The Yin and Yang of the Two Brains
Edward F. Block IV, PhD, LAc
September 2009


This work describes the theory of yin/yang in relation to the two brains of the human primate organism (HPO). The basic theory of yin/yang is given and examples of the usage of this method of categorizing phenomena is applied to the central nervous system, the enteric nervous system and the autonomic nervous system components of the sympathetic and parasympathetic divisions. Various aspects of the nervous system of a person are viewed in regard to the characteristic laws of the yin/yang theory in order to show how this method is applied and useful for categorizing the components of a "black box", in this case the nervous components of the human primate organism.


central, nervous, system, enteric, autonomic, yin, yang, theory, human, primate, organism, sympathetic, parasympathetic, balance, phenomena, categorizing, brain


The yin/yang theory is a central and essential concept in the overall schema of traditional Chinese medicine (TCM). All persons involved in the discovery and elucidation of just what comprises beneficial healing intervention in course of the disease process of a human primate organism (HPO) by necessity need to deal with the various aspects of HPO anatomy, physiology and behavioral state. At the time of the development of the cultural components of what is now called Chinese medicine (there are some 53 distinct ethnic groups in contemporary China), one must understand that the knowledge of today concerning microscopic anatomy and cellular physiology was not in evidence. The reason for this is that the concepts originated and became dogma at a time between 5000 years ago and 2000 years ago. Chinese sages took the concepts derived from the observation of the world about them from their everyday living environment and interaction with other people and applied them to the art of medicine. There are 8 branches of TCM and all have at their heart the concept of balance between Yin and Yang forces in the world and within the individual. If balance between those aspects of human life that generate the expression of what are described as a yin and yang state within the person is maintained, that person will remain in a healthy state.

Since the seeker is ever striving to understand the nature of the universe on all levels, just what constitutes, causes and heals disease is but one such study. This work shall expound an interpretation of classical yin/yang theory as applied to the HPO in the aspect of the two brains: the central nervous system and the enteric brain. To do so will require the knowledge and understanding of the person that modern science has provided concerning medical matters. This will involve such contemporary studies as anatomy, microanatomy, gross physiology, cellular physiology, biochemistry and behavior. Also is the idea that is somewhat new to modern medicine and that is that the enteric brain is just as complicated and necessary for life as the central brain. Hopefully, this work will give a different perspective that warrants thinking about and integrating with the rest of the information that we have of the human primate organism for the perspective of TCM.


Yin/Yang Theory and Philosophy

The theory of yin and yang is an integral part of contemporary Chinese culture. Its roots are over 5000 years old. The concept of Yin/Yang is a theoretical method proposed by ancient Chinese sages for observing and analyzing the phenomena of our World. Yin- Yang had been understood for many centuries, but was systematically elaborated and written down by Tsou Yen of the Yin-Yang (Naturalist) School in the Warring States Period (476-221 BCE). Yin and yang combine in a complementary manner and form a method for explaining relationships between objects. Gradually, this logic was developed into a system of thought that was applied to other areas. Yin and yang represent a continuum between two polar opposites, as well as different and opposing aspects within any same phenomenon. The original concept of yin and yang came from the observation of nature and the environment. "Yin" originally referred to the shady side of a mountain slope while "yang" referred to the sunny side of the mountain slope. Later, this thinking was used in understanding other occurrences, which occurred in pairs and had complementary and opposing characteristics in nature. One must realize that this theory is but a means of categorizing phenomena and nothing is intrinsically yin or yang but has qualities attributed to each.

Some examples of these complementary pairs include: sky and earth, day and night, water and fire, active and passive, male and female, etc. Working with these ideas, the ancient sages recognized nearly all things could have yin and yang properties. Yin and yang can describe two relative aspects of the same phenomena such as the example of the slope, or they can describe two different objects like sky and earth.

Yang is usually associated with energetic qualities. For example, movement (outward and upward direction), heat, brightness, expansion, stimulation, activity and excitement are all yang qualities. Yin, in contrast, is associated with the material form of an object and has less energetic qualities such as rest, inward and downward direction, cold, darkness, condensation, inhibition, and nourishment.

The theory characterizes the following aspects:

  1. The Opposition of Yin and Yang
  2. The Interdependence of Yin and Yang
  3. The Inter-Consuming-Supporting Relationship of Yin and Yang
  4. The Inter-Transforming Relationship of Yin and Yang
  5. The Infinite Divisibility of Yin and Yang

Yin and Yang are opposite Pairs

They are either on the opposite ends of a cycle, like the seasons of the year, or, opposites on a linear continuum of energy or matter. This opposition is relative, and can only be spoken of in terms of relationships. For example: Water is Yin relative to steam but Yang in relation to ice. Yin and Yang are never static but in a constant interchanging balance.

Interdependent: can not exist without the other

The Tai Ji (Supreme Ultimate) diagram shows the relationship of Yin & Yang and illustrates interdependence of Yin & Yang.

Nothing is said to be totally Yin or totally Yang. Just as a state of total Yin is reached, Yang begins to grow. Conversely, yin contains the seed of Yang and vice versa. Yin and yang are constantly transforming into each other. For Example: no energy without matter, and no day without night. The Chinese classics state: "Yin creates Yang and Yang activates Yin".

Mutual consumption and inter-transforming function of Yin and Yang

The relative levels of Yin and Yang are continuously changing. Normally this is a harmonious and gradual change, but when either Yin or Yang is out of balance they affect each other, and too much of one can eventually weaken (consume) the other. There are 4 possible states of imbalance.

  1. Preponderance (Excess) of Yin
  2. Preponderance (Excess) of Yang
  3. Weakness (Deficiency) of Yin
  4. Weakness (Deficiency) of Yang

A Brief description of the 2 "Brains" of the HPO in relation to Yin/Yang

Contemporary medical science has shown that each person has 2 distinct but interconnected brains (connected directly by the vagus nerve). One brain is located in the skull cavity and vertebral column and is called the central nervous system (CNS). The other brain is located within and surrounding the alimentary tract in its entirety and is called the enteric nervous system (ENS). The total number of neurons is similar in each brain. The gross anatomy and supporting structures are somewhat different in each. The types of neurotransmitters in each are virtually the same but the distribution and interconnectedness of neurons are not. Both brains produce the same cytokines and thus communicate with the immune system and other neurons via the blood-vascular system if not directly connected by a nerve axon.

Additionally, the entire nervous system is arbitrarily divided into the central (CNS) and peripheral (peripheral nervous system - PNS) segments. Thus, classically in western medical science the CNS is the central portion and the ENS is part of the peripheral portion. All nervous systems have an input and output component. Neurons receive input from other neurons via dendrites at the cell body and in turn transmit output via the axon at the synaptic terminal. This is the derivation of the terms pre-synaptic and post-synaptic. The axon terminal is pre-synaptic and the dendrite terminal is post-synaptic. Additionally neurons receive input from the interstitial fluid in the form of nutritional factors, cytokines, hormones and the like. The effect of these compounds may be located anywhere on the neuron cell membrane surface and not just at the synapse.

The CNS is composed of the brain and spinal cord. Please refer to these websites for a detailed explanation as reference A. The CNS has peripheral neuronal, inter-neuronal and direct neuronal input. Much of what constitutes beingness deals with the conscious and the subconscious. Consciousness resides in the cerebrum while the subconscious is the realm of the thalamus, the basal ganglia, cerebellum and pons/medulla oblongata. The input section of the cerebrum is called the sensory cortex and is located in the left and right parietal and occipital sections. The voluntary output section of the cerebrum is called the motor cortex and is located in the left and right frontal lobes. The sensory sections are considered yin and the motor sections yang. For most persons, consciousness resides in the left-brain cerebral hemisphere and is considered yang. The right-brain cerebral hemisphere and the rest of the brain is considered yin. Since the CNS deals with action and the ENS (please see the following websites as reference B.) with digestion and waste elimination, the CNS is yang and the ENS is yin. This shows the concept of yin within yang (and vice versa) and the infinite divisibility of yin/yang. Likewise, the nervous elements (neurons) of the nervous systems are considered yang while the neuro-endocrine (neurons that secrete hormonal releasing compounds) elements and other blood born elements (hormones and cytokines) are considered yin.

The PNS is composed of elements of the ENS, the spinal ganglia and the sensory neurons located in the skin, organs, deep tissues and glands. The nerves are yang and any secreted elements are yin. Thus, the PNS sends input information (yin) to the CNS and the CNS receives this information, decides upon a course of action and sends messages to act upon those inputs in the appropriate manner (yang).

The autonomic nervous system (ANS) is described as that part of the entire nervous system that takes care of controlling and coordinating the various elements of the nervous system in order to maintain balance of all the systems within the body so as to provide the optimum internal environment for cellular life inside the body structure. Thus, the voluntary aspects of the entire nervous system are deemed yang and the involuntary aspects are deemed yin. The ANS controls many visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, urination, and sexual arousal. Whereas most of its actions are involuntary, some, such as breathing, work in tandem with the conscious mind. It is classically divided into two subsystems: the parasympathetic nervous system (yin) and the sympathetic nervous system (yang). Relatively recently, a third subsystem of neurons that have been named 'non-adrenergic and non-cholinergic' neurons (because they use nitric oxide as a neurotransmitter) have been described and found to be integral in autonomic function, particularly in the gut and the lungs. The ENS is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system. For this discussion it is considered independent.

The role of the hypothalamus in the skull mid-brain is key for controlling what is described as homeostasis, however, a more correct term is rheostasis since the body is continuously in flux and actually oscillates about "set points" rather than staying the same. This skull brain function (yang) mediates through biochemical molecules (yin) via the vascular system (yin) or neurons (yang). Many of these hormone-releasing molecules of the hypothalamus stimulate other neurons to secret hormones (yin) or other glands to secret hormones (yin). This gives you another example of the interdependence and divisibility functions of the yin/yang theory.

In relation to the cause and onset of disease, a relative balance needs to be maintained between those aspects of the nervous system that are said to be yang and those that are called yin. Remember that there are no such yin/yang elements and this designation is but a mere construct of man's thinking, organizing and categorizing activity. Any cause that will result in an imbalance will be taken care of by the ANS unless there is a blocking action. Thus, it is the intent of all medicine to release the blockages, help to clean up the waste and debris and to support proper nutrition so that optimum functional status is achieved.

Yang is the realm of the heavens and yin is the realm of the Earth. This shows us that the CNS is attuned to the flux of electromagnetic energies arising from the solar system. Conversely, the ENS is attuned to the changes in the geomagnetic flux of the Earth. Yang is all about change and Yin is all about resistance to change. For the most part, the fluctuations of the geomagnetic fields and energies of the Earth are quite regular and rhythmic. There are fluctuations due to inconsistencies in the crust of the earth due to underground magma and water flows but these are transient and become relatively stable. The fluctuations of electromagnetic energies of the solar system are both of a steady nature due to orbital mechanics but also of a fluctuating nature due to the volatility of the processes going on within Sol. Also, the Earth receives electromagnetic flux from the galaxy and universe at large. The atmosphere and the earthly dynamo of the core that produces the geomagnetism protect us from all but the most energetic particles. Light energy impinges upon us constantly. Light is yang and particles are yin. Thus, the ENS is tuned to the Earth and the CNS is tuned to the Stars.


The body and consciousness of man subjected to and analyzed by the theory of yin/yang may be categorized ad infinitum. This tool is but one means of deriving both knowledge and understanding of human affairs. The plant kingdom is yin to the animal kingdom yang. Light is yang to the yin of substance. The skull brain is yang to the gut brain yin. Understanding this concept of yin/yang may be applied to maintaining the health of the individual. It is but for us as people to learn to trust our bodies as it teaches us the ways of balance in life and effort.






Oriental Section