A sudden inability to finish a thought, or to recall what the thought was. Often indicates the presence of a mental illness such as schizophrenia.
Example: In the middle of talking about his childhood, the patient abruptly pauses, after which he can’t remember what he was saying.
Grinnell, R. (2008). Thought Blocking. Psych Central. Retrieved on April 25, 2015, from http://psychcentral.com/encyclopedia/2008/thought-blocking/