Arden V. Nelson

Digital zero-phase-shift filtering of short-latency somatosensory evoked potentials

Short-latency somatosensory potentials evoked by median nerve stimulation were averaged after analogue bandpass of 30-3000 Hz and then filtered by a zero-phase-shift digital filter with bandpass of 200-1500 Hz. Both near- and far-field potentials recorded by scalp to scalp, ear and extracephalic references were enhanced, without temporal distortion or the introduction of spurious peaks. Components were identified at the same or similar peak latencies as reported by other investigators. Zero-phase-shift digital filtering may increase the usefulness of recording short-latency somatosensory potentials.

Unilateral Temporal Lobe Lesions Alter P300 Scalp Topography

Event related potentials were recorded from patients with unilateral temporal lobe lesions and healthy volunteers. Subjects were required to silently count on infrequent target tone interspersed among presentations of a non-target tone, with an interval between tones that was relatively long and variable (6-10s). Under these task conditions, the patients were found to have P300 amplitudes that were smaller on the lesioned side relative to the non-lesioned side. This finding is interpreted as evidence that temporal lobe lesions affect the configuration of intracranial sources generating the P300 component of event-related potentials.

Barbiturate Anticonvulsants: A Neuropsychological and Quantitative Electroencephalographic Study

We studied 11 epileptic children aged 7 to 14 years with quantitative electroencephalographic (EEG) and neuropsychological tests, both on and off the barbiturate anticonvulsants phenobarbital and mephobarbital, comparing them to 13 controls matched for age and IQ who received testing at similar intervals. Neuropsychological tests employed were the Wechsler Intelligence Scale for Children-Revised (WISC-R), Bender-Gestalt, controlled oral word association test (COWAT), selected subtests of the Wechsler Memory Scale-Revised, Purdue Peg Board, Stroop Test, Trail Making Test, Wide Range Achievement Test-Revised, and Achenbach Behavior Rating Scale. There was no difference between on- and off-drug quantitative EEG in percentage power of any frequency band between 0.6 and 32 Hz. Neuropsychological data from all 11 subjects were analyzed with a two-factor analysis of variance with repeated measures on the time factor. The only difference from controls was on the Stroop Test. Parents reported clear behavioral changes in 6 of 11 subjects, but in 4 of these children the behavioral changes were sufficiently mild that parents chose to continue the barbiturate anticonvulsants: irritability, oppositional attitude, and overactivity were described. Mephobarbital was reported by parents to cause less severe problems than phenobarbital in subjects who had taken both barbiturate anticonvulsants. Barbiturate anticonvulsants have no effect on quantitative EEG and limited effects on neuropsychological tests in school-aged children. (J Child Neurol 1997;12:169-171).

The topography of muscle activity in quantitative EEG

Ten normal preadolescent subjects were studied on three occasions with quantitative EEG topography: two sessions recorded EEG that was free of artifact, but during the third the subjects were instructed to clench their teeth and tighten their faces to produce muscle artifact. The sessions were then compared for stability of various frequencies at standard scalp electrode sites. The posterior electrodes were stable among sessions for frequencies up to 24 Hz; the anterior electrodes were less stable, and above 24 Hz there were no stable electrode sites. Muscle artifact contaminates anterior electrode sites more than posterior sites, making the posterior scalp electrodes superior for studying beta activity in quantitative EEG. Frequencies above 24 Hz are contaminated at all sites and therefore cannot be assessed reliably in the presence of muscle artifact.

Topographical mapping of brain electrical activity

Current topographical mapping methods and problems associated with mapping are reviewed, and one approach for improving the spatial resolution of scalp recorded EEGs is detailed. In particular, techniques for interpolating the potential distribution and estimating the surface Laplacian from multichannel data are presented and applied to human evoked potential data. Although developed for electroencephalographic data, these spline algorithms can be applied to a variety of fields where visualization of spatial information is desired.<<ETX>>

Spline generated Laplacians of evoked potentials

The use of spline-generated Laplacians was investigated for several types of evoked potentials. Potentials were recorded from several subjects and spline-fitted to a sphere generated, using nonlinear regression techniques, from digitized head coordinate values. This preliminary study confirms that the topological maps of the surface Laplacian are much better in defining surface differences than potential maps.<<ETX>>

Comparison of the Laplacian with classical recording methods in coherence analysis of EEG

A bshuctThe EEG as classically recorded is influenced by the activity at the reference electrode. The nearest-neighbor Laplacian is a method that removes the ef€ect of the reference electrode by representing the current activity under the recording electrode. In this study coherence was obtained from EEG recorded from four Merent scalp Imtions. During the recording sections the subjects engaged in different cognitive tasks. The coherence of the Laplacian recordings showed sharper peaks than the coherence from the referential or bipolar recordings. Differences were found between the tasks for all SubjeaS.

Differences in EEG properties resulting from analysis using nearest-neighbor Laplacian, referencial and bipolar recording methods

Discusses the differences in EEG spectra and coherencies that are found when using nearest-neighbor Laplacian, referencial and bipolar recording methods. These differences are caused in part by the different spatial resolutions of the three methods.<<ETX>>

Spatial empirical orthogonal functions of multichannel visual evoked response

Simulated and real visual evoked EEG data were used to study the use of empirical orthogonal functions to describe spatial EEG properties. Sixteen channels of EEG data were recorded from the back of the head during visual checkerboard stimulation. From these data the sum of cross products was obtained at discrete time intervals before and after the stimulus. The empirical orthogonal functions are the eigenvectors of the cross product matrix and their coefficients are the square roots of the corresponding eigenvalues.<<ETX>>