Fig. 1.

Normal responsiveness of cortical neurons and glia to cortical stimulation. A, Top view of cat's brain with the localization of association areas 5 and 7 in the suprasylvian gyrus. B, The impalement of a glial cell is marked (open arrowhead) by a sudden voltage deflection from extracellular potential values (∼0 mV) to −80 mV. Intraglial potentials (slow depolarizations) are reversed with respect to the extracellular ones. C, Double intracellular (neuron–glia) and field potential recording in cortical area 5. Response to a single cortical shock (black triangle) delivered close to the field electrode. The recording sites correspond to those indicated in A. The neuronal response consisted of an initial depolarization crowned by action potentials, an inhibitory potential, and a rebound excitation. The corresponding responses in the glia were a sluggish depolarizing slope, a slow further depolarization, and a negative wave, respectively. This shape was reproduced in the depth-EEG recording, with the exception of the early response, which appeared as a negative potential.D, Average of 25 responses evoked by the cortical stimulation. The initial glial depolarization (a) is clearly separated from the following positive wave (b) by a change of the depolarizing slope. In this and the following figures, all potentials are presented with the positivity upward. Intracellular recordings are all at rest (zero current), unless expressly indicated, and the resting membrane potential is indicated at left.