Self Comes to Mind

straightforward mapping (for example, the mapping of the position of a limb in space), a substantial part of the signaling is first treated by subcortical nuclei, within the spinal cord and especially in the brain stem, which should not be conceived of as way stations for body signals en route to the cerebral cortex. As we shall see in the next section, something is added at that intermediate stage. This is quite important when it comes to the signals related to the body’s interior that come to constitute feelings. Moreover, aspects of the body’s physical structure and function are engraved in brain circuitry, from early in development, and generate persistent patterns of activity. In other words, some version of the body is permanently re-created in brain activity. The heterogeneity of the body is mimicked in the brain, one of the high marks of the brain’s body-aboutness. Last, the brain can do more than merely map states that are actually occurring, with more or less fidelity: it can also transform body states and, most dramatically, simulate body states that have not yet occurred.
    Those who are unacquainted with neuroscience may assume that the body operates as a single unit, a single lump of flesh connected to the brain by live wires called nerves. The reality is quite different. The body has numerous separate compartments. To be sure, the viscera to which so much attention is paid are essential. The incomplete list of viscera includes the usual suspects: the heart, the lungs, the gut, the liver and pancreas, the mouth, the tongue, and the throat; the endocrine glands (e.g., pituitary, thyroid, adrenals); the ovaries and testes. But the list needs also to include less-usual suspects: an equally vital but less-recognized organ, the skin, which envelops our entire organism; the bone marrow; and two dynamic shows called blood and lymph. All of these compartments are indispensable for the body’s normal operation.
    Perhaps not surprisingly, early human minds, less integrated and sophisticated than ours, easily perceived the broken-down, piecemeal reality of our bodies, as suggested by the words that have come to us from Homer. Iliad humans do not speak of a whole body (soma) but rather of body parts, namely, limbs. Blood and breath and visceral functions are designated by the word psyche , not yet called to duty as “mind” or “soul.” The animation that drives the body, probably mixed with drive and emotion, is the thumos and the phren . 4
    Body-brain communication goes both ways, from body to brain and in reverse. The two ways of communication, however, are hardly symmetrical. The body-to-brain signals, neural and chemical, permit the brain to create and maintain a multimedia documentary on the body, and allow the body to alert the brain to important changes occurring in its structure and state. The internal milieu—the bath that all body cells inhabit and of which the blood chemistries are an expression—also sends 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. So the range of information conveyed to the brain is extremely wide. It includes, for example, the state of contraction or dilation of smooth muscles (the muscles that form, for example, 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. In other words, the brain knows what the past state of the body has been and can be told of modifications occurring in that state. The latter is essential if the brain is to produce corrective responses to changes that threaten life. The brain-to-body signals, on the other hand, neural as well as chemical, consist of commands to change the body. The body tells the brain: this is how I am built and this is how you should see me now. The brain tells the body what to do to maintain its even keel. Whenever it is called for, it also tells the body how to construct an emotional state.
    There is more to the body, however, than internal organs and internal milieu. There are also muscles, and they come in two varieties: smooth and striated. The striated variety shows characteristic “bands” (striae) under the microscope, while the smooth variety does not. Smooth muscles are evolutionarily ancient and are