UNIT ACTIVITY OF CENTRAL CEPHALIC BRAIN STEM IN EEG AROUSAL

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Abstract
Behavior of individual neurons in the central cephalic brain stem was explored during eeg synchrony, induced with small doses of chloralosane or midbrain lesions, and during eeg arousal, induced by afferent or central stimulation. Three main types of unit-response were elicited by single sciatic shocks. Units which discharged repetitively during the evoked potential were silent during the positive deflection and exhibited succeeding after-discharge. Units which did not fire in association with evoked potential were subsequently either caused to discharge or to discharge more frequently for several seconds. Less commonly, the frequency rate was decreased or the unit would stop firing briefly. Most often, repetitive sciatic stimulation led to a marked increase in frequency of resting discharge, with recruitment of previously silent units. Identical responses were induced by direct excitation of the brain stem arousal system or by physiological stimuli. After reaching a maximal frequency of 30-60/second, augmented firing declined gradually over periods as long as 30 seconds. Less often, during eeg arousal, units exhibited reduction of firing rate. The bearing of these findings on interpretation of eeg changes is varying. Instances of inhibition or reduction of neuronal firing favor the concept of blocking or suppression. Breakup of grouped firing associated with spindle burst waves supports that of desynchronization. The predominant observation of augmented firing and recruitment indicates that terms connoting an excitatory process, as "eeg arousal" or "activation," are the most appropriate.

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