The contingent negative variation laterality and dynamics in antisaccade task in normal and unmedicated schizophrenic subjects

Contingent negative variation (CNV) topography, hemispheric asymmetry and time-course were investigated in healthy subjects and non-medicated paranoid schizophrenic patients in two antisaccade paradigms with the short (800-1000 ms) and long (1200-1400 ms) durations of the fixation period. EEG and electrooculogram (EOG) were recorded. Saccade characteristics and mean amplitudes of slow cortical potentials time-locked to peripheral target were analyzed in 23 healthy volunteers and 19 schizophrenic patients. Compared to healthy control subjects, schizophrenic patients had significantly slower antisaccades and committed significantly more erroneous saccades in the both antisaccade tasks. The prolongation of the fixation period resulted in noticeable decrease of error percent in patients group. The analysis of CNV time-course has revealed two distinct stages in both groups. The early CNV stage was represented by a negative wave with the maximal amplitude over midline fronto-central area, and the late stage was characterized by increased CNV amplitude at the midline and left parietal electrode sites. In healthy subjects the simultaneous activation of frontal and parietal areas was observed in the paradigm with the shorter fixation interval; the increase of the fixation period produced consecutive activation of these areas. Schizophrenic patients' CNV amplitude was generally smaller than that of healthy subjects. The most pronounced between-group differences of the negative shift amplitude were revealed at frontal electrode sites during the early CNV stage in both modifications of the antisaccade task. The deficit of frontal activation revealed in patients at the early stage of antisaccade preparatory set in both antisaccadic paradigms may be related to pathogenesis of paranoid schizophrenia.     

Perception and tonus

Abstract.— A review is given of the achievements of more than one hundred years of research concerning the influence of muscular tonus on the perceptual phenomena related to human spatial orientation. The tonal conditions of both the extrinsic eye muscles and the complex system of skeletal muscles have been shown to have decisive influence on "egocentric localization". The factual median is perceived as being displaced in the direction of the side of the body with greater tonus. This is the case whether the tonic asymmetry is experimentally induced or natural. Corresponding to this fact, a spot of light in the dark situated at the factual eye level will be perceived as being situated above the experienced eye level. The influence on egocentric localization exercised by prolonged fixation of greater or smaller parts of the muscular system (especially of the eye muscles) is pointed out. This "fixation effect" seems to be in accordance with conceiving the postural system of the body by analogy with a servo-mechanical system, the feed-back part of which is restrained.