The Fourth Doctor told Leela that his brain's "Reflex Link" allowed him to tune into the telepathic network of "the Time Lord intelligentsia", which amounted to "a thousand super-brains". (TV: The Invisible Enemy (part 3) [+]Loading...{"part":"3","1":"The Invisible Enemy (TV story)"})
Behind the scenes
Strictly speaking, the term "intelligentsia" does not refer to any kind of hive mind, but rather to a societal upper crust; it is not clear whether the use of the term in The Invisible Enemy was intended in this sense, with the Doctor's statement's meaning being that he could mind-link with a special elite of a thousand among the Time Lords, or if Bob Baker and Dave Martin were harkening back to the etymology of the term "intelligentsia" as relating to intelligence, and intended for "the Time Lord intelligentsia" to be a name for the Time Lord hive mind itself.