Beyond descriptive neurology: Broca, cerebral hemodynamics, and cortical function

Pierre-Paul Broca's studies in neurobiology remain of interest. I review a previously neglected aspect of Broca's work in which he presages the use of modern scanning techniques. Broca's goal was to correlate cerebral metabolism to regional cerebral blood flow (CBF) using a novel method, to which he referred as cerebral thermometry. Broca attempted to measure changes in temperatures from the ischemic area and across the watershed regions during a stroke, and the increased CBF produced by performing a cognitive task such as reading aloud. The method involved measurements of local temperatures at specific points about the head with an array of strategically placed thermometers much as EEG electrodes are arrayed to record the electrical activity of the brain. Although his technique was inaccurate and unreliable, the concept of measuring CBF as a diagnostic aid and as a cognitive research tool was prescient. Broca's limitation was not conceptual but purely technological. Broca's attempt to measure CBF as a surrogate for cerebral metabolism was conceptually valid but premature because he lacked the technology necessary to do so.