A new study published in the April, 2023 Nature medical journal reveals the discovery of three unknown areas of the sensory motor cortex in the brain. These areas may be key to understanding mysteries of the body-mind connection. The study shows that parts of the brain area that control movement are plugged into networks involved in thinking and planning, and in control of involuntary bodily functions such as blood pressure and heartbeat. This was a large study, comprising data from nearly 50,000 individuals. Further, the findings were placed in inter-species (macaques vs. humans), clinical (postpartum stroke), and developmental (neonatal, infantile, childhood, and adulthood periods) contexts, utilizing precision functional mapping (PFM) information.
Importance of the Sensory Motor System in Somatics
In the Body of Life, Thomas Hanna explains, “the arrangement of nerve cells in the motor tracts of the cortex represents the human body from bottom to top. It is as if a little man were sketched out along these tracts, and for this reason it has come to be called the sensory homunculus and the motor homunculus”
What is the Homunculus?
The word homunculus is Latin for little man or little person. Thomas Hanna explains, “If we were to run a lightly charged filament across this neuronal keyboard, the muscles and senses would be activated in a rational, sequential manner. There would be a rising contraction of the muscles and an ascending arpeggio of sensations. It is a most rational arrangement, as orderly in its layout as are the ascending keys on a piano keyboard. In fact, it is quite similar. Just as pressing down on the white key of middle C activates the striking of the C string in the piano, so does stimulation of a neuron in these tracts activate the corresponding muscle cell or sensory cell in the body.
Upon looking closer at the ‘little man’, we begin to notice some unusual features of this neural body. The first and perhaps most obvious feature is the enormous space allotted to the hands and face and the small amount allotted to the legs and trunk of the body. Although the legs and trunk are a major portion of the bodily structure, they are a minor portion of the neural structure-a fact that puts us in a better position to judge which bodily functions are the most significant from a neural point of view. In viewing the homunculus, we are, to a large extent, viewing the functional human being as contrasted with the structural human being; in a rather exact sense, we are getting nearer to what the living human body is like: the human soma.
3-D rendition of the old homunculus map
The sensorimotor homunculus is a creature made for perception and action. It is designed for the process of sensate movement. But what we see is not the whole sensorimotor system, merely its highly instructive cortical surface. The neurons of these tracts descend down to other integrative centers that lie just beneath the layer of the cortex and that relate the functions of these tracts to the sensory association area and the premotor association area. Sensory awareness of the inner kinesthetic and proprioceptive feedback of our neural system predisposes the muscular system to adjust itself to more efficient functioning” (Excerpt from the Body of Life)
Comparison of the old homunculus map with the integrate-isolate model
New Research Regarding the Homunculus
The recent research findings published in Nature found that instead of a continuous head-to-toe representation of body movements in a single homunculus, this neural representation of the body is sliced into three sections, one for the feet, another for the hands, and a third for the mouth (see figure above). In the integrate–isolate model, the regions for foot, hand, and mouth fine motor skills are organized somatotopically as three concentric functional zones with distal parts of the effector (toes, fingers and tongue) at the center and proximal ones (knee, shoulder and larynx) on the perimeter. In addition to these, there are three mysterious areas within the homunculus whose significance was not understood. Historically, while these areas had been observed before, scientists considered them not significant since stimulations to these areas did not elicit body movement. Based on fMRI data, scientists argue that these areas, referred to as inner-effector regions in the primary motor cortex, play a role in whole-body action planning, rather than corresponding to single body parts. These areas are thought to have an important role in executing complex movements and regulating internal organs and appear important to the activation of the mid-section (somatic center) of the body. In addition, these action-body regions can become active when someone is only imagining making movements. The most interesting finding is that these inter-effector regions are functionally connected to multiple regions of the cingulo-opercular network (CON), which is critical for physiological control, arousal, and pain. This relationship in particular may be the missing link to the connection between body and mind.
The somato-cognitive action network integrates body control (motor and autonomic) and action planning. This system may have first developed in humans to regulate complex motor skills such as coordinating breathing for speech, and integrating hand, body, and eye movement for tool use. The network appears to be used today in pre-action anticipatory postural, breathing, cardiovascular and arousal changes such as shoulder tension, increased heart rate, or physical nervousness and excitement such as ‘butterflies in the stomach’.
Mind-body Connection
In the Body of Life Thomas Hanna explains, “the entire brain of an adult male weighs something in the neighborhood of fifty ounces-or about fourteen hundred grams. The brain is a colossal organ. It is an aggregate of some twelve billion neurons, most of which (nine billion) are concentrated in the top layer, the cerebral cortex. In the center of these nerve cells, like the main pole of a tent upon which all else hangs, stands the sensorimotor system. This massive assemblage of nerve cells is united in performing one dual function: moving the body in coordination and integrating the sensory information that it receives from the body”
The three colored spots on each hemisphere of the motor cortex in the brain, shown above, do not affect movement directly but connect to areas involved in thinking, planning, control of basic bodily functions and to more complex combinations of both fine and gross motor movement.
Researchers believe these areas may have evolved from a simpler system meant to integrate movement with physiology so that, for instance, we don’t pass out when we stand up. The system then became more complex as we needed to do increasingly complicated motor related planning for difficult human tasks.
In the Nature article, scientists explain, while it was already known that the sensory motor cortex was essential for moving muscles of the body, other unexplained phenomena, such as, why anxiety makes people want to pace back and forth; why stimulating the Vagus nerve, which regulates internal organ functions such as digestion and heart rate, may alleviate depression; or why people who exercise regularly report a more positive outlook on life, these have all remained a scientific mystery. The research findings by these scientists, however, may explain these body-mind connections once and for all.
Somato-Cognitive Action Network (SCAN). This network is used for integrating goals, regulating physiology, and planning complex body movement.
So, what do these new scientific findings about the homunculus mean for the future of Somatic Education? The findings validate and explain how mind and body states interact with each other and add legitimacy to the subjective somatic experience as being central to voluntary control of sensory motor movement. The parasympathetic and sympathetic nervous systems are in direct communication and linked to higher level, voluntary cognitive functions in the cortex. The 1st person perspective of somatic experience, once thought of as quite separate from the 3rd person view of medical science, may now share a new paradigm together in the furtherance of the elimination of chronic pain and suffering. Further research is needed, of course, but somatic educators can look forward to fresh scientific validation of what has always been known as true. The body-mind connection is real.
References
Gordon, E. M., Chauvin, R. J., Van, A. N., Rajesh, A., Nielsen, A., Newbold, D. J., ... & Dosenbach, N. U. (2023). A somato-cognitive action network alternates with effector regions in motor cortex. Nature, 1-9.
Hanna, Thomas. The body of life: Creating new pathways for sensory awareness and fluid movement. Healing Arts Press, Rochester, Vermont, 1993.