Combined Analysis of Horizontal and Vertical Optokinetic Nystagmus Reactions by Means of ENG and Brain Mapping (original) (raw)

Acta Oto-laryngologica, 1991

Abstract

ABSTRACT The horizontal and vertical optokinetic nystagmus is a jerk nystagmus which can be provoked by moving repetitive visual stimuli through the visual field in a horizontal or vertical plane. It can be evoked by the use of a tape drum or single point tracking stimuli. There is neurophysiological evidence that the ipsilateral occipital lobe controls persuit movements to the ipsilateral side. It is likely that each occipital lobe produces contralatera1 persuit movements under certain conditions. In a combined study we have investigated test persons with the polygraphic 5-channel- ENG technique and at the same time with the brain electrical activity mapping technique. Comparisons of scalp distributions of EEG derived potentials evoked in different experimental conditions during optokinetic stimulation provide us with useful information on how the different phases of the optokinetic tracking nystagmus is organized. It is well known that optic nerve and pathway activites can be recorded at widespread regions in the brain. Similar effects seem to hold for the motorcomponents in the various types of spatially organized optokinetic motor movements. Electrical activity was recorded as the potential difference between electrodes beside both eyes in horizontal and vertical positions. We regularly perform the electronystagmography as an office procedure on our neurootological patients. For the brain electrical activity mapping we apply a 16-channel-Picker-Schwartzer- Brain-Mapping-System containing an averager and a computer and a colour monitor of the type Picker-Schwartzer-Brain-Surveyer 11. The electrodes are placed on the scalp according to the international 10-20-electrode placement system, using the 16 positions Fpl, Fp2, F7, F3, F4, F8, T3, C3, C4, T4, T5, P3, P4, T6,Ol and 02. From the 16 EEG-channels the analogue signals undergo an AD-conversion. The brain surveyer then analyzes the EEG signals with respect to typical frequency and amplitude patterns of the superficial brain activity. The results are composed in maps of the calculated brain surface field power and/or frequency bands. The visually evoked potentials serve as a reference from a well known experiment towards new territories of equilibriometry . The VEP is performed binocularly. We then receive series of grand mean potential field maps after chessboard stimulation for the visually evoked potentials. The evaluation of the curves, of the latencies and the scalp locations give us a first topographical survey of this experimentally averaged EEG. Due to its long latency the PlOO component of the visual evoked potential is presumably of cortical origin and its skalp distribution after binocular and monocular stimulation provides a distribution pattern of the multidimensional statistical observations in the basic brain mapping. In these well known experiments spatial aspects of frequency characteristics power and phase angles of the spectral analysis can also be included into our calculations. Range or trajectories of positive and negative extreme values of the Delta Band, the Theta Band, the Alpha Band and the Beta Band can be calculated. Scalp distribution maps of locations of field positive and negative extreme values accumulated at times of maximal global field Acta Otolaryngol Downloaded from informahealthcare.com by Faculty of Medicine at Charles University on 11/21/12 For personal use only. 222 C.-F. Claussen et al. powers or at all sampling times can be calculated as band power of the 4 bands against an average reference or from 1 hemiscull against the other or other standards. All possible wave shapes first undergo a detection an clearing procedure for artefacts and then they are let into the calculation process. Before and after the visually evoked potentials we have performed a normal EEG with eyes closed and eyes open. The spontaneous scalp recorded electroencephalogram is always recorded for several minutes. The scalp distribution of the 4 frequency bands Delta (0-4 cps), Theta ( 4 7 cps), Alpha (8-12 cps), Beta (13-18 cps) is measured together with the field power at varying epochs between 2 and 60 s. Regularly the epochs are chosen for 30 s. Prior to the evaluation with mapping and histograms at the single electrode generators we have cleaned the 16 EEG curves from artefact rich segments. Then we systematically follow with the optokinetic orthogonal stimulus procedure known from our kite optogram. The optokinetic nystagmus is provoked by a single stimulus, which crosses the visual field of the patient in one direction and repeatedly returns from the same dwelling point. Therefore we use the computer regulated LED eyetrack. The stimulus moves over a segment of the horizon of 40". The patient is sitting on a rotatory chair with the head tightly kept in position. The monostimulus runs through 40" of the visual horizon and then disappears. As the next stimulus always follows at the same distance in the same plane and with the…

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