The mind–body problem is a debate concerning the relationship between thought and consciousness in the human mind, and the brain as part of the physical body. It is distinct from the question of how mind and body function chemically and physiologically, as that question presupposes an interactionist account of mind-body relations. This question arises when mind and body are considered as distinct, based on the premise that the mind and the body are fundamentally different in nature.
The problem was addressed by René Descartes in the 17th century, resulting in Cartesian dualism, and by pre-Aristotelian philosophers, in Avicennian philosophy, and in earlier Asian traditions. A variety of approaches have been proposed. Most are either dualist or monist. Dualism maintains a rigid distinction between the realms of mind and matter. Monism maintains that there is only one unifying reality, substance or essence, in terms of which everything can be explained.
Each of these categories contains numerous variants. The two main forms of dualism are substance dualism, which holds that the mind is formed of a distinct type of substance not governed by the laws of physics, and property dualism, which holds that mental properties involving conscious experience are fundamental properties, alongside the fundamental properties identified by a completed physics. The three main forms of monism are physicalism, which holds that the mind consists of matter organized in a particular way; idealism, which holds that only thought truly exists and matter is merely an illusion; and neutral monism, which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them. Psychophysical parallelism is a third possible alternative regarding the relation between mind and body, between interaction (dualism) and one-sided action (monism).
Several philosophical perspectives have been developed which reject the mind–body dichotomy. The historical materialism of Karl Marx and subsequent writers, itself a form of physicalism, held that consciousness was engendered by the material contingencies of one's environment. An explicit rejection of the dichotomy is found in French structuralism, and is a position that generally characterized post-war Continental philosophy.
The absence of an empirically identifiable meeting point between the non-physical mind (if there is such a thing) and its physical extension (if there is such a thing) has proven problematic to dualism, and many modern philosophers of mind maintain that the mind is not something separate from the body. These approaches have been particularly influential in the sciences, particularly in the fields of sociobiology, computer science, evolutionary psychology, and the neurosciences.
An ancient model of the mind known as the Five-Aggregate Model, described in the Buddhist teachings, explains the mind as continuously changing sense impressions and mental phenomena. Considering this model, it is possible to understand that it is the constantly changing sense impressions and mental phenomena (i.e., the mind) that experiences/analyzes all external phenomena in the world as well as all internal phenomena including the body anatomy, the nervous system as well as the organ brain. This conceptualization leads to two levels of analyses: (i) analyses conducted from a third-person perspective on how the brain works, and (ii) analyzing the moment-to-moment manifestation of an individual's mind-stream (analyses conducted from a first-person perspective). Considering the latter, the manifestation of the mind-stream is described as happening in every person all the time, even in a scientist who analyses various phenomena in the world, including analyzing and hypothesizing about the organ brain.
Philosophers David L. Robb and John F. Heil introduce mental causation in terms of the mind–body problem of interaction:
Mind–body interaction has a central place in our pretheoretic conception of agency. Indeed, mental causation often figures explicitly in formulations of the mind–body problem. Some philosophers insist that the very notion of psychological explanation turns on the intelligibility of mental causation. If your mind and its states, such as your beliefs and desires, were causally isolated from your bodily behavior, then what goes on in your mind could not explain what you do. If psychological explanation goes, so do the closely related notions of agency and moral responsibility. Clearly, a good deal rides on a satisfactory solution to the problem of mental causation [and] there is more than one way in which puzzles about the mind's "causal relevance" to behavior (and to the physical world more generally) can arise.
[René Descartes] set the agenda for subsequent discussions of the mind–body relation. According to Descartes, minds and bodies are distinct kinds of "substance". Bodies, he held, are spatially extended substances, incapable of feeling or thought; minds, in contrast, are unextended, thinking, feeling substances. If minds and bodies are radically different kinds of substance, however, it is not easy to see how they "could" causally interact. Princess Elizabeth of Bohemia puts it forcefully to him in a 1643 letter:
how the human soul can determine the movement of the animal spirits in the body so as to perform voluntary acts—being as it is merely a conscious substance. For the determination of movement seems always to come about from the moving body's being propelled—to depend on the kind of impulse it gets from what sets it in motion, or again, on the nature and shape of this latter thing's surface. Now the first two conditions involve contact, and the third involves that the impelling thing has extension; but you utterly exclude extension from your notion of soul, and contact seems to me incompatible with a thing's being immaterial...
Elizabeth is expressing the prevailing mechanistic view as to how causation of bodies works. Causal relations countenanced by contemporary physics can take several forms, not all of which are of the push–pull variety.— David Robb and John Heil, "Mental Causation" in The Stanford Encyclopedia of Philosophy
In neuroscience, much has been learned about correlations between brain activity and subjective, conscious experiences. Many suggest that neuroscience will ultimately explain consciousness: "...consciousness is a biological process that will eventually be explained in terms of molecular signaling pathways used by interacting populations of nerve cells..." However, this view has been criticized because consciousness has yet to be shown to be a process, and the "hard problem" of relating consciousness directly to brain activity remains elusive.
Cognitive science today gets increasingly interested in the embodiment of human perception, thinking, and action. Abstract information processing models are no longer accepted as satisfactory accounts of the human mind. Interest has shifted to interactions between the material human body and its surroundings and to the way in which such interactions shape the mind. Proponents of this approach have expressed the hope that it will ultimately dissolve the Cartesian divide between the immaterial mind and the material existence of human beings (Damasio, 1994; Gallagher, 2005). A topic that seems particularly promising for providing a bridge across the mind–body cleavage is the study of bodily actions, which are neither reflexive reactions to external stimuli nor indications of mental states, which have only arbitrary relationships to the motor features of the action (e.g., pressing a button for making a choice response). The shape, timing, and effects of such actions are inseparable from their meaning. One might say that they are loaded with mental content, which cannot be appreciated other than by studying their material features. Imitation, communicative gesturing, and tool use are examples of these kinds of actions.— Georg Goldenberg, "How the Mind Moves the Body: Lessons From Apraxia" in Oxford Handbook of Human Action
The neural correlates of consciousness "are the smallest set of brain mechanisms and events sufficient for some specific conscious feeling, as elemental as the color red or as complex as the sensual, mysterious, and primeval sensation evoked when looking at [a] jungle scene..." Neuroscientists use empirical approaches to discover neural correlates of subjective phenomena.
A science of consciousness must explain the exact relationship between subjective conscious mental states and brain states formed by electrochemical interactions in the body, the so-called hard problem of consciousness. Neurobiology studies the connection scientifically, as do neuropsychology and neuropsychiatry. Neurophilosophy is the interdisciplinary study of neuroscience and philosophy of mind. In this pursuit, neurophilosophers, such as Patricia Churchland,  Paul Churchland and Daniel Dennett, have focused primarily on the body rather than the mind. In this context, neuronal correlates may be viewed as causing consciousness, where consciousness can be thought of as an undefined property that depends upon this complex, adaptive, and highly interconnected biological system. However, it's unknown if discovering and characterizing neural correlates may eventually provide a theory of consciousness that can explain the first-person experience of these "systems", and determine whether other systems of equal complexity lack such features.
The massive parallelism of neural networks allows redundant populations of neurons to mediate the same or similar percepts. Nonetheless, it is assumed that every subjective state will have associated neural correlates, which can be manipulated to artificially inhibit or induce the subject's experience of that conscious state. The growing ability of neuroscientists to manipulate neurons using methods from molecular biology in combination with optical tools was achieved by the development of behavioral and organic models that are amenable to large-scale genomic analysis and manipulation. Non-human analysis such as this, in combination with imaging of the human brain, have contributed to a robust and increasingly predictive theoretical framework.
There are two common but distinct dimensions of the term consciousness, one involving arousal and states of consciousness and the other involving content of consciousness and conscious states. To be conscious of something, the brain must be in a relatively high state of arousal (sometimes called vigilance), whether awake or in REM sleep. Brain arousal level fluctuates in a circadian rhythm but these natural cycles may be influenced by lack of sleep, alcohol and other drugs, physical exertion, etc. Arousal can be measured behaviorally by the signal amplitude required to trigger a given reaction (for example, the sound level that causes a subject to turn and look toward the source). High arousal states involve conscious states that feature specific perceptual content, planning and recollection or even fantasy. Clinicians use scoring systems such as the Glasgow Coma Scale to assess the level of arousal in patients with impaired states of consciousness such as the comatose state, the persistent vegetative state, and the minimally conscious state. Here, "state" refers to different amounts of externalized, physical consciousness: ranging from a total absence in coma, persistent vegetative state and general anesthesia, to a fluctuating, minimally conscious state, such as sleep walking and epileptic seizure.
Many nuclei with distinct chemical signatures in the thalamus, midbrain and pons must function for a subject to be in a sufficient state of brain arousal to experience anything at all. These nuclei therefore belong to the enabling factors for consciousness. Conversely it is likely that the specific content of any particular conscious sensation is mediated by particular neurons in the cortex and their associated satellite structures, including the amygdala, thalamus, claustrum and the basal ganglia.
The following is a very brief account of some contributions to the mind–body problem.
The Buddha (480–400 B.C.E), founder of Buddhism, described the mind and the body as depending on each other in a way that two sheaves of reeds were to stand leaning against one another and taught that the world consists of mind and matter which work together, interdependently. Buddhist teachings describe the mind as manifesting from moment to moment, one thought moment at a time as a fast flowing stream. The components that make up the mind are known as the five aggregates (i.e., material form, feelings, perception, volition, and sensory consciousness), which arise and pass away continuously. The arising and passing of these aggregates in the present moment is described as being influenced by five causal laws: biological laws, psychological laws, physical laws, volitional laws, and universal laws. The Buddhist practice of mindfulness involves attending to this constantly changing mind-stream.
Ultimately, the Buddha's philosophy is that both mind and forms are conditionally arising qualities of an ever-changing universe in which, when nirvāna is attained, all phenomenal experience ceases to exist. According to the anattā doctrine of the Buddha, the conceptual self is a mere mental construct of an individual entity and is basically an impermanent illusion, sustained by form, sensation, perception, thought and consciousness. The Buddha argued that mentally clinging to any views will result in delusion and stress, since, according to the Buddha, a real self (conceptual self, being the basis of standpoints and views) cannot be found when the mind has clarity.
Plato (429–347 B.C.E.) believed that the material world is a shadow of a higher reality that consists of concepts he called Forms. According to Plato, objects in our everyday world "participate in" these Forms, which confer identity and meaning to material objects. For example, a circle drawn in the sand would be a circle only because it participates in the concept of an ideal circle that exists somewhere in the world of Forms. He argued that, as the body is from the material world, the soul is from the world of Forms and is thus immortal. He believed the soul was temporarily united with the body and would only be separated at death, when it would return to the world of Forms. Since the soul does not exist in time and space, as the body does, it can access universal truths. For Plato, ideas (or Forms) are the true reality, and are experienced by the soul. The body is for Plato empty in that it can not access the abstract reality of the world; it can only experience shadows. This is determined by Plato's essentially rationalistic epistemology.
It is not necessary to ask whether soul and body are one, just as it is not necessary to ask whether the wax and its shape are one, nor generally whether the matter of each thing and that of which it is the matter are one. For even if one and being are spoken of in several ways, what is properly so spoken of is the actuality.— De Anima ii 1, 412b6–9
In the end, Aristotle saw the relation between soul and body as uncomplicated, in the same way that it is uncomplicated that a cubical shape is a property of a toy building block. The soul is a property exhibited by the body, one among many. Moreover, Aristotle proposed that when the body perishes, so does the soul, just as the shape of a building block disappears with destruction of the block.
In religious philosophy of Eastern monotheism, dualism denotes a binary opposition of an idea that contains two essential parts. The first formal concept of a "mind-body" split may be found in the "divinity - secularity" dualism of the ancient Persian religion of Zoroastrianism around the mid-fifth century BC. Gnosticism is a modern name for a variety of ancient dualistic ideas inspired by Judaism popular in the first and second century AD. These ideas later seem to have been incorporated into Galen's "tripartite soul" that led into both the Christian sentiments  expressed in the later Augustinian theodicy and Avicenna’s Platonism in Islamic Philosophy.
Like Aristotle, St. Thomas Aquinas (1225–1274) believed that the mind and the body are one, like the seal and the wax are one, and it is therefore pointless to ask whether they are one. However, (referring to "mind" as "the soul") he asserted that the soul persists after the death of the body in spite of their unity, calling the soul "this particular thing". Since his view was primarily theological rather than philosophical, it is impossible to fit it neatly within either the category of physicalist or dualist.
My view is that this gland is the principal seat of the soul, and the place in which all our thoughts are formed.— René Descartes, Treatise of Man
[The] mechanism of our body is so constructed that simply by this gland's being moved in any way by the soul or by any other cause, it drives the surrounding spirits towards the pores of the brain, which direct them through the nerves to the muscles; and in this way the gland makes the spirits move the limbs.— René Descartes, Passions of the Soul
His posited relation between mind and body is called Cartesian dualism or substance dualism. He held that mind was distinct from matter, but could influence matter. How such an interaction could be exerted remains a contentious issue.
For Kant (1724–1804) beyond mind and matter there exists a world of a priori forms, which are seen as necessary preconditions for understanding. Some of these forms, space and time being examples, today seem to be pre-programmed in the brain.
...whatever it is that impinges on us from the mind-independent world does not come located in a spatial or a temporal matrix,...The mind has two pure forms of intuition built into it to allow it to... organize this 'manifold of raw intuition'.— Andrew Brook, Kant's view of the mind and consciousness of self: Transcendental aesthetic
Kant views the mind–body interaction as taking place through forces that may be of different kinds for mind and body.
On the epiphenomenalist view, mental events play no causal role. Huxley, who held the view, compared mental events to a steam whistle that contributes nothing to the work of a locomotive.— William Robinson, Epiphenomenalism
For Popper (1902–1994) there are three aspects of the mind–body problem: the worlds of matter, mind, and of the creations of the mind, such as mathematics. In his view, the third-world creations of the mind could be interpreted by the second-world mind and used to affect the first-world of matter. An example might be radio, an example of the interpretation of the third-world (Maxwell's electromagnetic theory) by the second-world mind to suggest modifications of the external first world.
The body–mind problem is the question of whether and how our thought processes in World 2 are bound up with brain events in World 1. ...I would argue that the first and oldest of these attempted solutions is the only one that deserves to be taken seriously [namely]: World 2 and World 1 interact, so that when someone reads a book or listens to a lecture, brain events occur that act upon the World 2 of the reader's or listener's thoughts; and conversely, when a mathematician follows a proof, his World 2 acts upon his brain and thus upon World 1. This, then, is the thesis of body–mind interaction.— Karl Popper, Notes of a realist on the body–mind problem
According to Searle then, there is no more a mind–body problem than there is a macro–micro economics problem. They are different levels of description of the same set of phenomena. [...] But Searle is careful to maintain that the mental – the domain of qualitative experience and understanding – is autonomous and has no counterpart on the microlevel; any redescription of these macroscopic features amounts to a kind of evisceration, ...— Joshua Rust, John Searle
The real distinction of mind and body based on their completely diverse natures is the root of the famous mind-body problem: how can these two substances with completely different natures causally interact so as to give rise to a human being capable of having voluntary bodily motions and sensations?
...a rejection of any dualism between mind and body, and a consequent insistence on the argument that the body is never simply a physical object but always an embodiment of consciousness.
The restriction of causality to 'efficient causality' lead to the neglect of 'goal-orientation' since it was no longer necessary within [that] framework. Not considering 'goal-orientation' resulted in the neglect of 'embedment' and the consequential presupposition of 'isolation' with separation between brain, body, and environment. Neglecting 'embedment' lead to the equation of perception/action with sensory impression/movement which could be well accounted for by 'efficient causality'. Accordingly, since dominated by 'efficient causality', qualia and intentionality, as related to perception/action rather than to sensory impression/movement, were excluded from science and consequently regarded [as] purely philosophical problems. Analogous to 'final causes', 'formal causes' were eliminated as well. 'Efficient causality' is not compatible with 'embedded coding' [which] is necessarily tied with 'formal causality' and 'final causality'... Finally, the possibility of mental causation remains incompatible with 'efficient causality'. It can, however, be properly described by 'formal and final causality'.
Walter Freeman, with his usual originality, suggest that we may be looking at the whole thing in completely the wrong way when we ask whether consciousness causes or is caused by neural activity. He suggests that circular causation is a more relevant concept in this regard than linear causation. Consciousness and neural activity are certainly interdependent, but it is impossible in principle to say that either causes the other. Thus the whole concept of consciousness as agent is simply a misreading of the true situation.Through my readings in physics and philosophy, I learned the concept of circular causality, which invokes hierarchical interactions of immense numbers of semiautonomous elements such as neurons, which form nonlinear systems. These exchanges lead to the formation of macroscopic population dynamics that shapes the pattern of activity of the contributing individuals. Circular causality departs so strongly from the classical tenets of necessity, invariance, and precise temporal order that the only reason to call it that is to satisfy the human habitual need for causes. The most subtle shift is the disappearance of agency, which is equivalent to loss of Aristotle's efficient cause. The very strong appeal of agency to explain events may come from the subjective experience of cause and effect that develops early in human life, before the acquisition of language .the question I raise here is whether brains share this property with other material objects in the world. The answer I propose is that assignment of cause and effect to one's self and to others having self-awareness is entirely appropriate, but that investing insensate objects with causation is comparable to investing them with teleology and soul. The further question is: Does it matter whether or not causality is assigned to objects? The answer is "Very much." Several examples are given of scientific errors attributed to thinking in terms of linear causality. The most important, with wide ramifications, is the assumption of universal determinacy, by which the causes of human behavior are limited to environmental and genetic factors, and the causal power of self-determination is excluded from scientific consideration.
Aristotle seems to say that the nous is a form, but on closer inspection we find that it is not, or at least not the usual kind. Nous is a maker of forms. A “form of forms” is like a tool of tools, like a living body’s organ that makes tools. Nous is certainly not itself the sort of form that it makes. The hand is not a made tool (it would have to be made by yet another hand).
In Greek “tool” and “organ” are the same word. So we see: ”In the phrase “tool of tools” the first use of the word stands for a living organ, the second for an artificially made tool. In II-4 he says “all natural bodies are tools (organs) of the soul’s,” (both as food and as material from which to make tools). In English we would say that the hand is the organ of tools.
The body–mind relationship...includes the problem of man's position in the physical world...'World 1'. The world of conscious human processes I shall call 'World 2', and the world of the objective creations of the human mind I shall call 'World 3'.
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