ACTIVITY OF ISOCORTEX AND HIPPOCAMPUS: ELECTRICAL STUDIES WITH MICRO-ELECTRODES

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Abstract
Micro-electrode techniques suitable for examination of electrical changes in the nervous system are described. The following 2 predictions were verified by expts. on the isocortex and on the hippocampus: large potential differences should be recorded from micro-electrodes at certain positions in active tissue (i.e., close to active elements); under certain conditions micro-electrodes should record predominantly the activity of only a small vol. of tissue immediately adjacent to them. Deep pento-barbital anesthesia greatly simplifies the electrical patterns recorded from the isocortex (cat). Isolated voltage changes of considerable size and duration appear; they are probably due to organized activity in groups of related neurons. Further expts. on the hippocampus (cat, rabbit), which has relatively simple structure, show besides changes manifestly due to stimulation by injury 3 types of activity: "Slow waves," spontaneous excursions of 20 to 70 msec. duration, are recorded from the surface of the hippocampus as well as from micro-electrodes placed at various positions within it. Their nature is obscure but there is no evidence that they are composed of overlapping spike-like components. Rapid deflections of about 1 msec. in duration and always negative in their predominant phase are recorded only from micro-electrodes placed in or very near the strata containing the cell bodies of the pyramidal cells of the Ammonshorn. The stimulation of the afferent fibers going to the hippocampus from the area entorhinalis results in responses which may be recorded from the surface of the hippocampus and from points within it. The surface response ordinarily appears after a latency of one or a few msec. and is characterized by an inital surface positive phase (10 to 20 msec.) followed by a smaller, longer and more variable surface negative phase. The responses recorded from micro-electrodes inserted within the hippocampus appear of opposite sign when the micro-electrode (monopolar lead) is in the deeper parts of the Ammonshorn. In a significant atypical expt. the response was surface negative and reversed at a shallower depth in the hippocampus. The results were analyzed in terms of potential theory and the membrane hypothesis. The responses to stimulation are interpreted as due largely to potential changes characterizing the activity of the perikarya of the pyramidal cells of the Ammonshorn.

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