A mind limited to or obsessed with a single idea, theme, etc (1927+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with one-track mind
A mind limited to only one line of thought or action, as in All you think about is sex—you have a one-track mind. This expression, alluding to a train that runs only on one track or in one direction, was first recorded in 1928.