XI Brain Imaging

While philosophers have, for centuries, pondered upon the relation between mind and brain, neuroscientists have only recently been able to explore the connection analytically — to peer inside the black box. This ability stems from recent advances in technology and emerging neuroimaging modalities. It is now possible not only to produce remarkably detailed images of the brain’s structure (i.e. anatomical imaging) but also to capture images of the physiology associated with mental processes (i.e. functional imaging). We are able to see how specific regions of the brain ‘light up’ when activities such as reading this book are performed, and how our neurons and their elaborate cast of supporting cells organize and coordinate their tasks. As demonstrated in the other chapters of this book, the mapping of the human mind (mostly by measuring regional changes in blood flow, initially by positron emission tomography (PET) and recently by functional magnetic resonance imaging or (fMRI)) has provided insight into the functional neuroanatomy of neuropsychiatric diseases. Amazingly, the idea that regional cerebral blood flow (rCBF) is related intimately to brain function goes back more than a century. As is often the case in science, this idea was initially the result of unexpected observations. The Italian physiologist Angelo Mosso first expressed the idea while studying pulsations of the living human brain that keep pace with the heartbeat (Mosso, 1881). These brain pulsations can be observed on the surface of the fontanelles in newborn children. Mosso believed that they reflected blood flow to the brain. He observed similar pulsations in an adult with a post-traumatic skull defect over the frontal lobes. While studying this subject, a peasant named Bertino, Mosso observed a sudden increase in the magnitude of the ‘brain’s heart-beats’ when the church bells signalled 12 o’clock, the time for a required prayer. The changes in brain pulsations occurred independently of any change in pulsations in the forearm. Mosso understood that the bells had reminded Bertino of his obligation to say a silent Ave Maria. Intrigued by this observation, Mosso then asked Bertino to perform a mental calculation; again, he observed an increase in pulsations and, presumably, blood flow as the subject began the calculation and a second rise just as he answered. This was the first study ever to suggest that measurement of cerebral blood flow might be a way of assessing human cognition. Charles Roy and Charles Sherrington characterized this relationship further at Cambridge University. Based on animal experiments, they suggested that ‘the brain possesses an intrinsic mechanism by which its vascular supply can be varied locally in correspondence with local variations of functional activity’. Their observations were fundamental, and their brilliant deductions have dominated the brain-imaging field since. One of the most extraordinary examples of the relationship posited by Roy and Sherrington was observed in Walter K., a German-American sailor who consulted Dr John Fulton at Boston’s neurosurgery clinic for headache and failing vision. Walter also reported to hear a humming noise in his head. Fulton, when listening with a stethoscope at the back of his patient’s head, confirmed this bruit and organized an exploratory intervention. Dr Harvey Cushing performed the neurosurgery and found a large arteriovenous malformation overlying the visual cortex. An attempt to remove the vascular malformation failed and left Walter with a bony defect overlying his visual cortex. His physicians could now hear the bruit even more clearly. During the course of his stay, Walter mentioned that the noise in his head became louder when he was using his eyes. As Fulton (1928) published later in the journal Brain: