Concerning body awareness how I've heard it put and quite succinctly is place body on cushion and then mind in body. Whether I'm practicing mindfulness of breath, sound or smell or effortless or loving-kindness and sometimes even candle gazing I have a warm-up. After seated comfortably take a few slow and deep breaths and then do a body scan, starting at the feet and moving up to the crown, sensing tension on the inhale and releasing tension on the exhale.

For the breath awareness I practice (Shamatha/Calm Abiding) and from the instructions I found all those years back this is the neuro-physiology it explains is at work behind the scenes.

In the western world we are trained from an early age to identify with our intellect and thinking. We all, to a greater or lesser extent, "live in our heads". The furniture we use, the ways we use it and the habits of body and mind we accumulate add to this imbalance. This practice of paying attention to bodily sensations as we breathe in and out, and calming the body as we do so, whilst learning not to identify with thoughts has a strong backing in Neuro-Physiology.

One of the most important features and reasons for the success of the practice is that it re-embodies us: that is to say that it reconnects our body and mind - our bodymind.
The brain has twelve pairs of nerves that enter directly into the brainstem bypassing the spinal cord. Most of these nerves serve functions in the head and face: smell, hearing, sight, etc.

The tenth "Cranial" nerve, the Vagus nerve or "wanderer", exits the skull through the Jugular foramen, a hole in the base of the skull. It is one of only two of these pairs of Cranial nerves that enters the body. The Vagus nerve has branches that connect to the ears and larynx and it plays a significant role in speech and language comprehension through these. It then travels down the neck inside the back of the throat and enters the chest cavity. It provides feedback to the brain from the lungs and heart including blood pressure, oxygen and carbon dioxide content of the blood (via the Aortic receptors).

The Vagus also provides feedback to the brain from all the internal bodily organs in our abdomen and plays a pivotal role in controlling the stomach and the pancreas. It has strong links to all of the main nerve plexuses (groups of nerves like mini-brains) in the body.

It is clear to see that with connections to language and thinking (through the branches to the ears and larynx), breathing and heart (including bodily stress-levels) through the branches to the lungs, heart and Aortic receptors, emotions and feelings which actually arise in the body when we become aware (through the strong links to abdominal organs and especially stomach - hence the expression such as "gut feelings"), that the Vagus nerve is the information super-highway that links body and mind into one: bodymind, that links the physical to the intellectual through it's expression of feeling, animal instinct and involvement of language.

This practice revitalises and fully activates the Vagus nerve in a very direct manner. It is the principal Neuro-Physiological mechanism through which the practice works due to the nerve's connections to the functions the practice changes: bodily and mental stress levels (or level of calm) thinking, awareness of the bodymind as one connected entity - as opposed to the sense of the body being separate from the mind. Additionally, and over time, many other positive changes will occur to brain function and Neuro-Chemistry as a result of this practice. Scientific research has begun to document these quite widely.