The development and evolution of "cerebral thermometry": The physiology underlying a nineteenth-century approach to cerebral localization and neurological diagnosis

Surface thermometers were developed in the latter half of the nineteenth century. From the 1850s through the 1880s, collaborations between physicians, research scientists, and instrument makers produced clear improvements in the technology to measure cranial surface temperatures, with development of self-registering mercury surface thermometers resistant to pressure and little influenced by ambient temperature, apparatus for recording cranial surface temperatures from multiple stations simultaneously, and development of thermoelectric apparatus. Physiologic studies of cranial surface thermometry were conducted over a quarter century from 1861 to 1886. Beginning in the 1860s Albers in Bonn, Germany, and Lombard at Harvard and later in England systematically investigated surface temperatures on the head using surface thermometers and thermoelectric apparatus; they demonstrated that head temperatures were variable over time and across individuals and were not clearly influenced by thinking or muscular contraction but were influenced by ambient air temperature. In 1880 Amidon in the United States claimed that cranial surface thermometry during exertion produced localized increases in surface temperature on the contralateral scalp in a specific pattern ("external motive areas") indicating underlying brain areas responsible for each movement. Amidon's results were not reproduced by experienced physiologists in England or France. Contemporaries recognized that significant technical and practical problems limited the accuracy and reliability of cranial surface thermometry. Physiological studies of cranial surface thermometry ended in the mid 1880s, although some clinicians who were early advocates promoted its use in clinical contexts into the early twentieth century.