I haven't come into contact with any convincing evidence either way, but I have run across a few fun facts:
- Gray Barker's well-known published encounter happened in 1953, the year before the approval of chlorpromazine that marked the downturn in popularity of lobotomies
- According to Wikipedia, modern sightings started in 1947. The first trans-orbital lobotomy was in 1946.
"Post-operative blunting of the personality, apathy, and irresponsibility are the rule rather than the exception. Other side effects include distractibility, childishness, facetiousness, lack of tact or discipline, and post-operative incontinence."
Now, what does that remind you of?
In terms of popular culture associations, I am certainly not the first to make a link. In the film Repo Man, the character J. Frank Parnell is closer to the typical representation of an MIB than the characters cast as MIBs -- he is a former government employee who defected and got (you guessed it) a lobotomy.