John Carew Eccles

John Carew Eccles (Northcote, Victoria, 1903 – Locarno, Switzerland, 1997) was an Australian neurophysiologist who spent much of his career studying the synapse and, later, the relationship between mind and brain. He shared the 1963 Nobel Prize in Physiology or Medicine with Alan Lloyd Hodgkin and Andrew Huxley. Although he is remembered as a scientist, his philosophical work belongs to the twentieth-century debate about consciousness.

He studied medicine at the University of Melbourne and graduated in 1925 with first-class honours. As a student he found no satisfactory account of how mind and body interact, and this pushed him towards neuroscience. A Rhodes Scholarship took him to Oxford, where he worked under Charles Scott Sherrington and completed his doctorate in 1929. In 1937 he returned to Australia to direct the Kanematsu Institute at Sydney Medical School. After the war he taught in New Zealand and, from 1952 to 1962, at the Australian National University in Canberra. He later held posts in Chicago and Buffalo.

His best-known experiments used the stretch reflex as a model, a circuit of only two neurones. Stimulating the sensory neurone of the quadriceps produced a small excitatory potential in the motor neurone; enough of these summed together could make it fire and contract the muscle, while inhibitory potentials subtracted from that sum. Early on, Eccles argued that synaptic transmission was mainly electrical, a view that proved mistaken, but the debate it provoked led to experiments that demonstrated chemical transmission. With Bernard Katz he also helped clarify the role of acetylcholine as a neurotransmitter.

In his later years he turned increasingly to philosophy. Working closely with Karl Popper, he defended an interactionist dualism in which mind and brain are distinct realities that influence each other. Eccles described himself as a Catholic, and his position drew criticism from materialists. In 1977 he delivered the Gifford Lectures at the University of Edinburgh, titled "The Human Mystery" and "The Human Psyche".

His influence appears in two areas. In neurophysiology, his work on synapses helped lay foundations for modern neuroscience. In philosophy, his defence of interactionism remains a reference point against monist accounts of consciousness.