APPLICATION OF DIPOLE LOCALIZATION METHODS TO SOURCE IDENTIFICATION OF HUMAN EVOKED POTENTIALS *

Attempts to specify the sources of evoked potentials (EPs) recorded from the human scalp have relied upon evidence from a variety of approaches, including studies of scalp topography, analyses of lesion effects, cortical surface and intracranial recordings in humans, and similar experiments in animals.’-’ In this paper I review the application of quantitative dipole localization methods derived from electrical field theory to the problem of E P source identification. My main objective is not to present the technical details of such method^,^' but to illustrate their value and limitations by applying them to empirical EP data. Applications of electrical field theory to the identification of electrical sources in the human body can be divided into two broad categories termed the “forward” and “inverse” problems. The forward problem is to calculate the potential field distribution over the surface of a volume conductor generated by electrical sources of known location and configuration in the volume conductor. Based on the work of Helmholtz,’ Wilson and Bayley’ presented a method for calculating the potential field on the surface of a homogeneous spherical volume conductor generated by a dipole source of arbitrary location and orientation in the sphere.? A number of EP and EEG investigators have used forward-problem approaches related to that of Wilson and Bayley to calculate the surface potential fields generated by theoretical sources proposed t o account for various EEG and E P p h e n ~ m e n a . ’ ~ ’ ~ The inverse problem is to calculate the sources within a volume conductor given the empirical potential field on the surface. Without additional information, the inverse problem is mathematically ill-posed and has no unique solution. Because the potential fields of different sources in a volume conductor sum linearly (Helmholtz’ principle of superposition), a given surface potential field could be produced by any

[1]  H. Helmholtz.  Ueber einige Gesetze der Vertheilung elektrischer Ströme in körperlichen Leitern mit Anwendung auf die thierisch‐elektrischen Versuche , 1853 .

[2]  M A B BRAZIER,et al.  The electrical fields at the surface of the head during sleep. , 1949, Electroencephalography and clinical neurophysiology.

[3]  F. N. Wilson,et al.  The Electric Field of an Eccentric Dipole in a Homogeneous Spherical Conducting Medium , 1950, Circulation.

[4]  R.N.Dej.,et al.  The Cerebral Cortex of Man , 1951, Neurology.

[5]  C. V. Nelson,et al.  Determination of the Resultant Dipole of the Heart from Measurements on the Body Surface , 1954 .

[6]  J C SHAW,et al.  Potential distribution analysis. II. A theoretical consideration of its significance in terms of electrical field theory. , 1955, Electroencephalography and clinical neurophysiology.

[7]  J. Shaw,et al.  Potential distribution analysis. I. A new technique for the analysis of electrophysiological phenomena. , 1955, Electroencephalography and clinical neurophysiology.

[8]  C. D. Geisler,et al.  The surface EEG in relation to its sources , 1961 .

[9]  R Plonsey,et al.  Limitations on the equivalent cardiac generator. , 1966, Biophysical journal.

[10]  D. A. Driscoll,et al.  Current Distribution in the Brain From Surface Electrodes , 1968, Anesthesia and analgesia.

[11]  W. Ritter,et al.  The sources of auditory evoked responses recorded from the human scalp. , 1970, Electroencephalography and clinical neurophysiology.

[12]  R. E. Marshall,et al.  Polarities and field configurations of the vertex components of the human auditory evoked response: a reinterpretation. , 1971, Electroencephalography and clinical neurophysiology.

[13]  D L Jewett,et al.  The effect of media inhomogeneities upon intracranial electrical fields. , 1972, IEEE transactions on bio-medical engineering.

[14]  M R Schneider,et al.  A multistage process for computing virtual dipolar sources of EEG discharges from surface information. , 1972, IEEE transactions on bio-medical engineering.

[15]  T. Tsumoto,et al.  Analysis of somatosensory evoked potentials to lateral popliteal nerve stimulation in man. , 1972, Electroencephalography and clinical neurophysiology.

[16]  Herbert G. Vaughan,et al.  Chapter 4 – The Analysis of Scalp-Recorded Brain Potentials , 1974 .

[17]  S. Hillyard,et al.  Human auditory evoked potentials. I. Evaluation of components. , 1974, Electroencephalography and clinical neurophysiology.

[18]  S. Butler,et al.  The localization of equivalent dipoles of EEG sources by the application of electrical field theory. , 1975, Electroencephalography and clinical neurophysiology.

[19]  G. Barrett,et al.  A paradox in the lateralisation of the visual evoked response , 1976, Nature.

[20]  R. Cracco,et al.  Scalp recorded auditory evoked potentials and sonomotor responses: an evaluation of components and recording techniques. , 1977, Electroencephalography and clinical neurophysiology.

[21]  W. Ritter,et al.  The scalp topography of potentials in auditory and visual discrimination tasks. , 1977, Electroencephalography and clinical neurophysiology.

[22]  Dietrich Lehmann,et al.  Evaluation of Methods for Three-Dimensional Localization of Electrical Sources in the Human Brain , 1978, IEEE Transactions on Biomedical Engineering.

[23]  R D Sidman,et al.  A method for localization of sources of human cerebral potentials evoked by sensory stimuli. , 1978, Sensory processes.

[24]  W C Wiederholt,et al.  Short-latency somatosensory evoked potentials. , 1978, Archives of neurology.

[25]  T. Allison,et al.  THE FUNCTIONAL NEUROANATOMY OF EVENT RELATED POTENTIALS , 1978 .

[26]  G G Celesia,et al.  Somatosensory evoked potentials recorded directly from human thalamus and Sm I cortical area. , 1979, Archives of neurology.

[27]  W. Oldendorf.  Cost‐effectiveness and role of routine skull radiography , 1979, Neurology.

[28]  G Cheron,et al.  Somatosensory evoked potentials to finger stimulation in healthy octogenarians and in young adults: wave forms, scalp topography and transit times of parietal and frontal components. , 1980, Electroencephalography and clinical neurophysiology.

[29]  D H Fender,et al.  Methods for the localization of electrical sources in the human brain. , 1980, Progress in brain research.

[30]  J. Desmedt,et al.  Functional organization of far-field and cortical components of somatosensory evoked potentials in normal adults , 1980 .

[31]  W. Ritter,et al.  Topographic analysis of auditory event-related potentials. , 1980, Progress in brain research.

[32]  J. P. Ary,et al.  Location of Sources of Evoked Scalp Potentials: Corrections for Skull and Scalp Thicknesses , 1981, IEEE Transactions on Biomedical Engineering.

[33]  R. Cracco,et al.  Scalp-recorded short latency cortical and subcortical somatosensory evoked potentials to peroneal nerve stimulation. , 1981, Electroencephalography and clinical neurophysiology.

[34]  D Lehmann,et al.  Intracerebral and scalp fields evoked by hemiretinal checkerboard reversal, and modeling of their dipole generators. , 1982, Advances in neurology.

[35]  P. Perot,et al.  SCALP‐RECORDED SOMATOSENSORY EVOKED POTENTIALS TO STIMULATION OF NERVES IN THE LOWER EXTREMITIES AND EVALUATION OF PATIENTS WITH SPINAL CORD TRAUMA * , 1980, Annals of the New York Academy of Sciences.

[36]  T Allison,et al.  SCALP AND CORTICAL RECORDINGS OF INITIAL SOMATOSENSORY CORTEX ACTIVITY TO MEDIAN NERVE STIMULATION IN MAN * , 1980, Annals of the New York Academy of Sciences.

[37]  J. Kimura,et al.  SHORT‐LATENCY SOMATOSENSORY EVOKED POTENTIALS FOLLOWING MEDIAN NERVE STIMULATION , 1980 .