The response of the circulatory system to muscular work has been studied extensively. The effect of mental exertion on the intracranial circulation has received little attention because of the obvious difficulty of observing changes in the flow of blood through the brain of man.
By means of experiments with animals, many facts of importance concerning the intracranial circulation have been uncovered. For example, the extensive studies of Forbes and his co-workers1 have demonstrated that the arterioles of the pia can be made to dilate and constrict in response to stimulation of the vagus or sympathetic nerve or to alterations in the chemical constituents of the blood. Stimulation of cranial nerves also seems to be effective. Alexander2 threw a strong light on the retina of dogs, and by means of a plethysmograph and through measurements of the difference in the oxygen content of blood entering and leaving the brain,