The most popular reason is because the soul is or mind is evidenced as a collection of electromagnetic frequencies called brain waves which are activated and controlled by both conscious awareness or sentient control as well as automatically.
This may seem amazing, but the entire system of electromagnetic conductive systems in the body is referred to as the Central and Peripheral nervous system (CNS & PNS). The CNS is generally the part of you which is conscious while the PNS is automatic like breathing.
When we sleep the CNS, which composes the brain, the brain stem, and the spinal cord, changes but the PNS remains active and constant.
You see, In order to explain how the mind relates to the body, I actually don't have to use new theories or information. It can be done using existing and old ones. Some idea's on duality are old as human's themselves you know. Yin Yang, for example, has been around since, at the very least, recorded history or about 6 thousand years. Yin-Yang is a symbol of universal energy and duality.
Energy in the body is I think what fascinates us most. Energy propagates as waves through space-time which is directly indetectable as a substance or thing, however we can measure it's effects [Wave Nature]. As a result, we have discovered that there is a kind of symphony being played out in our heads. A note in this symphony can represent a thought or idea. At any one time, our brains are processing information when thinking about a subject. Much of the information is either already organized, or in the process of being organized, so, like a real symphony, there is a definite rhythm and flow to our thoughts.
Thought is essentially a collection of brain waves. Each time you produce a thought or think about something, you are sending impulses of information along nerve pathways. These impulses or brain waves are typically divided into four groups that represent a category which describes our state of being during the various brain wave frequencies. The frequencies of a normal human can be said to range between 0 & 40 Hz. but it is not altogether clear and definitions vary. Typically the categories are thus:
Delta
0-4 Hz
Deep sleep
Theta
4-7 Hz
Light sleep
Theta frequencies are supposed Associated with relaxation, meditation, and creativity. For many people and proponents of binaural's, theta waves are a favorite.
Alpha
8-12 Hz
Alpha is said to be the brain waves that are dominant in the relaxed or normal state of mind.
Beta
12-30Hz
Awake. Beta generally responds to the point when you actually feel awake in your day.
Gamma
30+hz
(?)
What happens in Gamma state? Is it unhealthy? Is it useful in any way? We simply don't yet know, as most ideas are hypothesis which don't have a lot of evidence.
