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Cognitive manipulation of laser pain-evoked potentials
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Society Proceedings
19. Cognitive manipulation of laser pain-evoked potentials. -
R.
Zaslansky, E. Sprecher and D. Yarnitsky (Institute of Clinical Neurophysiology, Rambam Medical Center and Technion Medical School, Haifa) The laser evoked potential (LEP) is characterised by a negative peak at * 240 msec and a positive peak at 3.50-400 msec after stimulation. Competing interpretations are that: (1) the LEP measures the sensory aspects of pain; (2) although components relating to painfulness of the stimulus exist, because the topography, latency and stimulus characteristics of LEPs resemble P300 “odd-hall” potentials, the LEP includes components relating to cognitive processing of pain. To assess these interpretations we tested whether LEPs can be manipulated by cognitive factors which included the degree of attention paid to the stimulus (experiment 1, n = 9) and odd-bal1 and task P300 stimulus presentations (experiment 2, n = 10). A CO, laser was used for stimulation of the dorsal aspect of the hand. The wave forms in experiment 1 exhibit characteristic LEP peaks. Multivariate analysis of peak parameters employed 2-factor repeated measures ANOVAs (Task and Site). Both factors significantly influenced the P amplitude. In experiment 2, LEP topography is consistent with previous LEP and P300 studies. Three-factor repeated measures (Task, Frequency and Site) ANOVAs on peak parameters yielded a significant effect for Frequency and Site for P amplitude. Thus, components in the LEP can be affected by cognitive factors of the P300 family. Further studies should separate cognitive from pain components in this potential. 20. Dynamic and static posturography in a group of dyslectic adoles-
cents. - Y. Mor, 2. Dvir and N. Gadoth (Department of Neurology, Beilinson Medical Center, Petah Tiqva, and Section of Physiotherapy, SacWer Faculty of Medicine, Tel Aviv University, Tel Aviv)
It is wel1 documented that in a large number of adolescents with dyslexia, one of the frequent “soft signs” is motor clumsiness. Two groups of dyslectic and non-dyslectic Israeli boys matched for age and IQ underwent dynamic and static posturography. Al1 participants had above average IQ and were otherwise healthy. Language, arithmetic calculation, visuomotor perception and fine and gross motor coordination were scored according to Paine and Oppe. A self-assessment and self-appreciation questionnaire was completed by each subject. Posturography disclosed a significant impairment of sensory axial balance in the dyslectic group only in static balance tests. Severity of the balance impairment was unrelated to the degree of dyslexia. 21. Effects of uncertainty on switching abilities in Parkinson’s dis-
ease (PD). - R Inzelberg qb, M. Plotnik b, E. Schechtman ‘, T. Flash b and A.D. Korczyn ’ (’ Dept. of Neurology, Tel Aviv Medical Center, Tel Aviv, b Dept. of Applied Mathematics and Computer Science, Weizmann Institute of Science, Rehovot, and ’ Computer Center, Weizmann Institute of Science, Rehovot) We analyzed the switching abilities of PD patients in a reaching task of the upper limb using the double-step target displacement paradigm. The effect of uncertainty was examined using a single target displacement to a fixed location, instead of the multiple possible locations which are usually used in this paradigm. PD patients and age-matched controls were seated in front of a digitizing table. They were presented with a visual target which could remain lit throughout the entire trial or could be unexpectedly displaced to another location. There always was a tempora1 uncertainty with regard to the time of target displacement, with interstimulus intervals (ISI) ranging between 50 and 350 msec. Both groups reacted to the target displacement (RT,) much slower than to the first
target (RT,) (P < 0.01). When the single target configuration was used, the initial direction of the movement varied as a function of the modification time between the appearance of the first target and target displacement (RT,-ISI). This occurred in both groups, but to a lesser extent in PD patients. In the multiple target displacement situation, PD patients showed no correlation between the initial movement direction and the modification time (P < 0.01). Our results suggest that elderly controls and PD patients are unable to process 2 stimuli in a parallel way. These findings indicate that while PD patients can use predictive spatial information, the inability to modify the initial movement direction is accentuated when spatial uncertainty exists. Thus, abnormalities in motor switching abilities in PD patients extend beyond tempora1 delays in motor preparation.
22. The effects of abrupt changes in PaCO, on the cerebral circulation and on the electroencephalogram in normal volunteers. - J. Sade, M. Neufeld ‘, N. Bornstein ‘, E. Nechushtan ‘, A. Zilbiger, P. Sorkine and P. Halpern (Departments of Anesthesia and ’ Neurology, Tel Aviv Medical Center, Ichilov Hospital, Tel Aviv) The cerebrovascular and EEG changes occurring during an abrupt decrease from high PaC02 were investigated. Subjects were 6 consenting young adults. Hypercapnia was induced by rebreathing. Subjects were then switched to oxygen or room air. Transcranial Doppler sonography, middle cerebral artery blood flow velocity (VMCA) and brain electrical activity mapping (BEAM) in the posterior head regions were carried out. When peak ETCO, was 8.3 f 0.7%, V,,, increased by 77.7% above baseline (55.8 f 11.8 to 97.4 f 17.5 cm/sec). V,,, decreased to baseline within 40.6 f 9.9 sec, dropping to 70.2 f 11.0% below baseline after 140.7 + 66 sec. During hypercarbia there was a significant decrease in alpha and increase in delta EEG activities compared to baseline. When deV MCA dropped to the nadir, alpha activity remained significantly creased. The present study shows, for the first time, the changes occurring in V,,, and EEG when PaCO, decreases suddenly from hypercarbia. EEG changes can perhaps be explained by anesthetic effects of COz rather Upon discontinuation of CO, exposure, VhlCA than changes in V,,,. decreased rapidly and dramatically to below baseline. Assuming that the geometry of the MCA does not change significantly, this reflects changes in cerebral blood flow. We need to reassess the safety of acutely hyperventilating patients with hypercarbic ventilatory failure.
23. Mutual interaction among sensory cells in dorsal root ganglia. R. Amir and M. Devor (Department of Cell and Animal Biology, Life Sciences Institute, Hebrew University, Jerusalem)
When spike activity is evoked in primary afferent neurons in rat dorsal root ganglia (DRGs) in vivo it excites repetitive firing in many passive neighboring neurons sharing the same DRG. Since this cross-excitation phenomenon recruits neurons in addition to the ones that stimulated directly, it might be expected to trigger paraesthesias and pain. This, of course, does not happen under normal conditions although it may in the case of neuropathy. In this study we ask why cross-excitation is not expressed in healthy individuals. Intracellular recordings were made from neurons in excised rat L4 and L.5 DRGs. Stimuli were delivered either to the impaled cel1 directly through the recording micropipette Cl-200 Hz), to the axons of neighboring cells (“conditioning tetani,” 10 S, 50 and 100 Hz), or to the neighbors and recorded cel1 axons simultaneously. We found that conditioning tetani depolarized _ 90% of the impaled neurons and also increased their spikíng activity. These effects probably underly cross-excitation seen in vivo. In contrast, direct stimulation of each of the recorded neurons evoked a hyperpolarizing shift accompanied by suppressed excitability. We then combined direct stimulation with stimulation of the neighbors by stimulating the whole nerve. This evoked cross-excitation and suppression simultaneously. The net result was sup-
Society Proceedings
19. Cognitive manipulation of laser pain-evoked potentials. -
R.
Zaslansky, E. Sprecher and D. Yarnitsky (Institute of Clinical Neurophysiology, Rambam Medical Center and Technion Medical School, Haifa) The laser evoked potential (LEP) is characterised by a negative peak at * 240 msec and a positive peak at 3.50-400 msec after stimulation. Competing interpretations are that: (1) the LEP measures the sensory aspects of pain; (2) although components relating to painfulness of the stimulus exist, because the topography, latency and stimulus characteristics of LEPs resemble P300 “odd-hall” potentials, the LEP includes components relating to cognitive processing of pain. To assess these interpretations we tested whether LEPs can be manipulated by cognitive factors which included the degree of attention paid to the stimulus (experiment 1, n = 9) and odd-bal1 and task P300 stimulus presentations (experiment 2, n = 10). A CO, laser was used for stimulation of the dorsal aspect of the hand. The wave forms in experiment 1 exhibit characteristic LEP peaks. Multivariate analysis of peak parameters employed 2-factor repeated measures ANOVAs (Task and Site). Both factors significantly influenced the P amplitude. In experiment 2, LEP topography is consistent with previous LEP and P300 studies. Three-factor repeated measures (Task, Frequency and Site) ANOVAs on peak parameters yielded a significant effect for Frequency and Site for P amplitude. Thus, components in the LEP can be affected by cognitive factors of the P300 family. Further studies should separate cognitive from pain components in this potential. 20. Dynamic and static posturography in a group of dyslectic adoles-
cents. - Y. Mor, 2. Dvir and N. Gadoth (Department of Neurology, Beilinson Medical Center, Petah Tiqva, and Section of Physiotherapy, SacWer Faculty of Medicine, Tel Aviv University, Tel Aviv)
It is wel1 documented that in a large number of adolescents with dyslexia, one of the frequent “soft signs” is motor clumsiness. Two groups of dyslectic and non-dyslectic Israeli boys matched for age and IQ underwent dynamic and static posturography. Al1 participants had above average IQ and were otherwise healthy. Language, arithmetic calculation, visuomotor perception and fine and gross motor coordination were scored according to Paine and Oppe. A self-assessment and self-appreciation questionnaire was completed by each subject. Posturography disclosed a significant impairment of sensory axial balance in the dyslectic group only in static balance tests. Severity of the balance impairment was unrelated to the degree of dyslexia. 21. Effects of uncertainty on switching abilities in Parkinson’s dis-
ease (PD). - R Inzelberg qb, M. Plotnik b, E. Schechtman ‘, T. Flash b and A.D. Korczyn ’ (’ Dept. of Neurology, Tel Aviv Medical Center, Tel Aviv, b Dept. of Applied Mathematics and Computer Science, Weizmann Institute of Science, Rehovot, and ’ Computer Center, Weizmann Institute of Science, Rehovot) We analyzed the switching abilities of PD patients in a reaching task of the upper limb using the double-step target displacement paradigm. The effect of uncertainty was examined using a single target displacement to a fixed location, instead of the multiple possible locations which are usually used in this paradigm. PD patients and age-matched controls were seated in front of a digitizing table. They were presented with a visual target which could remain lit throughout the entire trial or could be unexpectedly displaced to another location. There always was a tempora1 uncertainty with regard to the time of target displacement, with interstimulus intervals (ISI) ranging between 50 and 350 msec. Both groups reacted to the target displacement (RT,) much slower than to the first
target (RT,) (P < 0.01). When the single target configuration was used, the initial direction of the movement varied as a function of the modification time between the appearance of the first target and target displacement (RT,-ISI). This occurred in both groups, but to a lesser extent in PD patients. In the multiple target displacement situation, PD patients showed no correlation between the initial movement direction and the modification time (P < 0.01). Our results suggest that elderly controls and PD patients are unable to process 2 stimuli in a parallel way. These findings indicate that while PD patients can use predictive spatial information, the inability to modify the initial movement direction is accentuated when spatial uncertainty exists. Thus, abnormalities in motor switching abilities in PD patients extend beyond tempora1 delays in motor preparation.
22. The effects of abrupt changes in PaCO, on the cerebral circulation and on the electroencephalogram in normal volunteers. - J. Sade, M. Neufeld ‘, N. Bornstein ‘, E. Nechushtan ‘, A. Zilbiger, P. Sorkine and P. Halpern (Departments of Anesthesia and ’ Neurology, Tel Aviv Medical Center, Ichilov Hospital, Tel Aviv) The cerebrovascular and EEG changes occurring during an abrupt decrease from high PaC02 were investigated. Subjects were 6 consenting young adults. Hypercapnia was induced by rebreathing. Subjects were then switched to oxygen or room air. Transcranial Doppler sonography, middle cerebral artery blood flow velocity (VMCA) and brain electrical activity mapping (BEAM) in the posterior head regions were carried out. When peak ETCO, was 8.3 f 0.7%, V,,, increased by 77.7% above baseline (55.8 f 11.8 to 97.4 f 17.5 cm/sec). V,,, decreased to baseline within 40.6 f 9.9 sec, dropping to 70.2 f 11.0% below baseline after 140.7 + 66 sec. During hypercarbia there was a significant decrease in alpha and increase in delta EEG activities compared to baseline. When deV MCA dropped to the nadir, alpha activity remained significantly creased. The present study shows, for the first time, the changes occurring in V,,, and EEG when PaCO, decreases suddenly from hypercarbia. EEG changes can perhaps be explained by anesthetic effects of COz rather Upon discontinuation of CO, exposure, VhlCA than changes in V,,,. decreased rapidly and dramatically to below baseline. Assuming that the geometry of the MCA does not change significantly, this reflects changes in cerebral blood flow. We need to reassess the safety of acutely hyperventilating patients with hypercarbic ventilatory failure.
23. Mutual interaction among sensory cells in dorsal root ganglia. R. Amir and M. Devor (Department of Cell and Animal Biology, Life Sciences Institute, Hebrew University, Jerusalem)
When spike activity is evoked in primary afferent neurons in rat dorsal root ganglia (DRGs) in vivo it excites repetitive firing in many passive neighboring neurons sharing the same DRG. Since this cross-excitation phenomenon recruits neurons in addition to the ones that stimulated directly, it might be expected to trigger paraesthesias and pain. This, of course, does not happen under normal conditions although it may in the case of neuropathy. In this study we ask why cross-excitation is not expressed in healthy individuals. Intracellular recordings were made from neurons in excised rat L4 and L.5 DRGs. Stimuli were delivered either to the impaled cel1 directly through the recording micropipette Cl-200 Hz), to the axons of neighboring cells (“conditioning tetani,” 10 S, 50 and 100 Hz), or to the neighbors and recorded cel1 axons simultaneously. We found that conditioning tetani depolarized _ 90% of the impaled neurons and also increased their spikíng activity. These effects probably underly cross-excitation seen in vivo. In contrast, direct stimulation of each of the recorded neurons evoked a hyperpolarizing shift accompanied by suppressed excitability. We then combined direct stimulation with stimulation of the neighbors by stimulating the whole nerve. This evoked cross-excitation and suppression simultaneously. The net result was sup-