This is the only episode of the series with a main character's name in the title. There are fifteen title drops, and twenty-one additional uses of the word "brain" besides.
William Shatner called this one of the series' worst episodes, calling the episode's plot a "tribute" to NBC executives who slashed the show's budget and placed it in a bad time slot. In his memoir Star Trek Memories, he wrote that filming the episode filled the entire cast with a sense of looming dread.
Leonard Nimoy wrote: "Frankly during the entire shooting of that episode, I was embarrassed - a feeling that overcame me many times during the final season of Star Trek".
Scotty uses McCoy's computer in sickbay to find out how to make Spock ambulatory.
The mechanically moved Spock is brought to the bridge by McCoy and Scotty before the landing party beams down to Sigma Draconis VI.
An ending scene on the bridge (with an apparent pun to end the episode) is present in the final draft script. It is unknown if the scene was filmed and cut from the finished episode or was scrapped entirely.
The remote control McCoy uses to control Spock's brainless body was modified from one of Wah Chang's original communicator props from "The Cage".
The jumpsuit that Spock wears on the planet's surface appears to have been the same one he wore in "This Side of Paradise", complete with black shirt.
Recycled Script: The Star Trek: Enterprise episode "Dead Stop" reused the concept but made sure to play it for horror, have the entire person be abducted, and drop the brainless fanservice beauties altogether.
Technology Marches On: The ion drive that impresses the warp-equipped Federation is possible with today's technology (though it wouldn't be as powerful as it's depicted).
Throw It In!: This episode may have gotten to the point of being a camp classic because of this trope. Gene Coon, who wrote this under his "Lee Cronin" pseudonym, since he had left Desilu for Universal and could thus not, contractually, write for the show under his own name, had already delivered six scripts for the season when Gene Roddenberry asked him for yet one more. Annoyed, Coon supposedly wrote "Spock's Brain" as a pointed parody of what he saw as Roddenberry's limited understanding of science fiction as a whole, and may well have not expected, for this reason, that the episode would actually be produced. But apparently the show was too desperate for scripts for anyone to pick this up and ask for a rewrite.
What Could Have Been: Based on Gene Coon's story outline, this episode underwent significant revisions before the final draft. Among the early concepts:
Spock's brain was taken while he, Kirk, and McCoy were exploring the surface of an asteroid.
The antagonists were from the planet "Nefel," and were known as the "Nefelese." Their leader is a male named "Ehr Von." Also, there is no mention of the "Teacher."
When Kirk contacts Spock's brain, he instructs the brain to go into the slon porra, the Vulcan state of complete mental control.
McCoy received no transfusion of any special surgical knowledge except for a study of the planet's advanced surgical techniques. Only when combined with his existing surgical knowledge is he then able to perform the surgery.
After McCoy completes the brain implant surgery, Spock experiences several side effects from McCoy having reversed the connections of several nerve endings, causing Spock to, among other things, laugh when he wants to sneeze. He is, however, able to restore the errors with his own mental disciplines.
Writer Revolt: The legend goes that Gene Coon, responsible for several very good episodes of the show, wrote a deliberately terrible script in protest of Fred Freiberger becoming the new show runner, to display his fear of what the show would become under the care of the guy who ran Lost in Space.note Which is interesting, considering that Freiberger never worked on that show And then it ended up getting made anyway.
(even down to the agony-causing wrist gadget and BOING! sound) for a Mars and Venus Gender Contrast.