I don't know quite what you mean by 'one-way'. Body and brain are mutually dependent parts of a single system; the processes of the body provide information about the world and its own inner state to the brain, and ensures the brain can work effectively, and the processes of the brain have overall command and control of gross bodily activities. Neither can function without the other.
You can describe a human in a variety of ways, depending on what aspects you want to concentrate on: a quantum system; a collection of atoms, water and chemicals; a collection of cells; an ecology of organisms, a biological machine, a system of many subsystems, a collection of organs, an animal, a person, a friend, a member of society; and so-on.
All are valid descriptions, but each has its own descriptive concepts and language, and it doesn't make sense to mix different descriptions that refer to different levels of emergence because emergent properties don't exist at the level from which they're emergent. So an animal may consist of a collection of atoms, but it doesn't make sense to discuss an animal's characteristics and behaviour in terms of its atoms any more than it makes sense to talk about the temperature and pressure in a room in terms of the velocities of its gas molecules.
When we talk about the human mind, we're talking about the emergent properties of the interactions of ~84 billion neurons and associated cells; human emotions, drives, goals, sensibilities, etc., are all facets of the mind that is emergent from those patterns of activity.