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Lambda responses are related to functional asymmetry of the brain
245 5. Ivanov-Smolenskij (1949). Ocherki patophysiologii visshei nervnoj dejatelnosti. Moskva, “Medgiz”. 6. Pavlov, I.P. (1951). Polnoe sobranie sochinenij. Moskva, AN SSSR.
LAMBDA RESPONSES ARE RELATED TO FIJNCTIONAL ASYMMETRY OF THE BRAIN F. Jagla, V. Zikmund Institute of Normal and Pathological Physiology, Ctr. Physiol. Sci., Slovak Academy of Sciences, Bratislava, CSSR The external world is scanned, in foveate animals, by a sequence of the saccadic eye movements. Input of the visual information is accomplished between two consecutive saccades. In to the programming of each saccade enter: visual information from the preceding fixation, changes in visual, auditory and somesthetic inputs and internally generated cognitive demands as well. The central mechanisms that produce and integrate these contributions to saccade programming are largely unknown /Kurt&erg et al.,1980/. The programming of saccades and the processing of visual information in relation to saccadic eye movements can be approached in humans by studying the scalp recorded macropotentials timelocked to saccades. The averaged potentials timelocked to saccades and registered over the occipital areas are known as lambda responses. Lambda response takes on a complex configuration with a most constant and prominent feature being a deep positivity at about 160 ms after beginning of the saccade. Yagi /1979/reports increases in both amplitudes and latencies of some lambda response components with increasing of saccades in size. Some authors pointed to the changes in the amplitude and in the shape of the deep lambda positivity according to the characteristics of the visual background. The association of the lambda components with the onset and offset of saccades was the subject of Yagi’s study /1981/. The differences in those lambda components which precede the begin of the eye movements may be observed when the saccades are made either in a self-paced voluntary manner or in response is more prominent over the occipital areas with visually triggered saccades, the
slow motion preparatory component of an eye movement related potential is more prominent over the frontal eye fields with voluntary triggered saccades /Kurt&erg et al., 1980/. In one of our previous studies /Jagla et al., 198l/ we found that the saccades to the left in righthanders were more accurate than the saccades to the right. In lefthanders the reverse was true. The aim of this study has been to analyse the lambda responses from both the occipital regions with the saccadic eye movements to the left and to the right separately, when registered monopolarly. 20 healthy undergraduates, pronounced righthanders with normal vision, served as subjects. Ag/AgCl electrodes were affixed at 01 and 02 according to the 10-20 system. Linked mastoids served as reference. The EOG was recorded when electrodes at the outer canthi of the eyes were placed. The saccades were used as a trigger for the avemger ICA 70 4K. 50 sweeps were averaged for the saccades to the right and to the left respectively. Lambda responses were written out on an X-Y plotter. The saccadic eye movements were elicited by means of switching on and off the fiiational lamps. These visual targets were located in the centre of the panoramic screen and 100 to the right and loo to the left from the central lamp. The lamps were switched on and off at regular 2 seconds intervals alternatively. Subjects performed the saccades across a grid from the vertical black and white stripes /l:l ratio, width 5”/. The premotion positivity was found to begin 30 ms earlier /I73 ms/ with the saccadic eye movements to the right as compared to the left /143 ms/ above both the hemispheres with a slight prevalence of shorter latencies above the right hemisphere. the amplitude of the premotion positivity was, in general, more pronounced with the saccades to the right and it was 30% higher. The sharp Pl-Nl component which reflects the execution of a proper saccadic eye movement had the higher amplitude /1.43 p.V/ with the saccades to the right as compared to the left /1.18 pV, p c 0.05/. These amplitudes were found to be smaller above the right hemisphere but with the same right/left difference /1.38 pV : 1.11 pV, P < 0.05/. The peak of the P3 component has been mostly related to the maximal neuronal facilitation of the visual information processing at the new fKation. P3 latency was found to be shorter with the saccades to the
246 right as compared to the opposite side /left hemisphere - 7.3 p.V : 6.5 pV; right hemisphere - 7.8 pV : 6.3 pV, P < 0.051. These results suggest that there exist: /a/ a longer preparatory phase for saccadic eye movements to the right; /b/ a higher amplitude of the motion execution lambda component with saccades to the right; /c/ a longer latency of picking up new information after the saccades to the right and /d/ latencies generally shorter and amplitudes smaller of some lambda components over the right hemisphere. These results may point to the higher “readiness” to foveate the visual stimulus in the left half of the visual field in righthanders, which is in agreement with studies showing that the left half of the visual field has - in righthanders - the more important role in encoding the basic shape and space characteristics of visual stimuli, than the right half. References
Jagla, F. and Zilonund, V. I198 11 Saccadic eye movements and the cerebral hemisphere dominance. Cs. Oftal. 37: 132-137 Kurtzberg, D. and Vaughan, H.G. Jr. /1980/ Differential topography of human eye movement potentials preceding visually triggered and self - initiated sacades. In: Progress in Brain Research, Vol. 54, Komhuber et al./eds./, Elsevier, Amsterdam, pp. 203208 Yagi, A. 119791 Saccade size and lambda complex in man. Physiol. Psychol. 7: 370-376 Yagi, A. /1981/ Averaged cortical potentials /lambda responses/ time-locked to onset and offset of saccades. Physiol. Psychol. 9: 318-320
THE CHANGES IN EXCITABILITY OF SPINAL MOTONEURONS AT THE NOTION OF MOVEMENT J. Jagr 1st Department of Neurology, Bratislava, Czchoslovakia The basis for determination of the aim of our work was generally accepted theory that the voluntary movement is centrally planned (Humphrey, D.R., 1979). Higher-
order association areas together with “premotor” association areas transform a general “command” for movement into an appropriate pattern of excitation of somatotopically organized zones of the motor cortex. The question was whether the “imagined” plan of movement is reflected also at the spinal level, respectively at the lower ones. In other words we asked whether at the notion of movement also the irritability of spinal motoneurons is changed; criterion of this was the amplitude of the averaged F-wave. We stimulated n. medianus in the wrist by slightly increased threshold impulses and registered the F-waves at rest, at slight isometric contraction, and at the notion of it. Muscular responses were registered through the surface electrodes situated above m. opponens pollicis. We examined 16 healthy persons aged from 21 till 22 years in this way. It was found out that at the slight isometric cormaction the amplitude of averaged F-wave significantly increased (p 0.005). This finding is in agreement with the literary data (Upton, A.R.M. et al., 1979). Similar significant increase of F-wave may be observed at the notion of movement. There was no statistically significant difference between the amplitudes of F-wave at the slight isometric and at the “imagining” of it. Because imagination of movement increases the amplitude of the F-wave, it could be concluded that the plan of movement is transformed up to the spinal motoneurons. In the other group of 20 healthy volunteers of the above-mentioned age group, we compared the direct muscular responses (M-wave) at the above-mentioned stimulation of n. medianus. We found out that the amplitudes of response is not significantly changed neither at a weak innervation nor at the notion of movement. We can conclude that the cells of anterior spinal cords form the most peripheral nervous structure, the excitability of which change at the notion of movement. References
1. Humphrey, D.R. (1979). On the cortical of visually directed reacting: contribution by nonprecental motor ares. In: R.E. Talvot, D.R. Humphrey: Posture and movement edit. Raven Press, 1979; 51-52. 2. Upton, A.R.M., McComas, A.J. and Sicca, R.E.P. (1979). Potentiation of late responses evoked in muscle during effort. J. of Neurol. Neurosurg. and Psych., 1979; 699-711.
LAMBDA RESPONSES ARE RELATED TO FIJNCTIONAL ASYMMETRY OF THE BRAIN F. Jagla, V. Zikmund Institute of Normal and Pathological Physiology, Ctr. Physiol. Sci., Slovak Academy of Sciences, Bratislava, CSSR The external world is scanned, in foveate animals, by a sequence of the saccadic eye movements. Input of the visual information is accomplished between two consecutive saccades. In to the programming of each saccade enter: visual information from the preceding fixation, changes in visual, auditory and somesthetic inputs and internally generated cognitive demands as well. The central mechanisms that produce and integrate these contributions to saccade programming are largely unknown /Kurt&erg et al.,1980/. The programming of saccades and the processing of visual information in relation to saccadic eye movements can be approached in humans by studying the scalp recorded macropotentials timelocked to saccades. The averaged potentials timelocked to saccades and registered over the occipital areas are known as lambda responses. Lambda response takes on a complex configuration with a most constant and prominent feature being a deep positivity at about 160 ms after beginning of the saccade. Yagi /1979/reports increases in both amplitudes and latencies of some lambda response components with increasing of saccades in size. Some authors pointed to the changes in the amplitude and in the shape of the deep lambda positivity according to the characteristics of the visual background. The association of the lambda components with the onset and offset of saccades was the subject of Yagi’s study /1981/. The differences in those lambda components which precede the begin of the eye movements may be observed when the saccades are made either in a self-paced voluntary manner or in response is more prominent over the occipital areas with visually triggered saccades, the
slow motion preparatory component of an eye movement related potential is more prominent over the frontal eye fields with voluntary triggered saccades /Kurt&erg et al., 1980/. In one of our previous studies /Jagla et al., 198l/ we found that the saccades to the left in righthanders were more accurate than the saccades to the right. In lefthanders the reverse was true. The aim of this study has been to analyse the lambda responses from both the occipital regions with the saccadic eye movements to the left and to the right separately, when registered monopolarly. 20 healthy undergraduates, pronounced righthanders with normal vision, served as subjects. Ag/AgCl electrodes were affixed at 01 and 02 according to the 10-20 system. Linked mastoids served as reference. The EOG was recorded when electrodes at the outer canthi of the eyes were placed. The saccades were used as a trigger for the avemger ICA 70 4K. 50 sweeps were averaged for the saccades to the right and to the left respectively. Lambda responses were written out on an X-Y plotter. The saccadic eye movements were elicited by means of switching on and off the fiiational lamps. These visual targets were located in the centre of the panoramic screen and 100 to the right and loo to the left from the central lamp. The lamps were switched on and off at regular 2 seconds intervals alternatively. Subjects performed the saccades across a grid from the vertical black and white stripes /l:l ratio, width 5”/. The premotion positivity was found to begin 30 ms earlier /I73 ms/ with the saccadic eye movements to the right as compared to the left /143 ms/ above both the hemispheres with a slight prevalence of shorter latencies above the right hemisphere. the amplitude of the premotion positivity was, in general, more pronounced with the saccades to the right and it was 30% higher. The sharp Pl-Nl component which reflects the execution of a proper saccadic eye movement had the higher amplitude /1.43 p.V/ with the saccades to the right as compared to the left /1.18 pV, p c 0.05/. These amplitudes were found to be smaller above the right hemisphere but with the same right/left difference /1.38 pV : 1.11 pV, P < 0.05/. The peak of the P3 component has been mostly related to the maximal neuronal facilitation of the visual information processing at the new fKation. P3 latency was found to be shorter with the saccades to the
246 right as compared to the opposite side /left hemisphere - 7.3 p.V : 6.5 pV; right hemisphere - 7.8 pV : 6.3 pV, P < 0.051. These results suggest that there exist: /a/ a longer preparatory phase for saccadic eye movements to the right; /b/ a higher amplitude of the motion execution lambda component with saccades to the right; /c/ a longer latency of picking up new information after the saccades to the right and /d/ latencies generally shorter and amplitudes smaller of some lambda components over the right hemisphere. These results may point to the higher “readiness” to foveate the visual stimulus in the left half of the visual field in righthanders, which is in agreement with studies showing that the left half of the visual field has - in righthanders - the more important role in encoding the basic shape and space characteristics of visual stimuli, than the right half. References
Jagla, F. and Zilonund, V. I198 11 Saccadic eye movements and the cerebral hemisphere dominance. Cs. Oftal. 37: 132-137 Kurtzberg, D. and Vaughan, H.G. Jr. /1980/ Differential topography of human eye movement potentials preceding visually triggered and self - initiated sacades. In: Progress in Brain Research, Vol. 54, Komhuber et al./eds./, Elsevier, Amsterdam, pp. 203208 Yagi, A. 119791 Saccade size and lambda complex in man. Physiol. Psychol. 7: 370-376 Yagi, A. /1981/ Averaged cortical potentials /lambda responses/ time-locked to onset and offset of saccades. Physiol. Psychol. 9: 318-320
THE CHANGES IN EXCITABILITY OF SPINAL MOTONEURONS AT THE NOTION OF MOVEMENT J. Jagr 1st Department of Neurology, Bratislava, Czchoslovakia The basis for determination of the aim of our work was generally accepted theory that the voluntary movement is centrally planned (Humphrey, D.R., 1979). Higher-
order association areas together with “premotor” association areas transform a general “command” for movement into an appropriate pattern of excitation of somatotopically organized zones of the motor cortex. The question was whether the “imagined” plan of movement is reflected also at the spinal level, respectively at the lower ones. In other words we asked whether at the notion of movement also the irritability of spinal motoneurons is changed; criterion of this was the amplitude of the averaged F-wave. We stimulated n. medianus in the wrist by slightly increased threshold impulses and registered the F-waves at rest, at slight isometric contraction, and at the notion of it. Muscular responses were registered through the surface electrodes situated above m. opponens pollicis. We examined 16 healthy persons aged from 21 till 22 years in this way. It was found out that at the slight isometric cormaction the amplitude of averaged F-wave significantly increased (p 0.005). This finding is in agreement with the literary data (Upton, A.R.M. et al., 1979). Similar significant increase of F-wave may be observed at the notion of movement. There was no statistically significant difference between the amplitudes of F-wave at the slight isometric and at the “imagining” of it. Because imagination of movement increases the amplitude of the F-wave, it could be concluded that the plan of movement is transformed up to the spinal motoneurons. In the other group of 20 healthy volunteers of the above-mentioned age group, we compared the direct muscular responses (M-wave) at the above-mentioned stimulation of n. medianus. We found out that the amplitudes of response is not significantly changed neither at a weak innervation nor at the notion of movement. We can conclude that the cells of anterior spinal cords form the most peripheral nervous structure, the excitability of which change at the notion of movement. References
1. Humphrey, D.R. (1979). On the cortical of visually directed reacting: contribution by nonprecental motor ares. In: R.E. Talvot, D.R. Humphrey: Posture and movement edit. Raven Press, 1979; 51-52. 2. Upton, A.R.M., McComas, A.J. and Sicca, R.E.P. (1979). Potentiation of late responses evoked in muscle during effort. J. of Neurol. Neurosurg. and Psych., 1979; 699-711.