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William H. Calvin
University of Washington
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Electroencephalography and Clinical Neurophysiology 34:337-351 (1973)

copyright ©1973 by authors and publisher

Calvin, W. H., Ojemann, G. A., and Ward, A. A., Jr. (1973). Human cortical neurons in epileptogenic foci: Comparison of inter-ictal firing patterns to those of "epileptic" neurons in animals. Electroencephalography and Clinical Neurophysiology 34:337-351.

SUMMARY

1. Extracellular recordings of the spontaneous firing patterns of cortical neurons were obtained in patients undergoing craniotomy for the surgical excision of an epileptogenic focus.

2. Because many kinds of experimental "epileptic" foci in animals exhibit cells with high frequency (200 500/sec) bursts of action potentials, lasting 5-50 msec and recurring many times per second, we explored the electrocorticographically defined epileptogenic focus in humans in search of bursting firing patterns.

3. In addition to normal firing patterns, many cells near the focus exhibited "epileptic" bursting firing patterns. Sometimes, normal and bursting cells could be recorded simultaneously, indicating that cells in proximity to one another are not uniform in such firing properties.

4. Such high frequency bursts are not typically the result of artifact such as micro-electrode pressure upon a cell, or heartbeat or respiratory movements of the cortex. Most bursting cells were obtained under operating conditions invalving local anesthesia, but similar results were seen under general anesthesia.

5. Bursts were not necessarily synchronized with the LEG sharp waves, nor with bursts from other simultaneously recorded neurons.

6. Attempts were matte to modify the burst patterns by arousing a sleeping patient and by electrical stimulation of the adjacent cortical surface. While some modifications in the rate of recurrence of the bursts could be obtained, the timing patterns of the first few spikes within a burst did not change readily.

7. High frequency tonic firing was also seen. Some such activity could be observed to undergo spontaneous changes from silence to high frequency tonic firing and then to bursts.

8. Within a burst, the timing of spikes may be very repeatable (stereotyped bursts) in some cases. In a few cases, the structured bursts reported in chronic monkey foci have been observed, where there seems to be a characteristic pause in the firing after the first one or two spikes and then a resumption of high frequency firing in a manner identical to the stereotyped bursts. These structured timing patterns have been considered a clue towards the identification of primarily dysfunctional epileptic neurons (in contrast to normal cells recruited into bursting firing patterns by an abnormally large synaptic input).

9. We would conclude that there is a good correspondence between the chronic alumina "epileptic" foci in animals and the human disease, insofar as the inter-ictal firing patterns of neurons near the focus is concerned.


RealAudio file allows you
to listen to a sample of the audio monitor,
amplifying the signal of several cortical neurons
near the epileptic focus in an awake patient
prior to removal of the epileptic region of brain.


RESUME

NEURONES CORTICAUX DES FOYERS EPILEPTOGENES CHEZ L HOMME: COMPARAISON DES PATTERNS DE DBCHARGES INTER-ICTAUX A CEUX DES NEURONES "EPILEPTIQUES CHEZ L ANIMAL

1. L'enregistrement extra-cellulaire des patterns de decharge spontanes des neurones corticaux a ete obtenu chez des malades chez qui une craniotomie etait effectuee pour excision chirurgicale d'un foyer epileptogene.

2. Du fait que plusieurs sortes de foyers "epileptiques" experimentaux chez ['animal montrent des cellules avec des bouffees de haute frequence (200 a 500/sec) de potentials d'action, durant 5 a 50 msec et se repetant plusieurs fois par seconde, nous avons explore le foyer epileptogene defini du point de vue electrocorticographique chez l'homme a la recherche de ces patterns de decharge en bouffees.

3. En plus des patterns normaux de decharge, plusieurs cellules proches du foyer ont montre des patterns de decharge "epileptiques" en bouffees. Parfois, les cellules normales et les cellules dechargeant en bouffees pouvaient etre enregistrees simultanement, indiquant que des cellules proches l'une de l'autre n'ont pas les memes proprietes de decharge.

4. Ces bouffees de haute frequence ne vent pas typiquement le resultat d'artefacts tels que pression de la micro -electrode sur une c ell u le. ou retentissement des battements cardiaques ou des mouvements respiratoires sur le cortex. La plupart des cellules qui dechargent en bouffees ont ete obtenues dans des conditions operatoires impliquant l'anesthesie locale, mais des resultats semblables ont ete observes sous anesthesia generale.

5. Les bouffees ne vent pas necessairement synchrones des ondes pointues de 1'EEG ni des bouffees venant d'autres neurones enregistres simultanement.

6. On a essaye de modifier les patterns de decharge en bouffees en eveillant un malade en train de dormir ou par stimulation electrique de la surface corticale adjacente. Bien que quelques modifications de la frequence de survenue des bouffees poissent etre obtenues, les patterns temporels des toutes premieres pointes a l'interieur d'une bouffee ne varient pas volontiers.

7. Des decharges toniques de frequence elevee ont ete egalement observees. Certaines activites de ce type peuvent presenter des modifications spontanees allant du silence a une decharge tonique de haute frequence, puis aux bouffees.

8. A l'interieur d'une bouffee, l'organisation temporelle des pointes peut, dans certains cas, se repeter (bouffees stereotypees). Dans quelques cas, les bouffees structurees qui ont ete decrites dans les foyers chroniques du singe ont ete observees, avec pause caracteristique a l'interieur de la decharge, apres la premiere ou les deux premieres pointes, puis resurgence d'une decharge de haute frequence d'une maniere identique a celle des bouffees stereotypees. Ces patterns structures dans le temps ont ete consideres comme un moyen d'identifier les neurones epileptiques primairement atteints (par opposition aux cellules normales recrutees dans les patterns de decharge en bouffees par une afference synaptique anormalement importante).


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