Electroencephalography

Electroencephalography, or EEG, was an Earth technology able to register the electrical activity of the brain (TV: Spearhead from Space) and show the brainwaves of an individual. (TV: Planet of the Spiders)

While in a self-induced coma post-regeneration, the test was made on the Third Doctor, showing no activity. (TV: Spearhead from Space)

The Third Doctor performed such a test on the clairvoyant Herbert Clegg. (TV: Planet of the Spiders)

The technology of the Kaled security scan was able to perform an EEG on the instant. It demonstrated that the Fourth Doctor and Harry Sullivan weren't native of Skaro. (TV: Genesis of the Daleks)