Comparaison de l'EEG recueilli sur le scalp avec l'activité élémentaire des dipoles corticaux radiaires

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1. 1. Cats and rabbits were used for both acute and chronic experiments during which a comparison was carried out between monopolar and transcortical EEG recordings, the latter being known to give reliable account of the activity of the area from which it is derived. The active electrode of the monopolar lead was placed near the transcortical bipolar electrode. 2. 2. Surface negative and surface positive spindles, slow waves appearing during spontaneous sleep and spikes and waves of convulsive activity were studied. 3. 3. Most surface positive spindles cannot be seen in monopolar leads, whereas negative spindles are fairly well picked up, but their electrical sign is frequently reversed. 4. 4. Recording of slow waves by a monopolar derivation chiefly depends on their cortical diffusion. A given cortical extension of the slow waves provides the best probability for monopolar recording. 5. 5. With regard to epileptic activity, the main result is that the electrical sign of surface positive spikes appears to be reversed in monopolar records. Surface negative spikes or waves usually keep their polarity. 6. 6. For any pattern of activity the monopolar lead frequently picks up electrical events originating from areas distant from the recording point. 7. 7. Although monopolar leads gave roughly the same results whether the electrode was on the surface of the cortex, dura, skull or on the scalp, a few differences where observed, depending on the exact site of the electrode. 8. 8. The results show that the classic monopolar electrode can either lessen the amplitude of electrical events in the underlying cortex, or suppress them or reverse their electrical sign, or pick up activities occurring in remote areas. 9. 9. An interpretation of these results is proposed, in which the size of the active cortical area and its position with respect to the recording electrode, play the main roles.