Since next to nothing is known about the human body- it's as good a theory as any other.
No, it's not as good a theory as any other. There is zero evidence for it...zero. The more reasonable theory, based on what we know of brain anatomy and function, is that the brain is a self-contained organ of the human body, going about its work of keeping the body alive in a myriad of ways.
Well, you don't obviously believe in the concept of a spirit, so yes, that would seem absurd to you. Besides the reception/transmission sites could consist of just a handful of cells, or, several cells could share the function at several sites and multitask. Who knows. The brain is incredibly complex, and 4 dimensional.
The brain is the hardware, the spirit the software. Big deal- a spirit is just a piece of living software-- nothing unbelievable about it- just another piece of technology. Highly advanced, but still just a form of machine/device.