No brain, no cognitive functions, is a good place to start the discussion.
How do you say cognitive functions exist, if not as brain states and processes? Please be specific so that any impartial onlooker can test the correctness of your answer.
We are brain / body. Spirit, in the sense of a supernatural element or soul, exists only as a concept / thing imagined in an individual brain. Not the slightest examinable evidence suggests otherwise.
We can start a conversation about mind at the level of physical activity in the chemistry of the brain, if you wish. But if you are not prepared even to contemplate moving on from that starting point, the conversation isn't going anywhere.
Consciousness exists experientially, and this experience of being conscious, of being sentient and aware, has qualities of it's own, qualities unique to itself. To reduce this experience entirely to electrical and chemical activity in the brain, is to dismiss those qualities of consciousness which by definition, are functions of the mind. The electro magnetic spectrum of light, and the capacity of the eye to perceive it, may explain the physics of colour. But that does not explain the
experience of seeing red, or blue, or green.
We are mind, body and spirit. The brain is an organ in the body. The mind is a phenomenon of it's own, though it may originate in that magnificently complex organ, the brain. And the spirit is the life force, without which the body would be inanimate. You simply cannot reduce these three aspects of being into one, without losing sight of something important. To reduce everything to the material, is to build a house without a window.