Full Idea
Sensitive and rational matter …makes not only the Brain, but all Thoughts, Conceptions, Imaginations, Fancy, Understanding, Memory, Remembrance, and whatsoever motions are in the Head or Brain.
Gist of Idea
The brain, and all the mental events within it, consists entirely of sensitive and rational matter
Source
Margaret Cavendish (Philosophical Letters [1664], p.185), quoted by Matthew Cobb - The Idea of the Brain 2
Book Reference
Cobb,Matthew: 'The Idea of the Brain' [Penguin 2020], p.42
A Reaction
Judging by the date of this, and that she is a Cavendish, the influence of Hobbes must be strong, which was brave in 1664. A very strong statement of reductive physicalism, making sure that nothing is left out.