Bipolar Derivations Research Articles

Functional topography of the human mu rhythm

Abstract Topographic and functional testing was conducted to determine if the Rolandic mu rhythm (rhytme en arceau) could be reliably detected from the human scalp, and to describe its spatiotemporal and functional characteristics in relation to the feline sensorimotor rhythm (SMR) and the human occipital alpha rhythm. Mu activity was rarely visualized clearly in referential recordings or from the major 10–20 system locations, but was detected by power spectral analysis and functional testing in 7 of 14 subjects studied. It was best recorded in closely spaced bipolar derivations from central areas posterior to the central sulcus as shown in topographic analysis of its occurrence at rest and its reactivity to contralateral hand movement. Mu activity was attenuated by voluntary movement and somatosensory stimulation but was minimally affected by visual stimulation. Its frequency ranged within the alpha band (mean of 10.1 c/sec), but was separate from the occipital alpha rhythm and stable in frequency across days. The anatomical and functional similarities between human mu activity and the feline SMR suggested that they are functionally analogous resting rhythms which are disrupted primarily by input to the somatosensory system. The concept of sensory-specific alpha rhythms was discussed, in which the mu rhythm was conceptualized as a central “somatosensory alpha rhythm” in contrast to the occipital “visual alpha rhythm”.

Spatio-temporal organization of EEG in premature infants and full-term new-borns

Inter- and intrahemispheric EEG relationships were studied as a function of maturation in new-born infants. The spatio-temporal organization of EEG activity obtained during the two stages of sleep described in new-born infants - quiet sleep and active sleep - was analysed in 9 full-term new-born infants and 5 prematures (6 records). EEGs were recorded through transverse parietal montage made up of six bipolar derivations. Two epochs of 1.5 min each - successively obtained in both stages of sleep - were digitized, filtered in three frequency bands (beta, theta and delta) and computer-processed according to two methods, factor analysis and rhythms averaging. 1. The following EEG characteristics were found in both groups: (a) Instability of frequency within each frequency band (beta, theta and delta). However, theta activity was the most stable of the three, especially in quiet sleep. (b) Variability of topographical organization (i.e., localization of maxima of potentials) from one moment to another in both stages of sleep and in the three frequency bands. In spite of this intra-individual variability some sort of "average structure" was found in all infants; it was characterized by usually lateral and often symmetrical positions of the maxima of potential on the two hemispheres. For the same infant this structure was the same in the three frequency bands. (c) Poor interhemispheric relationships under all conditions, as well as poor interregional links in one hemisphere. 2. Some EEG characteristics differentiated the two groups and thus seemed to be related to maturation. Compared to full-term newborns the premature group showed: better stability for all three activities, especially for beta activity; higher frequency and larger amplitude of beta activity; better inter- and intrahemispheric relationships; fewer differences related to sleep stages. These results are discussed in terms of organization of the underlying cortical generators. The authors suggest that the active areas would increase in number and in surface with maturation, whereas the links between these different separate areas would remain very poor in the human full-term new-borns as well on one hemisphere as across hemispheres. This last finding would argue against the hypothesis that the corpus callosum which, as is well known, matures early, plays an important role in the establishment of interhemispheric links.

An on-line transformation of EEG scalp potentials into orthogonal source derivations

A new type of EEG derivation has been investigated. This derivation, constituting a practical implementation of the Laplace operator, detects source activity as it appears at the surface level of the scalp. It is realized in the 10-20 system of electrode placement basically as an analogue superposition of four bipolar derivations, forming a star-like configuration around each electrode. Visual estimation of the topographical origins of a pattern, is thus replaced by a more efficient on-line process, which derives the source activity at the position of each individual electrode. Practical correlation tests have shown that the separation of adjacent derivations is improved by a factor of between two and four, compared to the corresponding bipolar and common reference derivations. Any feature of local origin will therefore have a correspondingly increased signal-to-noise ratio prior to the stage of visual or automatic interpretation. As a consequence of the partition of the scalp field into 19 source zreas, instead of utilizing an arbitrary number of potential differences, one fixed montage with 19 recorder channels is sufficient to present the total surface activity, within the limits of resolution of the electrode system.

Symmetry of the visual evoked potential in normal subjects

Abstract Homologous pairs of VEPs from the 139 normal subjects were subjected to four different measures of symmetry, using central, occipital and temporal monopolar, and centro-occipital and occipito-temporal bipolar derivations. The general characteristics of the VEP sample were comparable with those described by other authors. Peak latency differences were very small irrespective of derivation, analysis interval of the VEP or measure of peak latency, being less than 5 msec for 85% of the population. Only 5% of VEP peaks appeared on one side exclusively, except during the interval between 0 and 62.5 msec, in which 12% of all peaks appeared only in one side. For the great majority of subjects, amplitude differences were not greater than 40%. Cross-correlation values were very high (80%

Potentiels evoques par l'apparition de patterns: effets de la dimension du pattern et de la densite des contrastes

This work has been performed to elicit the neurophysiological significance of each component of the visual evoked cortical response to checkerboard patterns. The variations in amplitude, polarity and chronotopographic organization of each component of the response have been studied for 8 normal subjects as a function of: checkerboard size (20°, 10°, 5°, 2°30′, 1°20′) and square size (40′, 20′, 10′, 5′). The stimulation was always binocular, the gaze being fixed in the centre of the checkerboard. After analogue-digital conversion averages were made, for each experimental situation, on 65 responses to stimuli given every 1540 msec and lasting 770 msec each. A topographic study was made with chains of bipolar derivations in 2 montages (longitudinal vertex-inion, transverse crossing the midline 2 cm above the inion). The results can be summarized as follows: The response to a 20° checkerboard made of 40′ squares (which serves as “reference response”, being obtained from 24 normal subjects) is made of 4 components: wave 0 (sink peaking at 60 msec), wave 1 (source peaking at 90 msec), wave 2 (sink peaking at 120 msec), wave 3 (long lasting source peaking towards 200 msec). Waves 0, 1 and 2 show phase reversal of gradients (maximum of potential) near the inion; wave 3 has its maximum in the parietal region. The response to a plain field of the same dimension (and of luminance twice as high as that of the checkerboard), is characterized by waves of much smaller amplitude and usually opposite polarity (in particular wave 0 is absent in plain field responses and wave 2 is either absent or replaced by a positive potential). As the checkerboard gets smaller (from 20° to 1°20′) the amplitude of each component gets smaller and the topographic organization of waves 1 and 2 changes, the maximum of potential getting more and more posterior (longitudinal montage) and lateral (transverse montage); the topography of wave 3 (longitudinal) does not change. When the square size changes (from 40′ to 5′), the chronotopographic organization of the response does not change. The amplitude of waves 0,1 and especially wave 2 does change: whatever the checkerboard size, wave 2 (sink peaking around 120 msec) is the largest with 20′ squares and the smallest with 5′ squares (for some subjects wave 2 entirely disappears in the latter case). The part played in this pattern response by the central and peripheral retina and the role of the density of contrasts, which might be related to the size of receptive fields, are discussed.

Reponses aux stimulations visuelles dans les etats de coma aigu et de coma chronique

Resume Les potentiels evoques par la lumiere (PEV) recueillis au niveau de la ligne mediane en derivations bipolaires (fronto-vertex et vertex-occiput) ont ete integres dans un Mnemotron CAT 400 C, chez des malades en etat de “coma depasse”, de coma aigu profond et en etat de coma chronique (41 sujets au total), au cours d'explorations electroencephalographiques. Ces etudes comportaient des sequences de 40 eclairs, repetees toutes les 5 min pendant 1 a 1,5 h chez un meme patient. 1. 1. Dans le “coma depasse” (stade IV de Fischgold et Mathis), la seule reponse integrable est un electroretinogramme (ERG). 2. 2. Dans les comas aigus (stade III de Fischgold et Mathis), d'evolution fatale a breve echeance, on note: (a) la stereotypie et l'areactivite des reponses occipitales au cours d'un meme examen; (b) la deterioration plus precoce du PEV cortical que celle des activites spontanees et, dans la phase terminale, son extinction precedant toujours celle de l'EEG; (c) une contamination des derivations cerebrales par l'ERG augmentant nettement lors de l'aggravation electroclinique. 3. 3. Dans les comas ayant evolue vers la chronicite: (a) les PEV, extremement amortis dans les stades initiaux, peuvent montrer une recuperation ulterieure pour se fixer ensuite, au cours d'une troisieme periode, en des aspects peu evolutifs, eux-aussi stereotypes; (b) au cours de cette troisieme periode, une differenciation veille-sommeil des reponses evoquees par la lumiere s'etablit de plus en plus nettement: yeux ouverts, PEV et ERG sont soit inexistants, soit considerablement attenues, contrastant avec un reflexe photo-palpebral exagere. Pendant le sommeil, abolition du reflexe photo-palpebral, majoration de l'ERG, facilitation du PEV avec possibilite d'elaboration d'une postp-decharge rythmique; (c) la stereotypie des PEV est donc maintenue dans le coma chronique, mais avec deux modalites d'expression: l'une propre a l'etat de veille, l'autre observee pendant le sommeil. Cette differenciation veille-sommeil est l'une des caracteristiques du passage a la chronicite; (d) il existe une concordance globale entre aspects de l'EEG spontane et responses corticales evoquees mais des discordances apparaissent lorsque les divers elements sont examines dans leur detail.

Relationship between EEG, personality and vigilance

Abstract The dependence of alpha frequencies upon vigilance performance and upon the personality variables of rigidity, extraversion and neurotic tendency was investigated. The EEG was recorded from bipolar derivations F3-C3, P3-O1 and T5-O1 during various resting and task periods. The independent evaluation of records from the latter two positions and the correlation of these with other data gave the following results: 1. 1. Good vigilance correlates positively with low (8–9 c/sec) and negatively with high (12–13 c/sec) alpha frequencies during both task performance and the subsequent resting stage. 2. 2. Good vigilance correlates negatively with the alpha index in the subsequent resting period. 3. 3. Rigidity correlates positively with the error score in the vigilance task and negatively with the percentage of correct responses. 4. 4. Rigidity correlates negatively with low 5. (8–9 c/sec) and positively with high (12–13 c/sec) alpha frequencies. 6. 5. Neurotic tendency correlates positively with intermediate (19-11 c/sec) alpha frequencies during the vigilance task and with the alpha index during and after this task. 7. 6. Neurotic tendency, however, correlates negatively with the intermediate (10–11 c/sec) alpha frequencies during the resting period prior to the task. 8. 7. Poor performance (error score) on the arithmetic tasks correlates negatively with the alpha index during the resting stages. 9. 8. Poor performance (error score) on the arithmetic tasks correlates positively with the low (8–9 c/sec) alpha frequencies during the vigilance task. The results suggest that good vigilance is associated with the lower alpha frequencies and poor vigilance with the higher ones. Rigidity appears to be associated with high alpha frequencies and poor performance. When neurotic tendency is high, performance of the vigilance task causes an increase rather than a decrease in 10–11 c/sec waves.

Neural limitations of visual excitability VIII: Binocular convergence in cat geniculate and cortex

Excitability cycles for the lateral geniculate body and the visual cortex were obtained in 49 locally anesthetized-immobilized cats, by plotting the response changes to a test Mash (Ft) against the time interval from a supraliminal conditioning flash (Fc), presented either to the same (monocular stimulation) or to the contralateral (interocular stimulation) eye. For both forms of stimulation, the conditioning flash response disrupted the test flash response, either in amplitude or duration, depending upon the temporal interval. With monocular stimulation, increasing either Fc duration or luminance prolonged the recovery cycle at both cortex and LG. With interocular stimulation, however, cortical recovery was more rapid, and only slightly affected by Fc parameters. Interocular interaction could not be demonstrated at LG with closely spaced bipolar derivations. These findings suggest that both peripheral and central processes limit visual excitability, cortical rather than geniculate mechanisms being more significant in the latter instance. On obtient sur 49 chats immobilisés par anesthésie locale les cycles d'excitabilitédu corps genotiillélatéral et du cortex visuel, en mesurant les changements de réponseàunéclair (Ft) en fonction de l'intervalle de tempsécoulédepuis unéclair supraliminal de conditionnement (Fc), présentésoit dans le meˆme œil (stimulation monoculaire) soit dans l'autre (stimulation interoculaire). Dans les deux cas, la réponseà Fc réduit celleà Ft, soit en amplitude soit en durée, et cet effet dépend de l'intervalle de temps entre leséclairs. En stimulation monoculaire, l'accroissement de Fc en durée ou en luminance augmente le temps de récupérationàla fois dans le cortex et le corps genouillé. En stimulation interoculaire, la récupération corticale est plus rapide et dépend peu des paramétres de Fc. On n'a pas pu démontrer l'interaction binoculaire dans le corps genouilléavec des dérivations bipolaires rapprochées. Ces résultats suggèrent que des processus périphériques et centraux limitentàla fois l'excitabilitévisuelle, le roˆle des mécanismes corticauxétant plus net que ceux du corps genouillédans ce dernier cas. Erregungszvklen für das corpus geniculatum laterale und den visuellen Cortex wurden an 49 lokal betäubten und gelähmten Katzen gemessen. Dazu wurden dieÄnderungen der Antwort auf einen Testblitz (Ft) gegen den zeitlichen Abstand zu einemüberschwelligen Adaptationsreiz (Fc) aufgetragen, der entweder dem gleichen (mono-kulare Reizung) oder dem kontralateralen Auge (interokulare Reizung) dargeboten wurde. Bei beiden Reizarten störte der Adaptationsblitz entweder die Dauer oder die Amplitude der Antwort des Testblitzes, je nach dem zeitlichen Abstand. Bei monokularer Reizung verlängert eine Vergrösserung der Leuchtdichte oder Dauer von Fc den Erholungszyklus sowohl im Cortex als auch im geniculatum laterale. Bei interocularer Reizung jedoch war die Erholung im Cortex schneller und nur wenig durch die Parameter von Fc beeinfiusst. Am geniculatum laterale konntex mit nahe beisammen liegenden bipolaren Ableitelektroden keine interokulare Wechselwirkung gezeigt werden. Diese Ergebnisse weisen daraufhin, dass sowohl zentrale als auch periphere Prozesse die visuelle Erregung begrenzen. Bei letzteren sind die Vorgänge im Cortex bedeutender als die im geniculatum. Были oпpeдeлeны циклы вoзбyдимocти для лaтepaльных кoлeнхaтых тeл и зpитeльнoй кopы y 49 мecтнo aнacтeзиpoвaнных и иммoбилизoвaнных кoшeк пyтeм peгиcтpaции измeнeния peaкций нa тecтoвyю вcпышкy cвeтa (Ft) в зaвиcимocти oт интepвaлa вpeмeни oт cвepхпopoгoвoй ocнoвнoй вcпышки (Fc), дaвaeмoй либo в тoт жe глaз (мoнoкyляpнaя cтимyляция), либo жe нa дpyгoй глaз (бинoкyляpнaя cтимyляция). Пpи oбeих фopмaх cтмyляции, peaкция нa ocнoвнyю вcпышкy нapyшaлa peaкцию нa тecтoвyю вcпышкy, влияя либo нa ee aмплитyдy, либo нa ee длитeльнocть, в зaвиcимocти oт вpeмeннoгo интepвaлa. Пpи мoнoкyляpнoй cтимyляции yвeлихeниe длитeльнocти Fc или жe ee яpкocти yдлинялo вoccтaнoвитeльный цикл и в кope и в лaтepaльнoм кoлeнхaтoм тeлe. Пpи интepoкyляpнoй cтимyляции, oднaкo, кopтикaльнoe вoccтaнoвлeниe былo бoлee быcтpым и тoлькo нeмнoгo зaвиcит oт пapaмeтpoв (Fc). Интepoкyляpнoe взaимoдeйcтвиe нe былo oбнapyжeнo в лaтepaльнoм кoлeнхaтoм тeлe пpи бипoляpнoм oтвeдeнии c близкo pacпoлoжeнными элeктpoдaми. Эти peзyльтaты пoкaзывaют, хтo кaк пepифepихecкиe, тaк и цeнтpaльныe пpoцeccы влияют нa зpитeльнyю вoзбyдимocть, пpи хeм в этoм oтнoшeнии мeхaнизмы кopтикaльныe имeют бoльшee знaхeниe, хeм мeхaнизмы кoлeнхaтых тeл.

Excitability cycle of the visual cortex in normal subjects during psychosensory rest and cardiazolic activation

The recovery cycle of the human visual cortex in conditions of psychosensory rest and after i.v. administration of 250 and 500 mg of Cardiazol was studied in 10 normal subjects by means of the evoked photic potential. The evoked cortical responses were recorded from the scalp in bipolar derivation obtained by means of a CAT 400 B Mnemotron. Paired flashes were emitted at various intervals (20-30-40-50-70-80-100-120-150-170-200-230 msec). From the complex response obtained from the two flashes (R1 + R2), the response (R1) evoked by the first flash (conditioning flash) was subtracted, thus obtaining the response (R2) to the second flash (test flash). The ratio (R2/R1) between the amplitudes of waves III and VII of the two evoked responses so obtained was taken as the index of the state of cortical excitability in successive moments. Variations with respect to unity were then considered. If the ratio equals zero the cortex is not excitable further (R2 = 0), if less than one, excitability is reduced (R2 < R1), if greater than 1, it is increased (R2 > R1) and, finally, if it equals one, the cortex is in a condition of normal excitability (R2 = R1). The results obtained showed that the recovery cycle of the visual cortex in man in psychosensory res consists of: o (1) a period of absolute refractivity of 40 msec; (2) a period of supernormal facilitation lasting from 80 to 100 msec after stimulus with a maximum at 100 msec; (3) a period of subnormal excitability from 120 to 150 msec after the flash with a maximum at 150 msec; (4) the return to the state of normal excitability about 200 msec after the flash. I.v. administration of Cardiazol in doses of 250 and 500 mg provokes modifications in the evoked photic potential and in the cortical recovery cycle. The basal evoked response is increased in amplitude in its later components. The cortical recovery cycle has a shorter duration and is made up as follows: o (1) period of absolute refractivity 30 msec; (2) phase of supernormal excitability from 50 to 80 msec after the flash with a maximum at 80 msec; (3) phase of subnormal excitability between 100 and 120 msec with a maximum at 120 msec; (4) recovery of normal excitability at 150 msec after the stimulus. The described modifications are quite similar with 250 and 500 mg of i.v. Cardiazol. Both in basal conditions and during Cardiazol administration an increase in latencies and durations of waves III and VII of the evoked potential was noted in the period of maximum facilitation. Like supranormal excitability itself, it seems that these facts can be attributed to phenomena of spacial summation depending on the neuron contingent of the subliminal fringe excited by the second flash. In conclusion, the increase in cortical excitability produced by Cardiazol is pointed out. This also seems to predispose the cortex to respond to more frequent sensory stimuli by shortening the duration of the recovery cycle.

An Experimental Study of Monopolar and Bipolar Derivations in the Human Electroencephalogram.

ConclusionsIt has been shown that the important characteristic amplitude properties of the alpha component of the normal human EEG, in the usual monopolar and bipolar derivations primarily depend on the attenuating properties of the tissue through which the potential difference is transmitted. Moreover, noting the correspondence between waveforms seen in the normal EEG and those produced by an artificial occipital electric dipole in the cadaver, it is clear that the spread of an occipital electric disturbance is an excellent model for the production of the amplitude characteristics of the basic alpha component of the normal EEG.