In this work Angelo Mosso reported his discovery that blood circulation in the brain increases in certain discrete areas during mental activity, and published the records of this activity produced by the machine he invented to record these changes. As the first method of imaging brain function, Mosso's work paved the way for modern-day brain imaging techniques such as CT scans, PET scans and magnetic resonance imaging.
“. . . Mosso was the first to experiment with the idea that changes in the flow of blood in the brain might provide a way of assessing brain function during mental activity. Mosso knew that, in newborn children, the fontanelles—the soft areas on a baby’s head where the bones of the skull are not yet fused—can be seen to pulsate with the rhythm of the heartbeat. He noticed similar pulsations in two adults who had suffered head injuries that left them with defects of the skull, and observed, in particular, a sudden increase in the magnitude of those pulsations when the subjects engaged in mental activities” (Kolb & Whishaw, Fundamentals of Human Neuropsychology, 132).
Mosso devised a graphic recorder to document these pulsations, demonstrating that blood pressure changes in the brain caused by mental exertion occur independently of any pressure changes in the rest of the body. Mosso concluded that brain circulation changes selectively in accordance with mental activity, stating that “we must suppose a very delicate adjustment whereby the circulation follows the needs of the cerebral activity. Blood very likely may rush to each region of the cortex according as it is most active” (quoted in Shepherd, Creating Modern Neuroscience, 185). English translation in M. E. Raichle and G. M. Shepherd, Angelo Mosso's Circulation of Blood in the Human Brain (New York: Oxford Univ. Press, 2014.)