Positronic brain

A positronic brain was a form of artificial brain.

Daleks
In 1940s, the Daleks created a human-cyborg scientist Bracewell, that was implanted into the British scientific community to develop technology for the war effort. The creation was said to be controlled by a positronic brain. (TV: Victory of the Daleks)

On Vulcan, the human space colonist Lesterson examined "dead" Daleks and, thinking of them as robots, conjectured they possessed a sort of positronic brain. (TV: The Power of the Daleks)

When the Second Doctor was forced to work for the Daleks in extracting the "human factor" from Jamie's emotions, he imprinted it into a positronic brain. This was to be implanted in the Daleks, which the Daleks hoped would have made them invincible. (TV: The Evil of the Daleks)

Other references
The Fourth Doctor recognized the labyrinth-like building complex that served as the lair of the Nimons as resembling both physically and functionally a "giant positronic circuit". (TV: The Horns of Nimon)

Behind the scenes
A positronic brain is a fictional technological device, originally conceived by science fiction writer Isaac Asimov (1920-1992). Its role was to serve as a central computer for a robot, and, in some unspecified way, to provide it with a form of consciousness recognizable to humans. When Asimov wrote his first robot stories in 1939 and '40, the positron was a newly discovered particle and so the buzz word positronic — coined by analogy with electronic — added a contemporary gloss of popular science to the concept.