Cortical Blood Flow Related to EEG Patterns Evoked by Stimulation of the Brain Stem

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Abstract
Summary.: 1. The cortical blood flow was recorded in lightly anesthetized or unanesthetized (encéphale isolé) cat preparations in which different EEG effects were elicited by electrical stimulation of the brain stem.2. The regular EEG ‘arousal reaction’ (‘cortical activation’) was followed by a marked increase of the cortical blood flow which was due to a reduction of the cortical vascular resistance (Ingvar 1955b, Ingvar and Söderberg 1956b).3. From this was distinguished another type of EEG response, the ‘flattening reaction’, characterized by reduction of amplitude with only occasional slow waves, differing significantly from the other by the fact that no cortical vasomotor changes were found to accompany it. Respiratory and systemic circulatory changes, as well as effects upon the muscle tone concomitant to the brain stem stimulation were not related to this response. It also seems unlikely that local vasoconstrictions could explain it. For these reasons it is set off as a specific reaction.4. It was confirmed that ‘sleep spindles’ could be elicited by electrical stimulation of the brain stem. No cortical vasomotor changes could be recorded during such responses. Physiological sleep was not studied.5. A fourth type of response was characterized by generalized high voltage slow waves. It often occurred during systemic circulatory failure and possibly had some relation to a defective cortical circulatory homeostasis and to the development of brain edema, seen in such cases.

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