In Canto Two of his poem John Shade (the poet in VN's novel Pale Fire, 1962) tells about Aunt Maud's mental illness and mentions the monsters in her brain:
Maud Shade was eighty when a sudden hush
Fell on her life. We saw the angry flush
And torsion of paralysis assail
Her noble cheek. We moved her to Pinedale,
Famed for its sanitarium. There she'd sit
In the glassed sun and watch the fly that lit
Upon her dress and then upon her wrist.
Her mind kept fading in the growing mist.