Is there any published lore that shows Mind Flayers can extract and farm brains?

Question

I was doing some research on Mind Flayers and read/heard that Mind Flayers will occasionally extract a brain and use it to research the effects of Psionics, and that they enjoyed the mad thoughts they produced (Though I cannot for the life of me find the source of where I read/heard it). I presume that due to the Elder Brain surviving in a brine pool that they would put some of that brine in a jar and preserve a brain alive in it...

...As an extension to this; would someone who can communicate telepathically then be able to actually speak with the brain in a jar (i.e. GOO warlock ability). I assume if they can, that the brain cannot respond as it cannot 'see' the one speaking to it.

My scenario being that my PC's will soon be fighting Mind Flayers, and if one of them gets their brain extracted, I would rather the Flayer choose to preserve it so that the party GOO warlock could potentially still speak to them but the party member could not respond. Mainly just to mess with them even more - nothing wrong with a little DM Schadenfreude.

My main concern with doing it is that it almost denies 'closure' of a character death. If, as a general rule, Mind Flayers don't/wouldn't 'farm' brains in any particular way then I'd prefer to keep it out of my game. If it's something well within their power and makes sense that they would be doing it; then it's on the players carelessness rather than me just being cruel for the sake of it

Answer 1

Yes, this is known to happen.

Illthids extracted victims' brains to create Intellect Devourers¹ whose larval form was Ustilgators². Brain was subject to some rituals allowing it to survive in brine pool. Such brains were later eaten as raw, pickled or seasoned with fungi delicacy - and remember, Illthids need brains that are alive.

If Ustilgator was not eaten, it then changed into Intellect Devourer. Intellect Devourers were often employed as guards, and Mind Flayers are known to be fearful and paranoid, so a recent encounter with adventurers is a good reason to start creating them.

Thus, you have a solid case for keeping extracted brain alive: guard or luxury food. And rituals may take some time, giving other PC time to talk to such brain or do other things with it.

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1. Monster Manual 5th edition p. 191 says Devourers are made from transformed humanoid brains.
2. Ustilgators exist since 1983 (Dragon magazine 69 page 36) but started as brainlike fungi. Dragon Magazine 337 page 34 defines them as larvae of Intellect Devourer.

Answer 2

Mind Flayers are known to extract brains, but usually to eventually turn them into Intellect Devourers. The brain would have to be preserved until then, of course.

Source - the 5e official Waterdeep: Dragon Heist adventure book (minor spoilers):

Nihiloor is a mind flayer that the players first encounter in an underground hideout (p. 28-29). They can later find him in the Xanathar faction's lair, in an area described as an Extraction Chamber (p. 110-111). He has Zaibon, a captive drow whose brain is to be replaced by an intellect devourer, and the text specifically says, "(Were Zaibon less useful, Nihiloor would have extracted his brain instead.)"