Intracellular Recordings from the Motor Cortex during EEG Arousal in Unanaesthetized Brain Preparations of the Cat

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Abstract
Intracellular recordings were made from 92 neurons in the precruciate cortex of encephale isole and midpontine pretrigeminal preparations of the cat. All but 1 of these cells showed appreciable changes in the membrane potential during the transition from the cortical slow wave phase to the EEG arousal occurring spontaneously or induced by stimulating the midbrain reticular formation. Thus, 38 cells were depolarized (D-type cells), 48 cells hyperpolarized (H-type cells) and 5 cells showed an early hyperpolarization and a later depolarization (mixed type). The latency of intracellular responses to reticular stimulation was shorter in the D-type cells than the H-type or mixed-type cells, and shorter for each of the D- and H-types in the cells of the superficial layers than those of the deep layers. The D-type cells were distributed widely through laminae I-V, but the majority was sampled in lamina II. The H-type cells were located in laminae III-VI with the mode at the upper half of lamina III. The mixed-type cells were mostly located in laminae V and VI. Antidromically identified slow pyramidal tract (PT) cells (n = 9) all belonged to the D-type, and fast PT cells either to the H- (n = 11) or the mixed type (n = 4). The EEG arousal apparently is a state composed of both excitatory and inhibitory responses of cortical cells which are processed from the superficial to the deep layers.