A mind probe was a device which allowed an operator to extract information from a subject's mind through the use of some kind of projected energy.
The Third Doctor once told Jo that he had found a way to defeat mind probes, and quipped that he'd once destroyed a government's entire supply of probes. Later, when hooked up to an Earth Security mind probe, he demonstrated that his brain could destroy their versions as well. (TV: Frontier in Space)
A mind probe of Gallifreyan design was going to be used on the Castellan to discover the truth about the Black Scrolls of Rassilon, but he was shot before they could use it on him. Nevertheless, he exhibited great fear of the mind probe, which perhaps hinted at its power against the Time Lord brain. (TV: The Five Doctors)
Torchwood Three also had a mind probe. They used it on Beth Halloran when they were trying to discover whether she had attacked the burglars who broke into her house. Ianto remarked that the last alien they used it on exploded. (TV: Sleeper)
During the Last Great Time War, two members of the High Council of the Time Lords on Gallifrey, Karlax and the Castellan, administered the probe to Cinder. Although human, she managed to survive it. (PROSE: Engines of War)