Emulation of somatosensory evoked potential (SEP) components with the 3-shell head model and the problem of 'ghost potential fields' when using an average reference in brain mapping.

In brain topographic mapping, the putative location and orientation in the head space of neural generators are currently inferred from the features of negative and positive scalp potential fields. This procedure requires the use of a fairly neutral reference. The frequently advocated average reference creates problems because its effect is not merely to change a (steady) zero reference level, but to dynamically zero-center all scalp potentials at each latency. Ghost potential fields are thus created at the latencies for which the integral of scalp recorded potentials differs from zero. These distortions of brain mapping have been analyzed with a true 3-shell head model in conjunction with the emulation of SEP components. In the head model, surface potential fields generated by dipoles or dipole sheets of various depths and orientations were computed either over the north hemisphere, so as to emulate scalp recorded SEP components, or over the entire equivalent head sphere. The spurious effects of the average reference are shown to occur because it is computed from a limited number of (scalp) electrodes which fail to survey the bottom half of the head.

[1]  S. Zeki.  Functional specialisation in the visual cortex of the rhesus monkey , 1978, Nature.

[2]  F. Perrin,et al.  Sequential mapping favours the hypothesis of distinct generators for Na and Pa middle latency auditory evoked potentials. , 1988, Electroencephalography and clinical neurophysiology.

[3]  M Nakamura,et al.  Elimination of EKG artifacts from EEG records: a new method of non-cephalic referential EEG recording. , 1987, Electroencephalography and clinical neurophysiology.

[4]  F. Offner,et al.  The EEG as potential mapping: the value of the average monopolar reference. , 1950, Electroencephalography and clinical neurophysiology.

[5]  F. Perrin,et al.  Mapping of scalp potentials by surface spline interpolation. , 1987, Electroencephalography and clinical neurophysiology.

[6]  Y. Toyokura,et al.  The initial positive component of the scalp-recorded somatosensory evoked potential in normal subjects and in patients with neurological disorders. , 1978, Electroencephalography and clinical neurophysiology.

[7]  C Tomberg,et al.  Mapping somatosensory evoked potentials to finger stimulation at intervals of 450 to 4000 msec and the issue of habituation when assessing early cognitive components. , 1989, Electroencephalography and clinical neurophysiology.

[8]  O Bertrand,et al.  Sequential colour mapping system of brain potentials. , 1985, Computer methods and programs in biomedicine.

[9]  Dietrich Lehmann,et al.  Spatial analysis of evoked potentials in man—a review , 1984, Progress in Neurobiology.

[10]  O Bertrand,et al.  A theoretical justification of the average reference in topographic evoked potential studies. , 1985, Electroencephalography and clinical neurophysiology.

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

[12]  J E Desmedt,et al.  Color imaging of parietal and frontal somatosensory potential fields evoked by stimulation of median or posterior tibial nerve in man. , 1985, Electroencephalography and clinical neurophysiology.

[13]  J. Desmedt,et al.  New method for titrating differences in scalp topographic patterns in brain evoked potential mapping. , 1989, Electroencephalography and clinical neurophysiology.

[14]  F. Duffy,et al.  Clinical value of topographic mapping and quantified neurophysiology. , 1989, Archives of neurology.

[15]  P. Nunez,et al.  Electric fields of the brain , 1981 .

[16]  G. Cheron,et al.  Non-cephalic reference recording of early somatosensory potentials to finger stimulation in adult or aging normal man: differentiation of widespread N18 and contralateral N20 from the prerolandic P22 and N30 components. , 1981, Electroencephalography and clinical neurophysiology.

[17]  D. Lehmann.  Multichannel topography of human alpha EEG fields. , 1971, Electroencephalography and clinical neurophysiology.

[18]  K. Maurer,et al.  Topographic Brain Mapping of EEG and Evoked Potentials , 1989, Springer Berlin Heidelberg.

[19]  F Mauguiere,et al.  Separate generators with distinct orientations for N20 and P22 somatosensory evoked potentials to finger stimulation? , 1986, Electroencephalography and clinical neurophysiology.

[20]  R. Cracco,et al.  Short latency SEPs to median nerve stimulation: comparison of recording methods and origin of components. , 1981, Electroencephalography and clinical neurophysiology.

[21]  A. Ebner,et al.  Frontal and parietal components of enhanced somatosensory evoked potentials: a comparison between pathological and pharmacologically induced conditions. , 1988, Electroencephalography and clinical neurophysiology.

[22]  H. Spekreijse,et al.  Mathematical dipoles are adequate to describe realistic generators of human brain activity , 1988, IEEE Transactions on Biomedical Engineering.

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

[24]  F. Plum.  Handbook of Physiology. , 1960 .

[25]  G Cheron,et al.  Central somatosensory conduction in man: neural generators and interpeak latencies of the far-field components recorded from neck and right or left scalp and earlobes. , 1980, Electroencephalography and clinical neurophysiology.

[26]  F Mauguière,et al.  Astereognosis and dissociated loss of frontal or parietal components of somatosensory evoked potentials in hemispheric lesions. Detailed correlations with clinical signs and computerized tomographic scanning. , 1983, Brain : a journal of neurology.

[27]  A Rémond,et al.  EEG field mapping. , 1978, Electroencephalography and clinical neurophysiology.

[28]  Ronald P. Lesser,et al.  Subcortical somatosensory evoked potentials to median nerve stimulation. , 1983, Brain : a journal of neurology.

[29]  C C Wood,et al.  Electrical sources in human somatosensory cortex: identification by combined magnetic and potential recordings. , 1985, Science.

[30]  J. Desmedt,et al.  Thalamic pain syndrome of Dejérine-Roussy. Differentiation of four subtypes assisted by somatosensory evoked potentials data. , 1988, Archives of neurology.

[31]  M G Marciani,et al.  Non-invasive evaluation of input-output characteristics of sensorimotor cerebral areas in healthy humans. , 1987, Electroencephalography and clinical neurophysiology.

[32]  J. Desmedt,et al.  Bilateral somatosensory evoked potentials in four patients with long‐standing surgical hemispherectomy , 1989, Annals of neurology.

[33]  C Tomberg,et al.  Mapping early somatosensory evoked potentials in selective attention: critical evaluation of control conditions used for titrating by difference the cognitive P30, P40, P100 and N140. , 1989, Electroencephalography and clinical neurophysiology.

[34]  S. Tsuji,et al.  Frontal distribution of early cortical somatosensory evoked potentials to median nerve stimulation. , 1988, Electroencephalography and clinical neurophysiology.

[35]  L. Kaufman,et al.  On the relation between somatic evoked potentials and fields. , 1981, The International journal of neuroscience.

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

[37]  R. Cracco,et al.  Somatosensory evoked potential in man: far field potentials. , 1976, Electroencephalography and clinical neurophysiology.

[38]  A S Gevins,et al.  Neurocognitive pattern analysis of a visuospatial task: rapidly-shifting foci of evoked correlations between electrodes. , 1985, Psychophysiology.

[39]  J. Desmedt,et al.  Bit-mapped colour imaging of the potential fields of propagated and segmental subcortical components of somatosensory evoked potentials in man. , 1984, Electroencephalography and clinical neurophysiology.

[40]  R. Rodnitzky,et al.  Clinical correlates of abnormal P14 in median SEPs , 1986, Neurology.

[41]  R Coppola,et al.  Computer generation of surface distribution maps of measures of brain activity. , 1982, Computers in biology and medicine.

[42]  F Mauguière,et al.  Neural generators of N18 and P14 far-field somatosensory evoked potentials studied in patients with lesion of thalamus or thalamo-cortical radiations. , 1983, Electroencephalography and clinical neurophysiology.

[43]  D. Lehmann,et al.  Reference-free identification of components of checkerboard-evoked multichannel potential fields. , 1980, Electroencephalography and clinical neurophysiology.

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

[45]  C Tomberg,et al.  Inadequacy of the average reference for the topographic mapping of focal enhancements of brain potentials. , 1990, Electroencephalography and clinical neurophysiology.

[46]  J E Desmedt,et al.  Bit-mapped color imaging of human evoked potentials with reference to the N20, P22, P27 and N30 somatosensory responses. , 1987, Electroencephalography and clinical neurophysiology.

[47]  R. L. Nó,et al.  Action potential of the motoneurons of the hypoglossus nucleus. , 1947 .