This is a paper I wrote for the introductory psychology class I am taking this semester at CCV. The research I did for the paper actually began about 8 months ago when I took a weekend course on the endocrine system with Amy Mathews at The Breathing Project in Manhattan. That weekend sparked my interest in the neuroendocrine system, and that interest has persisted and continues to inform my take on body-mind communication. In case this topic also interests you and you want to read more I have included my references. Let me know what you think!

The Mind Is What the Body Does:
The Neuroendocrine System, The Gut and the Perils of Reductionism

In early 17th century France the philosopher René Descartes, forefather of modern western medicine, made a deal with Rome; in exchange for papal permission to dissect and study human cadavers he agreed that any discoveries he and his fellow men of science made in this pursuit would be purely physical in nature and have no bearing on the mind, the soul, or the emotions, all of which he acknowledged as the exclusive territory of the church. It was thus that dualism was born and its major tenant, the supposition that the mind and the body are made of essentially different substances, one spiritual and one material, was cemented into the foundation of western science. The assumptions of dualism persist in affecting the tone of scientific thought and mainstream medical beliefs to this day (Pert, 1997). Dualistic and reductionist notions are at the heart of popular western understandings of human health and wellness, but these dichotomous concepts are simply unsupported by an overwhelming tide of scientific evidence that the mind is not only what the brain does, but what the body does as a whole.

The Neuroendocrine System and Body-Wide Communication

Prevailing popular views of the mind-body connection assumes that the brain, the mind, and consciousness, which all reside in the human head, function as a sort of “supreme commander” that controls, operates, and rides around in the body, while the body itself is akin to a sort of fleshy automobile. The mind is seen as one’s “Self”, while the body is just a vehicle for that self. This assumption is illustrated perfectly by a conversation the author of this paper had with a neighbor several years ago. This gentleman, let us call him Bob, suffered from Multiple Sclerosis, a debilitating autoimmune disorder in which immune cells attack and destroy the insulating myelin sheaths that incase nerves and thus decrease the capacity of the nervous system to perform its vital task of conducting information throughout the body. When told an anecdote about another acquaintance of the author who was able to manage and eventually eliminate the symptoms of his own MS using the practices of yoga, Bob gave an emphatic and incredulous “That’s not possible.” When questioned as to why he felt so certain, Bob responded, “How can exercise possibly affect my condition? The MS stems from a problem in my brain, isn’t the body is just a biological robot operated by the brain?” What is particularly surprising about this sort of dualistic and reductionist thinking is that it is not only at the heart of popular assumptions about the mind and the body, but also scientific ones (Pert, 1997).

In the introductory chapters of her book Molecules of Emotion, Dr. Candace B. Pert (1997) outlines the slow evolution of modern western science’s understanding of mind-body communication. She explains that until the early part of the 20th century the nervous system was generally thought to be an exclusively electrical mechanism of communication between the brain and the body. Command signals were thought to be generated in the brain and sent to the muscles and organs of the body, while sensory signals generated in the organs were sent back to the brain for analysis and interpretation. Pert (1997) points out that this understanding is highly oversimplified and inaccurate, and yet it is still to this day a popular perception of how the mind and body communicate with one another.

In 1921 the discovery of the first ligand, a neurotransmitter called acetylcholine, marked the humble beginnings of what is still a hot topic of scientific research at the cutting edge of modern medicine; the chemical component of body-wide communication that is at the heart of the nervous and endocrine systems. (Pert, 1997) By the late 1980’s the full significance of chemicals like acetylcholine had begun to come into focus. The work of neuroscientists and endocrinologists had by this time established three important categories of chemical communicators, or ligands. According to Pert (1997), the name “ligand” is a general term for any informational molecule generated in the body that can travel through the blood and cerebral spinal fluid and bind selectively to specific receptors on cells in the brain, the liver, the bones, or anywhere else where such receptor sites exist. Neurotransmitters, the first typoe of ligand discovered, are made of amino acids and were initially believed to be manufactured only in the brain. The primary function of a neurotransmitter is the transmission of chemical information from neuron to neuron across the synaptic gap. A second category of ligand belongs to steroids; these molecules, examples of which include estrogen, testosterone, and cortisol, are made of cholesterol and are thought to be manufactured largely in glands such as the ovaries and the kidneys. The third and final category of ligand is made up of a group of chemicals called peptides. Peptides are made of amino acids and are manufactured in a wide range of locations throughout the body including glands, the digestive tract, and the bones. Peptides are truly “last but not least” in that they make up around 95% of all ligands that have currently been identified in the human body. (Pert, 1997)

Pert (1997) explains that ligands represent just one half of the body’s chemical communication equation, the other half is comprised of the receptor sites for these ligands. The cell membrane of every cell in your body contains several hundred thousand receptor molecules, and each one of these is encoded to match a particular ligand in a sort of biological “lock and key” system that creates specificity as to what sorts of chemical messages can be received where. (Pert 1997) The ligands and their receptors represent a body-wide system of complex and interconnected communication between cells in the brain, organs, glands, bones and tissue that has been dubbed the “neuroendocrine” system (Pert, 1997).

According to Pert (1997), current research has identified over 100 different types of ligand communicator molecules and located at least some of their receptor sites throughout the body, however, despite its vital significance in all bodily processes the neuroendocrine system is still poorly understood. Less than half of all known ductless glandular tissue in the body (typically classified as part of the endocrine system) has been named and scientists do not yet know what kinds of chemicals these tissues produce, where the chemicals are received, or what kinds of messages about cellular behavior they deliver when they get there. Pert (1997) explains that it is likely in the coming years hundreds more ligands and their receptors will be isolated, described, and given names (Pert, 1997).

In contrast to popular reductionist “top down”, brain-centric concepts of how the “mind controls the body”, the behavior of ligands in the neuroendocrine system is complex, far-reaching, and just as often “from the bottom up.” Chemicals manufactured in one location in the body can enter the body fluid and travel to a diverse number of receptor cells in wide ranging locations, delivering information that changes the way those cells are behaving. For example, insulin, a peptide produced in the pancreas, is an important body-wide communicator about the amount of glucose present in the blood with known receptor sites in the liver, skeletal muscle, fat tissue and bones. In the case of insulin, Lee et. al. (2007) have shown that the skeletal system, once considered to be a passive receiver of insulin-born messages about bone density, plays an active role in insulin regulation via a peptide it produces called osteocalcin. For this reason the skeletal system, once conceived to be a relatively “inanimate” rigid structure with the simple function of maintaining the body’s shape, been recommended for reclassification as part of the neuroendocrine system. Oury et. al. (2013) have also recently document osteocalcin’s effects on metabolism, sex-hormone production, and its capacity to bind to neurons in the brains of lab mice where it enhances memory and prevents anxiety and depression. Pert (1997) describes hormones as another example of wide ranging chemical communication via which the body creates the experiences of the mind. Estrogen, which is produced in the sex glands, has receptor sites in uterine tissue, breast tissue, bone, and also the brain where it delivers information about cellular growth, and sexual identity (Pert, 1997).

A Closer Look at the Gut

One of the most fascinatingly self-actuated players in the neuroendocrine system is the gut. The gut is comprised of the esophagus, the stomach, the large and small insestines and the colon, and the study of its complex relationship with the brain is called neurogastronenterology. According to Dr. Michael Gershon (1998) the body’s nervous system is commonly broken down into two components; the central nervous system (composed of nerve cells in the brain and spinal cord) and the peripheral nervous system (nerve cells in the rest of the body), but there is functionally a third nervous system, the enteric nervous system, which is composed of hundreds of millions of nerve cells and is intrinsic to the gut (Gershon, 1998). The enteric nervous system, which evolved long before the central nervous system, is capable of functioning completely independent of input from the brain or spinal cord. Every variety of neurotransmitter that has so far been found in the brain has also been found in the gut, and many chemicals that were once thought to be produced exclusively by the brain are now better understood to be products of both the brain and the digestive tract. As an example, over 95% the body’s serotonin, an important mood and sleep regulating ligand, is produced in the bowel (Gershon, 1998). In fact, with more nerve cells located in the gut than in the spine, the enteric nervous system is so self regulated and produces so many chemicals effecting overall behavior that Gershon (1998) went so far as to title his book on the subject The Second Brain.

Conclusions

British philosopher Thomas Hobbes, a contemporary of Descartes, did not agree with the claims of dualism and proposed that the mind is not a fundamentally different substance than the body but is simply what the brain does (Schacter, Gilbert & Wegner, 2011). This insight was apt at the time, but in light of modern discoveries in the fields of neuroendocrinology and neurogastronenterology, its language is clearly reductionist and over emphasizes the role of the brain. The mind, our inner, subjective experience of ourselves and the world around us, is the product of what the body does as a whole. Our subjective experience of the world, our emotional experiences, our thoughts and perceptions are not created by simple isolated electrical impulses within the autonomous containers of our brains. These experiences arise from a complex web of electro-chemical interactions amongst all of the body’s parts. The body is not like a car or a robot, it is not a system of discrete parts functioning in relative isolation from one another while the brain mans the driver’s seat. The body is more like an ocean, it is vastly complex, rich in nested systems of interrelationship, and its fluid nature lends itself to comingling not to segregation. As western medicine has advanced the more myopic its focus on lone symptoms rather than far reaching causes has become. When we perceive our mental and physical lives as the product of individual parts acting independently rather than as the result of the body’s unified condition in which all parts are informed by their interconnection to one another we run the risk of curing lone symptoms at the cost of damaging the quality of our lives as a whole.

References:

Gershon, M. D. (1998). The Second Brain: A groundbreaking new understanding of nervous disorders of the stomach and intestine. New York: HaeperCollins Publishers.

Lee, N. K., Sowa, H., Hinoi, E., Ferron, M. M. A., Jong, D., Confavreaux, C., … Karsenty, G. (2007). Endocrine Regulation of Energy Metabolism by Skeleton. Cell, 130, 456-469.

Oury, F., Khrimian, L., Denny, C. A., Gardin, A., Chamouni, A., Goeden, N., … Karsenty, G. (2013). Maternal and Offspring Pools of Osteocalcin Influence Brain Development and Functions. Cell, 155, 228-241.

Pert, C. B. (1997) Molecules of Emption: Why you feel the way you feel. New York: Scribner.