A machine is an artifact. It is a human-built assembly of materials that have no natural inclination to work in unison. Silicon and copper, plastic and glass have no natural propensity to compute. We make artifacts, for example computers, out of these materials to serve our purposes. But they are not the materials’ natural purposes.
In the classical hylemorphic (Aristotelian) perspective, an artifact is an artificial composite of substances and thus it has an accidental, not substantial, form. Machines work as they do “accidentally”; that is, their function as machines is not inherent to the matter that comprises them. Rather their function is imposed on the disparate parts by human intelligence.
Unlike a machine, the brain is an organ, a functional part of a living organism. It (along with the body) has a substantial form; its activity is natural to it. One might say that the brain's activity is intrinsic to it, not imposed on it extrinsically, as is the activity of a machine.[1]
[1] https://mindmatters.ai/2018/10/yes-your-brain-is-a-machine-i...