The Cannon-Marañón Correspondence and the Autonomic Physiology of Emotion (1919-1936)

Between 1919 and 1936, American physiologist Walter B. Cannon and Spanish physician Gregorio Marañón engaged in a sustained transatlantic correspondence that shed light on emerging ideas about the physiologic basis of emotion. Drawing on letters preserved at Harvard's Countway Library of Medicine and the Fundación Ortega-Marañón in Madrid, we examine how their dialogue bridged experimental physiology and clinical neuroendocrinology during a formative era in modern neuroscience. Cannon, widely known for introducing the concepts of "homeostasis" and the "fight-or-flight" response, saw in Marañón's clinical observations a compelling complement to his laboratory findings. In particular, Cannon repeatedly cited Marañón's work on the emotional effects of adrenaline, which distinguished between purely physiologic visceral reactions without subjective emotion ("cold emotion") and full subjective emotional states ("hot emotion"). This nuanced differentiation anticipated later cognitive and constructivist theories of emotion. Their exchange helped shape foundational concepts in affective and autonomic neuroscience by linking internal affective states to neuroendocrine mechanisms and observable bodily responses. These ideas would later cohere in Cannon's The Wisdom of the Body (1932), where traces of their correspondence are evident. Beyond their scientific importance, the Cannon-Marañón letters offer a rare window into the international and interdisciplinary networks that shaped biomedical thought in the early 20th century. It also reflects broader commitments because both men had a relevant political involvement. By recovering this epistolary exchange, we shed light on an overlooked chapter in the history of neuroscience and the enduring value of scientific dialogue.