1898–1969 · neurophysiologist, Yale, Illinois, MIT

arren Sturgis McCulloch trained in philosophy, psychology and medicine, and worked as a neurophysiologist at Yale, the University of Illinois in Chicago and, from 1952, MIT's Research Laboratory of Electronics. He chaired the Macy conferences on cybernetics (Heims, 1991).

what he did

With the young logician Walter Pitts he wrote "A logical calculus of the ideas immanent in nervous activity" (McCulloch & Pitts, 1943), which treated neurons as all-or-none threshold units and showed that networks of them could compute logical functions; with memory added, they claimed, such nets could compute what a Turing machine can [paraphrase, not a quotation]. Piccinini (2004) argues it was the first computational theory of mind and brain. Later, with Lettvin, Maturana and Pitts, he showed that a frog's retina sends the brain already-processed signals, such as for small moving dark objects (Lettvin et al., 1959).

McCulloch–Pitts threshold unit, 1943: all-or-none inputs, excitation, inhibition as a veto, a threshold, and an output that fires or does not McCulloch & Pitts, 1943. Drawn by script. credits

what is argued about

The 1943 neuron was an idealisation that real neurons do not obey, and the paper's notation was famously hard to follow. Abraham (2002) traces its origins in mathematical logic, philosophy and the physiology of the time; von Neumann's 1945 report on computer design borrowed its neurons as idealised switches. Whether it was neuroscience, logic or a manifesto is still discussed.

why he is here

Every artificial neural network descends, through the perceptron, from the McCulloch–Pitts unit.

in the tour: the room called "Governors and feedback" has a placard called "McCulloch and Pitts, 1943" ···

Primary works and sources

1. Heims (1991). The Cybernetics Group. Cambridge, MA: MIT Press.
2. McCulloch & Pitts (1943). A logical calculus of the ideas immanent in nervous activity. The Bulletin of Mathematical Biophysics. doi:10.1007/BF02478259
3. Piccinini (2004). The First Computational Theory of Mind and Brain: A Close Look at Mcculloch and Pitts's “Logical Calculus of Ideas Immanent in Nervous Activity”. Synthese. doi:10.1023/B:SYNT.0000043018.52445.3e
4. Lettvin et al. (1959). What the Frog's Eye Tells the Frog's Brain. Proceedings of the IRE. doi:10.1109/JRPROC.1959.287207
5. Abraham (2002). (Physio)logical circuits: The intellectual origins of the McCulloch–Pitts neural networks. Journal of the History of the Behavioral Sciences. doi:10.1002/jhbs.1094

see also

	archive: the perceptron, 1958 — what came next
	timeline: cybernetics
	timeline: machines that answer
	Walter Pitts — the other author of 1943
	Jerome Lettvin — the frog, and the friend
	essay: the break — what happened in 1951 or 1952