Analysis.- 5.2. Results.- 5.2.1. Somatotopy as Studied with Cortical Stimulations and Somatosensory Evoked Potentials on Electrocorticography.- 5.2.1.1. Cortical Stimulations.- 5.2.1.2. Somatosensory Evoked Potentials - Data.- 5.2.1.3. Isopotential Maps for Median and Ulnar Nerve SEPs.- 5.2.1.4. Isopotential Maps for Digit SEPs.- 5.2.1.5. Isopotential Maps for Lip SEPs.- 5.2.1.6. Cortical Hand and Digit Representation.- 5.2.1.7. Cortical Lip Representation in Relation to Hand Representation.- 5.2.2. Somatotopy as Studied on Scalp-EEG.- 5.2.2.1. Data.- 5.2.2.2. Isopotential Maps for Median and Ulnar Nerve SEPs.- 5.2.2.3. Isopotential Maps for Digit SEPs.- 5.2.2.4. Cortical Hand and Digit Representation.- 5.2.3. Somatotopy as Studied on Magnetoencephalography.- 5.2.3.1. Data.- 5.2.3.2. Isofield Maps for Median, Ulnar Nerve and Digit SEFs.- 5.2.3.3. Cortical Hand and Digit Representation.- 5.2.4. Comparison of ECoG, Scalp-EEG, and MEG.- 5.2.4.1. General Comparison.- 5.2.4.2. Comparison of Somatotopy on ECoG and Scalp-EEG in a Selected Patient.- 5.2.4.3. Comparison of Somatotopy on Scalp-EEG and MEG in Two Selected Subjects.- 5.3. Discussion.- 5.3.1. Somatotopy as Studied with Cortical Stimulations and Somatosensory Evoked Potentials on Electrocorticography.- 5.3.1.1. Cortical Stimulations.- 5.3.1.2. Somatosensory Evoked Potentials - Data.- 5.3.1.3. Isopotential Maps.- 5.3.1.4. Somatotopy of Human Hand Somatosensory Cortex 151 5.3.1.5. Neuronal Sources in Human Hand Somatosensory Cortex.- 5.3.1.6. Somatotopy and Neuronal Sources of Lip Somatosensory Cortex.- 5.3.2. Somatotopy as Studied on Scalp-EEG.- 5.3.2.1. Data.- 5.3.2.2. Isopotential Maps.- 5.3.2.3. Somatotopy of Human Hand Somatosensory Cortex 157 5.3.2.4. Neuronal Sources in Human Hand Somatosensory Cortex.- 5.3.3. Somatotopy as Studied on Magnetoencephalography.- 5.3.3.1. Data.- 5.3.3.2. Isofield Maps.- 5.3.3.3. Somatotopy of Human Hand Somatosensory Cortex 162 5.3.3.4. Neuronal Sources in Human Hand.- Somatosensory Cortex.- 5.3.4. Comparison of ECoG, Scalp-EEG, and MEG.- 6. Clinical Implications.- 7. Summary.- 8. List of Abbreviations.- 9. References.