Origin of temperature changes evoked in the brain by sensory stimulation

Abstract

Temperature was measured in lateral geniculate nucleus, ventrobasal thalamus and inferior colliculus and at the cerebral arteries which supply these structures in monkeys and cats with chronically implanted thermocouples. Animals were studied when they were conscious and when they were anesthetized, during spontaneously occurring changes in behavior and during the presentation of visual, somesthetic, and auditory stimuli. Parallel low-gain and high-gain recorders allowed absolute temperatures to be determined with an accuracy of 0.05 C and temperature changes of 0.0004 C to be resolved. In confirmation of earlier studies, we found that in behaving animals, large changes in temperature occur in cerebral arterial blood and throughout the brain during feeding, sleeping, and arousal. Brain temperature shifts follow blood temperature shifts. The cerebral arterial blood at the circle of Willis is cooler than the brain. When sensory stimuli are presented, the usual thermal response is a rise in temperature at the cerebral arteries followed by a smaller rise in brain temperature. The changes in cerebral arterial blood temperature following sensory stimulation ranged from 0.003 C to 0.133 C in lightly anesthetized animals. The temperature changes in lateral geniculate, ventrobasal thalamus, or inferior colliculus ranged from 0 to 0.067 C and followed the blood temperature changes by 7 to 71 sec. Changes in brain temperature never occurred without a previous change in blood temperature. Blood temperature responses to sensory stimulation were larger in awake animals and in light anesthesia than in deeply anesthetized animals. Blood temperature rises were associated with peripheral cranial vasoconstriction, suggesting that the initial thermal response to sensory stimulation is peripheral autonomic activity and decreased peripheral heat loss. Other investigators observing brain temperature changes following sensory stimulation did not measure cerebral arterial blood temperature and concluded that the shifts in brain temperature were due to changes in neuronal metabolism or cerebral blood flow. The results of the present study do not support this conclusion. When cerebral arterial blood temperature and brain temperature are monitored simultaneously, it is evident that the changes in brain temperature elicited by sensory stimulation are produced by changes in temperature of the cerebral arterial blood.