This essay is my humble, but serious, contribution towards identifying the steps necessary to resolve the apparently unbridgeable gap between the physics of the external world and the physics of the internal world of our minds. This gap, known as dualism, was formalised in the 1600s by Descartes, separating the objective world (res extensa) from the subjective world (res cogitans). It represents the fundamental, hitherto unexplained gap between neuroscience and phenomenology.
I will argue that is possible to bring these distinct domains under the single conceptual umbrella of physics. It is possible to see the mind as a part of nature, by binding these domains into one, where all phenomena are identified by their four-dimensional coordinates in time and space. This step is a necessary and sufficient condition for testing their physical existence and consequent scientific analysis. In other words, anything that exists must have four-dimensional coordinates.
Therefore, the question is not whether mental and cultural phenomena are physical, but rather, how can they be appropriately described and studied as four-dimensional structures.
I propose to extend a physical conceptual frame within the Newtonian-Einsteinian Universe to be suitable to include subjective experience. This approach will also bring a unified view of what we should regard as reality, arising from the immediate direct experience of the here and now to the broader indirect knowledge of what lies beyond direct experience. I will argue that some philosophical choices are dead-ends. Indeed, only a few choices lead, with careful navigation, to progress in this quest for a unified realm of Physics that encompasses humans themselves. Therefore I will begin by describing some of the principles of Physics that could be applied to bridge the gap between objective and subjective knowledge.
I will take the simple but widely accepted view that the substrate of mental activity is the neural activity of the brain. At a fundamental level, the nervous system consists of interconnected nerve cells, organised as a neuromechanical loop with sensory neurons connecting via interneurons to motor neurons. The brain, including the cerebral cortex, evolved as a hierarchical structure with superimposed internal neural loops increasingly distant from the external world. These internal loops are the substrate of all mental states from the automatic and subconscious to the all the extraordinary levels of conscious experience. Nothing can enter the inner world of the nervous system except via its sensory inputs. All actions, no matter where they are initiated within the massively interconnected internal loops of the nervous system, can only emerge via motor neurons.
The appearance of a nervous system enabled organisms to interact flexibly with their environment and provided greater autonomy in their behaviour. The physical bases of brain functions are electrochemical processes which generate extremely complex patterns of activity. Mapping such patterns of neural activity in time and space is equivalent to identifying the four-dimensional physical structures underlying brain processes. The four-dimensional structures of specific patterns of neural activity in time and space are the proper bases of any inner mental state including conscious experiences. We live in a four-dimensional world which we can only ever experience in the present moment, that short time in which we can act and react.
I will emphasise that all experiences of external or internal phenomena alike are ‘subjective’, constructed by the brain of each of us. To make any experience ‘objective’, it must be shared with other individuals, and this can happen only with congeners endowed with similar neural processes. The neural processes underlying shared experiences are crucial to understanding the nature and validity of any reality. As the number of levels of superimposed internal loops increases, so the horizon of existential experience broadens. Testing the validity of individual and collective shared experiences of new horizons is crucial for the ability of our species to adapt to an ever-changing environment.
The success of the experimental science is the best evidence of this validation process. In parallel, the tremendous creative power of human imagination represents a unique feature of the human brain, built up from a complex hierarchy of internal neural loops. The pleasure we experience from arts and music represents the most pure expression of the operation of these internal neural loops. On the other hands, myths, religious cosmologies, and absolute ideologies represent imagination unconstrained by any test of reality and are most dangerous traps of our otherwise wonderful imagination.
Why did I write it?
This essay represents a life-long journey of my thinking accrued through my long career in teaching and research. My desire of reconciling the apparent separate worlds of mind and matter, placing both within a single ‘physical’ perspective, grew slowly since I was a teenager in search of an explanation for the unique features of the human mind. This is the main reason why I choose to study Medicine. I argued that if I wanted to deal with the human brain, I needed to have appropriate professional credentials. Although I never intended to practice Medicine, I had sufficient experience of part time work as general practitioner to point me in the direction of studies of the nervous system1.
I have taught generations of medical and science students from 1975, soon after the opening in 1974 of the Medical School at Flinders University in Adelaide, Australia. As a foundation lecturer in Physiology, I had been working on the enteric nervous system (ENS) since the mid 1960s, first as a medical student in Turin and then from 1970 as a postdoctoral researcher in the Department of Zoology at Melbourne University, where Professor Geoffrey Burnstock ran a successful multidisciplinary department on many aspects of the autonomic nervous system2. The enteric nervous system of mammals was then a little-known component of the autonomic nervous system controlling the gut. Since then, it has been recognised as a complex system of neural circuits with a high degree of autonomy from the central nervous system (CNS). It includes local sensory inputs (primary afferent neurons), interneurons and motor outputs to target tissues in the gut wall (both excitatory and inhibitory motor neurons).
In 1987, we wrote the first monograph on the organisation and functions of the ENS3. At the time, I was teaching locomotion of vertebrates to students in undergraduate neuroscience courses. The idea that propulsion of intestinal contents is a type of locomotion rather than being a simple reflex, arose by comparing it to the mechanism of actual locomotion in vertebrates. Since then, generations of younger colleagues in my laboratory and around the world have joined the quest to understand how this relatively simple nervous system generates the rich and complex range of motor behaviour that guarantees the appropriate progress of contents along the digestive tube.
Teaching in the new medical school at Flinders University facilitated the integration of diverse disciplines. We taught the medical curriculum according to body systems, and I was the coordinator of the Nervous System program for several decades, teaching collaboratively with Biochemists, Anatomists, Physiologists, Pharmacologists, Immunologists, Neurologists, and Psychiatrists. This compelled me to become familiar with many aspects of the structure and function of the nervous system, with the challenge to give a comprehensive perspective to students, while avoiding excessive artificial separations between disciplines.
Following a symposium in 2008 on the relation between neuroscience and the nature of consciousness and the self, I realised that not only did we not know the neural correlate of how the brain shapes the mind, but we did not even know how the enteric nervous system of the intestine shapes faeces! I like to think that over decades of research I have contributed somehow to answer this humble question. Since my retirement in 2022, I could return to full time writing and completing this essay.
No matter how convincing my perspective might turn out to be, I am fully aware that although human imagination is very powerful, we will find that nature is always much more imaginative than we ever can be. As Hamlet famously said, “There are more things in heaven and earth, Horatio, than are dreams of in your philosophy” (Hamlet Act 1, scene 5, 159–167).
Knowing and understanding are historically long social processes that never will be complete. Let’s move then on tiptoes, expecting traps and surprises at every step. These traps are set mostly by our being embedded in the physical world. Our very existence in a world which we are trying to understand has given rise to endless logical paradoxes and significant moral dilemmas. Rather than trying to look from outside this world, it is perhaps better to accept of being part of it. As Gurdulù, a character created by Italo Calvino says, “he has ingested a pint of water before realising that it is not the sea that has to fit in him but is him that has to fit in the sea”4. I share the common paradoxical feeling of realising that we are simultaneously almost nothing in the universe and yet we, as individuals, are the most important thing in it!
It is about us, as sentient agents, thinking beings, agents in life, who have hopes and fears, who feel deep emotions for the world of nature, for a child’s smile, and who, for better or worse, act in a world that confronts us as an unstoppable flow of the river of life, at times quietly, at times tumultuous, but always running to the very end of our personal existence.
Why should someone read it?
I would like to think that after reading this essay, readers may find some guidance in the complex issues that inform the relations between us and the rest of the world without having to accept historical dualism. Students in science may recognize the centrality of the subjective shared experiences as the basis of knowledge. Students in the humanities may recognize the importance of rendering objective any knowledge by testing reality. This may help to overcome the so-called divide of the ‘two cultures’ proposed by CP Snow. Philosophers may appreciate that without having to become scientists, appropriate aspects of Physics are easily accessible and suitable to deal with the apparent ‘immateriality’ of mental functions. Neuroscientists may appreciate my proposed architecture of the nervous system as a system of superimposed internal neural loops which can be related to the different levels of experiential existence.
There has been an historical shift of the human thinking over the past millennia towards the idea that we cannot give a reliable explanation of the universe without considering our place in it as observers. The very process of knowledge involves an interaction with the world and includes an observer-agent in the description of the world itself and of the ‘self’.
The main challenge then is how to include the observer/experiencer in the description of the world and to overcome the unsettling realisation that whatever is the ultimate nature of the world, we are sentient-thinking beings acting in the very world we are trying to understand. We are both ‘observers and actors’ as already pointed by Kant when he stated, “an organism is both a cause and effect of itself”5
Summary
In this essay I have:
[1] ... accepted a human-centered, neurally-based way to understand, investigate, and comprehend the world by its interaction with the world via sensory-motor neural loops.
[2] ... unified ways to describe phenomena in the world, above the level of quantum mechanics, as 4D spatio-temporal structures of increasing complexity (stratified hierachical universe).
[3] ... summarised the suitable physical concepts that best describe the open nature of the universe, new at every moment.
[4] ... described the physics of active media as suitable tools to investigate the nervous system.
[5] ... ascribed to the brain all phenomena associated with mental functions.
[6] ... proposed that the fundamental architecture of the brain consists of superimposed internal neural loops forming a novel hierarchical system.
[7] ... defined the distance from the external world of the internal loops as the number of synapses from the lowest sensory-motor loop.
[8] ... pointed out that the only interaction with the world occurs at the lowest level of the lower sensory-motor loop.
[9] ... defined a sense of reality, based on the adequacy of behaviour to the actual the environmental conditions.
[10] ... resolved the historical Cartesian dualism by pointing out the transition occurring at the interface between nervous system and the rest of the world, ie, between the physics of the external world and the physics of the internal neural world (electrochemistry).
[11] ... proposed that to be able to understand and analyse the relation between neural activity of the brain and corresponding mental states, it is necessary to record and represent graphically neural activity at the appropriate level as spatio-temporal structures.
[12] ... established that human experience only occur in the present, which can be defined as the time within which an action can occur.
[13] ... concluded that when an action is made, it becomes the past and the experience becomes memory. Before an action happens, it is still in the future can only be experienced as imagination or a plan or desire.
[14] ... maintained that issues of ethics become only an issue of what we do in the present.
[15] ... proposed that as the number of hierarchical levels of neural loops increases, the horizon of existence broadens, increasing the range of possible imaginary events.
[16] ... accepted that all experiences are subjective in principle. They are made objective by sharing experiences using similar neural cognitive processes and have to be brought back to shared sensory experiences.
[17] ... warned that if imagined new worlds cannot fulfil this requirement, they remains dangerous dreams and give rise to beliefs systems, myths, religions, absolutist ideologies, etc, endangering the very survival of humanity.
[18] ... concluded that human imagination and creativity, as explorations both of the external and internal worlds, can be expressed with no absolute ideologies. They can be harmless and totally pleasant in their own way such as in art, music, and sports.
- See my memoir: Adventures in Gut Neuroscience: A Biography. https://marcellocosta.au/wp/memoir-adventures-in-gut-neuroscience/ ↩︎
- See: Nick J Spencer & Marcello Costa (2021): The extraordinary partnership of Geoff Burnstock and Mollie Holman. Autonomic Neuroscience 234: 102831; R. Allan North & Marcello Costa (2021): “Geoffrey Burnstock. 10 May 1929—3 June 2020″. Biographical Memoirs of Fellows of the Royal Society. 71: 37–58, Click here to download the PDF. ↩︎
- John Furness and Marcello Costa (1987): The Enteric Nervous System. Churchill Livingstone. ↩︎
- Italo Calvino (1959/1962): The Non-Existent Knight. ↩︎
- Immanuel Kant (1790): Critique of judgement. Part 2, Critique of teleological judgement. Translated by WS Pluhar, Hackett Publishing Co. ↩︎