Self Comes to Mind

confined to viscera—our gut and our bronchi contract and distend thanks to smooth muscles. The walls of our arteries are made in good part of smooth muscles—one’s blood pressure rises when they tighten their grip around the artery. Striated muscles, by contrast, are attached to bones in the skeleton and produce external body movement. The only exception to this scheme of things is the heart, which is also made of striated muscle fibers and whose contractions serve not body movement but rather the pumping of blood. Signals describing the state of the heart are sent to brain sites dedicated to the viscera, not to those that pertain to movement.
    When skeletal muscles are connected to two bones articulated by a joint, the shortening of their fibers generates movement. Picking up an object, walking, talking, breathing, and eating are all actions that depend on the contraction and distension of skeletal muscles. Whenever those contractions occur, the configuration of the body changes. Except for moments of complete immobility, which are infrequent in the awake state, the configuration of the body in space changes continuously, and the map of the body represented in the brain changes accordingly.
    In order to control movement with precision, the body must instantly convey to the brain information on the state of skeletal muscle contraction. This requires efficient nerve pathways, which are evolutionarily more modern than those that convey signals from the viscera and internal milieu. These pathways arrive in brain regions dedicated to sensing the state of these muscles.
    As noted, the brain also sends messages to the body. In fact, many aspects of the body states being continuously mapped in the brain were caused in the first place by brain signals to the body. As in the case of communication from the body to the brain, the brain talks to the body via both neural and chemical channels. The neural channel uses nerves, whose messages lead to the contraction of muscles and the execution of actions. The chemical channels involve hormones, such as cortisol, testosterone, and estrogen. The release of hormones changes the internal milieu and the operation of the viscera.
    Body and brain are engaged in a continuous interactive dance. Thoughts implemented in the brain can induce emotional states that are implemented in the body, while the body can change the brain’s landscape and thus the substrate for thoughts. The brain states, which correspond to certain mental states, cause particular body states to occur; body states are then mapped in the brain and incorporated into the ongoing mental states. A small alteration on the brain side of the system can have major consequences for the body state (think of the release of any hormone); likewise, a small change on the body side (think of a broken tooth filling) can have a major effect on the mind once the change is mapped and perceived as acute pain.
From Body to Brain
     
    The remarkable European school of physiology that flourished from the middle of the nineteenth century to the early twentieth described the contours of body-to-brain signaling with admirable accuracy, but the relevance of this general scheme for the understanding of the mind-body problem went unnoticed. The neuroanatomical and neurophysiological details, not surprisingly, have been uncovered only in the past few years. 5
    The state of the body’s interior is conveyed to the brain via dedicated neural channels to specific brain regions. Special nerve-fiber types (Aδ and C fibers) bring signals from every nook and cranny of the body into selected parts of the central nervous system (such as the lamina-I section of the posterior horn of the spinal cord), at every level of the vertical spinal cord length, and the pars caudalis of the trigeminal nerve. The spinal cord components handle signals from the internal milieu and viscera of the body except the head—the chest, abdomen, and limbs. The trigeminal nerve nucleus handles signals from the internal milieu and viscera of the head, including the face and its skin, the scalp, and the paramount pain-generating meningeal membrane, the dura mater. Equally dedicated are the brain regions charged with handling the signals after they enter the central nervous system and as subsequent signals march toward the higher levels of the brain.
    The least one can say is that along with chemical information available in the bloodstream, these neural messages inform the brain