The Effect of Mental Arithmetic on Cerebral Circulation and Metabolism 1

Considerable evidence exists to suggest that conscious mental activity is coupled to an active utilization of oxygen by the brain. When there is a deficiency in the oxygen supply to the brain, produced, for example, by anoxia or cerebral ischemia, consciousness is rapidly impaired (1, 2). Conversely, the depression of consciousness observed in various pathological states has been found to be accompanied by an appreciable re-duction in cerebral oxygen consumption (3-6). Indeed, there has been observed a striking paral-lelism between the level of conscious activity in these states and the rate of oxygen utilization by the brain (7). The fact that both cerebral oxygen consumption and conscious mental activity are concomitantly depressed in various non-physiologic states leaves unanswered, however, the question of whether the various mental activities which characterize the state of consciousness require energy derived from oxidative processes. It is conceivable that the oxygen required by the brain to sustain con-sciousness may be utilized only to maintain its structural and functional integrity without any oxygen being consumed by the actual mental processes themselves, in the sense that muscular work, either skeletal or cardiac, requires additional amounts of oxygen (8, 9). That such may be the case is suggested by the findings of Mangold and his associates that in natural sleep, a state of rela-tive unconsciousness unassociated with pathologic processes, cerebral oxygen consumption is un-changed from the normal waking state (10). Because of the nature of the phenomena, in-vestigations of mental processes are limited al-most exclusively to studies in unanesthetized man. IXThis investigation wasupported in part by a re-