The brain is connected to the body through chemical channels as well as neural channels:
The chemical bath in which all body cells live and of which the blood is an expression--the internal milieu--also ends up sending signals to the brain, not via nerves but via chemical molecules, which impinge directly on certain parts of the brain designed to receive their messages. The range of information conveyed to the brain in this manner is extremely wide. It includes, for example, the state of contraction or dilation of smooth muscles (the muscles that form the walls of the arteries, the gut, and the bronchi); the amount of oxygen and carbon dioxide concentrated locally in any region of the body; the temperature and the pH at various locations; the local presence of toxic chemical molecules; and so forth.
'Body loop': Mental states => brain states => body states => brain states => mental states
The idea here is that the body and brain are engaged in a continuous interaction that unfolds in time, within different regions of the body and within mental space as well. Mental states cause brain states, which cause body states; body states are then mapped in the brain and incorporated into the ongoing mental states. A small change on the brain side of the system can have major consequences for the body state (think of the release of a hormone); likewise, a small change on the body side (think of a knife cut, or a tooth infection, or the rupture of an ulcer) can have a major effect on the mind once the change is mapped as a nociceptive state and perceived as acute pain.
'As-if body loop': Unfolding emotion => body states constructed in advance before (or even instead of) the emotional change => brain/mental states:
But this is not the only network that links mind and body--there is another we call the 'as-if body loop.' Some fifteen years ago, Antonio proposed that in certain circumstances, as an emotion unfolds, the brain rapidly constructs maps of the body comparable to those that would result were the body actually changed by that emotion. The construction can occur well ahead of the emotional change, or even instead of the change. In other words, the brain can simulate a certain body state as if it were occurring; and because our perception of any body state is rooted in the body maps of the somatosensing regions, we perceive the body state as actually occurring even if it is not. (This functional arrangement can work for emotion because there is no need for fidelity of information concerning the body states that define an emotion provided the kind of emotion in question can be detected without ambiguity.)
Mirror neurons as 'as-if body' device originated in its body first, and then in the body of someone else:
Mirror neurons are, in effect, the ultimate 'as-if body' device. The mirror-neuron system achieves conceptually what we hypothesized as the 'as-if body loop' system: the simulation, in the brain's body maps, of a body state that is not actually taking place in the organism. The fact that the body state the mirror neurons are simulating is not the subject's does not minimize the power of this functional resemblance. On the contrary, it stands to reason that if a complex brain can simulate someone else's body state, it can simulate one of its own body states. Take, for example, a state that has already occurred in the organism: it should be easier to simulate since it has already been mapped by precisely the same somatosensing structures that are now responsible for simulating it. In fact, we suggest that the as-if system applied to others would not have developed had there not been an as-if system applied to the brain's own organism.
Emotions are 'felt' in our flesh (hence, 'feelings'!):
The as-if body loop, the body loop, and mirror neurons all point to a few remarkable features regarding the perception of the body during the experience of an emotion: The emotion ends up felt in our flesh. The process unfolds in time and is both sensory and motor. The sensing of body changes leads to motor activations that, in turn, can be sensed. All of these steps have the power to evoke related knowledge held in memory.