Clinical electrophysiology of the somatosensory cortex : a combined study using electrocorticography, scalp-EEG, and magnetoencephalography

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Clinical electrophysiology of the somatosensory cortex : a combined study using electrocorticography, scalp-EEG, and magnetoencephalography

Christoph Baumgartner

Springer-Verlag, c1993

  • Wien
  • New York

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Description and Table of Contents

Description

The functional anatomy of human somatosensory cortex is of both scientific and clinical interest. Scientifically, it provides insights in information processing in the human brain. Clinically, it helps to avoid neurological deficits by sparing essential brain regions during neurosurgical procedures adjacent to central fissure. In the present study the functional organization of the human somatosensory cortex was investigated with electrophysiological techniques using a combined approach of cortical stimulations and somatosensory evoked responses on electrocorticography, scalp-EEG, and magnetoencephalography. The spatiotemporal structure of the evoked response was studiedwith biophysical modeling techniqueswhich allowed identification of the three-dimensional intracerebral location, time activity, and interaction of the neuronal sources activated following peripheral somatosensory stimulation. Furthermore, the somatotopic organization ofhand and lip somatosensory cortex was investigated. The relative value of invasive (cortical stimulations and electrocorticography) and non-invasive (scalp-EEGand magnetoencephalography) was assessed. The combined use ofscalp-EEG and magnetoencephalography was useful to increase non-invasive localization accuracy. I want to thank several people who significantly contributed in completion of the present work. Univ. -Prof Dr. Luder Deecke, Chairman of the Neurological University Clinic, Vienna, Austria, supported me throughout my career at the Neurological University Clinic in Vienna since 1985. Dr. William W Sutherling, Associate Professor at the University of California, Los Angeles, who was my advisor during my stay from 1987-1989 at the Department ofNeurology, University of California, Los Angeles where most of the present work was done.

Table of Contents

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.

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