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Alan Turing was a visionary thinker on artificial intelligence (AI), devising the Turing test, which is still used as a key gauge of how close machines have come to human intelligence. He also published prescient ideas about simulating a brain with computers.

Toward the end of his life, he was also beginning tantalising work in biology, devising a mathematical theory of “morphogenesis” – in essence, how a leopard gets its spots

Artificial Brains

Turing was curious about the brain. He believed that the infant brain could be simulated on a computer. In 1948, he , and in doing so gave an early description of the artificial neural networks used to simulate neurons today.

His paper was prescient, but was not published until 1968 – years after his death – in part because his supervisor at the National Physical Laboratory, Charles Galton Darwin, described it as a “schoolboy essay”.

The paper describes a model of the brain based on simple processing units – neurons – that take two inputs and have a single output. They are connected together in a random fashion to make a vast network of interconnected units. The signals, passing along interconnections equivalent to the brain’s synapses, consisted of 1s or 0s. Today this is called a “boolean neural network”; Turing called it an unorganised A-type machine.

The A-type machine could not learn anything, so Turing used it as the basis for a teachable B-type machine. The B-type was identical to the A-type except that the interconnections between neurons had switches that…