Self Comes to Mind

about the state of a good part of the body’s interior—the state of the visceral-chemical body components beneath the skin’s outer perimeter.
    Complementing the complex mapping of the interior sense described above, to which we refer as interoception , are the body-to-brain channels that map the state of skeletal muscles engaged in movement, which are a part of exteroception . Messages from the skeletal muscles use different and fast-conducting kinds of nerve fibers—Aα and Aγ fibers—as well as different stations of the central nervous system all the way into the higher levels of the brain. The upshot of all this signaling is a multidimensional picture of the body in the brain and, thus, in the mind. 6
Representing Quantities and Constructing Qualities
     
    The body-to-brain signaling I have described does not deal merely with the representation of quantities of certain molecules or degrees of smooth muscle contraction. To be sure, the body-to-brain channels do transmit information regarding quantities (how much CO 2 or O 2 is present; how much sugar is in the blood; and so forth). But there is, side by side, a qualitative aspect to the results of the transmission. The state of the body is felt to be in some variation of pleasure or pain, of relaxation or tension: there can be a sense of energy or lassitude, of physical lightness or heaviness; of unimpeded flow or resistance, of enthusiasm or discouragement. How can this qualitative background effect be achieved? To begin with, by arranging the varied quantitative signals arriving in brain-stem structures and in insular cortices so as to compose diverse landscapes for the ongoing body events.

     
Figure 4.1 : Schematics of key brain-stem nuclei involved in life regulation (homeostasis). Three brain-stem levels are marked in descending order (midbrain, pons, and medulla); the hypothalamus (which is a functional component of the brain stem even if it is, anatomically, a part of the diencephalon) is also included. Signaling to and from the body proper and to and from the cerebral cortex is indicated by vertical arrows. Only the basic interconnections are depicted, and only the main nuclei involved in homeostasis are included. The classic reticular nuclei are not included, nor are the monoaminergic and cholinergic nuclei.
The brain stem is often considered a mere conduit for signals from body to brain and brain to body, but the reality is different. Structures such as the NTS (nucleus tractus solitarius) and PBN (parabrachial nucleus) do transmit signals, from body to brain but not passively. These nuclei, whose topographic organization is a precursor of that of the cerebral cortex, respond to body signals, thereby regulating metabolism and guarding the integrity of body tissues. Moreover, their rich, recursive interactions (signified by mutual arrows) suggest that in the process of regulating life, new patterns of signals can be created. The PAG (periaqueductal gray), a generator of complex chemical and motor responses aimed at the body (such as the responses involved in reacting to pain and in the emotions), is also recursively connected to the PBN and the NTS. The PAG is a pivotal link in the body-to-brain resonant loop.
It is reasonable to hypothesize that in the process of regulating life the networks formed by these nuclei also give rise to composite neural states. The word feelings describes the mental aspect of those states.
    To grasp what I have in mind, I ask the reader to imagine a state of pleasure (or anguish) and try to itemize its components by making a brief inventory of the varied parts of the body that are changed in the process: endocrine, cardiac, circulatory, respiratory, intestinal, epidermic, muscular. Now consider that the feeling you will experience is the integrated perception of all such changes as they occur in the landscape of the body. As an exercise, you can actually try to compose the feeling and assign values of intensity to each component. For each instance that you imagine, you will obtain a different quality.
    But there are other ways of constructing qualities. First, as noted earlier, a significant portion of body signals undergoes additional treatment within certain nuclei of the central nervous system. In other words, the signals are processed at intermediate stages, which are not mere relay stations. The machinery of emotion located in the nuclei of the periaqueductal gray is likely to influence processing of body