The mind-body problem is the philosophical and scientific consideration of the relation between conscious mental activity such as judgment, volition, and emotion and the underlying physical plant that supports this activity, consisting primarily of the brain (seen as a complex of neurons, synapses and their dynamic interactions), but also involving various sensors throughout the body, most notably the eye, ear, mouth, and nose.
A distinction is often made in the philosophy of mind between the mind and the brain, and there is some controversy as to their exact relationship. Narrowly defined, the brain is defined as the physical and biological matter contained within the skull, responsible for all electrochemical neuronal processes. More broadly defined, the brain includes the dynamical activity of the brain, as studied in neuroscience. The mind, however, is seen in terms of mental attributes, such as consciousness, will, beliefs or desires. Some imagine that the mind exists independently of the brain, and some believe in a soul, or other epiphenomena. In the field of artificial intelligence, or AI, so called strong AI theorists, say that the mind is separate from the brain in the same way that a computer algorithm exists independent of its many possible realizations in coding and physical implementation, and the brain and its 'wiring' is analogous to a computer and its software.
A more societal approach views the mind as a public construct involving the interaction of the individual with their culture and mores. The mind also might be thought to include aids that extend consciousness in ways inaccessible to the unassisted brain (for example, consciousness could be dependent in part upon processing by external devices like a computer or even an iPhone.) The physical plant also need not be restricted to one brain, but could be a combination of multiple brains in communication."
The brain is hugely complex, with perhaps as many as 10,000 different types of neuron, each with different intrinsic properties that use many different signalling systems. Altogether in the human brain there are about 100 billion neurons, each making perhaps 10,000 synaptic connections - but as well as communication by synapses these neurons also intercommunicate by autocrine, paracrine, and neurohormonal chemical signals. Neuroscientists believe that neurons and the(mainly) chemical signals that pass between them are the fundamental units of information in the brain, that these signals interact with the intrinsic properties of individual neurons to generate patterns of electrical activity within those neurons, and that these patterns in turn determine what chemical messengers are made and when they are released. Experience alters the patterns and strengths of connectivity between neurons, and neuroscientists believe that this is the basis of learning.
Neuroscientists have found that some patterns of neural network activities correlate with some mental states, and have identified regions of the brain that participate in various personality disorders, mood disorders, addictions, and dementias, such as Alzheimer's disease. The figure shows a sampling of the many known human brain areas. Brodmann labeled many more. Brodmann's area 25 located deep in the frontal lobe is implicated in long-term depression. The prefrontal cortex is involved in decision making, judgment, planning for the future. The amygdala is involved in emotion. The hippocampus is involved in memory. The insula is involved in bodily somatic sensations; it receives and interprets sensory information from organs in the joints, ligaments, muscles, and skin. The hypothalamus is involved in appetite and drive. It should be noted, however, that the activities of these regions are not entirely localized, but are coupled by the brain's circuitry, not in a static, fixed manner, but in an ever-changing dynamic manner.
Conventionally, neuroscientists assume that consciousness ("self awareness") is an emergent property of computer-like activities in the brain's neural networks, a view called connectionism. In massively complex systems like the brain, complexity can give rise to unexpected higher order activities, so-called emergent properties, not easily foreseen from the properties of individual neurons, but related to their cooperative behavior. Well-known proponents of such views are Karl Popper and John Eccles.
Such emergent properties are very difficult to work with and understand, precisely because they arise unpredictably in highly complex systems. Nevertheless, an important part of contemporary neuroscience is the understanding of neuronal networks and the relations between network behavior and the behavior of single cells, and to study how higher order behaviors emerge from the properties of the component units from which networks are built.
According to some, the 'mind' is not coterminous with the brain. As Schrödinger has suggested,
- "Every man's world picture is and always remains a construct of the mind and cannot be proved to have any other existence, yet the conscious mind itself remains a stranger within that construct, it has no living space in it, you can spot it nowhere in space...We have entirely taken to thinking of the personality of a human being...as located in the interior of its body. To learn that it cannot really be found there is so amazing that it meets with doubt and hesitation, we are very loath to admit it." And later (p. 123):
- "It is very difficult for us to take stock of the fact that the localization of the personality, of the conscious mind, inside the body is only symbolic, just an aid for practical use."
Aspects of cognitive science and cultural psychology suggest that indeed the mind is not coterminous with the brain, because the mind is a product of interaction between individuals and their culture, which resides outside any single brain, to say the least: "Culture produces the mind; brain circuitry does not." Ratner continues: "The mind-body problem of how the physical body/brain produces mental, subjective qualia, is the wrong way to frame the origin of consciousness."
- "Friends joke that I should get the iPhone implanted into my brain. But if Andy Clark is right, all this would do is speed up the processing and free up my hands. The iPhone is part of my mind already."
Interest in the mind-body problem has a history going back many millennia, with some of the early writing credited to the Stoics who believed in fate determining the course of events, and yet felt one must as a matter of being human, think through one's choices. This division has been re-invented over and over again in various forms of dualism, encompassing various attempts to answer the question "What makes us who we are?", one issue being the interpretation of the experience of conscious intention or free will.
These issues may be viewed as an empirical matter, something to be settled by careful observation, and indeed a great deal has been learned about the mechanisms of various mental phenomena such as emotion, addiction, psychological conditioning and so forth. But a fundamental stumbling block to the empirical program is that mental states are introspected and the best an empirical approach can do is to establish correlations between subjective mental states and observable brain activity. These observations are echoed by experimentalists studying brain function:
"...it is important to be clear about exactly what experience one wants one's subjects to introspect. Of course, explaining to subjects exactly what the experimenter wants them to experience can bring its own problems–...instructions to attend to a particular internally generated experience can easily alter both the timing and he content of that experience and even whether or not it is consciously experienced at all." Susan Pockett, The neuroscience of movement
A more epistemological description is provided by Northoff of the Institute of Mental Health Research: 
"Epistemically, the mind is determined by mental states, which are accessible in First-Person Perspective. In contrast, the brain, as characterized by neuronal states, can be accessed in Third-Person Perspective. The Third-Person Perspective focuses on other persons and thus on the neuronal states of others' brain while excluding the own brain. In contrast, the First-Person Perspective could potentially provide epistemic access to own brain...However, the First-Person Perspective provides access only to the own mental states but not to the own brain and its neuronal states." Georg Northoff, Philosophy of the Brain: The Brain Problem, p. 5
These observations suggest the possibility that phenomena of consciousness and neurology inhabit different realms, and it is confusion to try to explain introspected experiences using a neurological approach that by its very nature excludes the effects of observation upon what is observed. As Niels Bohr would have it, descriptions of conscious states like intention are in a complementary relation to empirical observation, one must choose one description or the other and not try to combine them:
"For instance, it is impossible, from our standpoint, to attach an unambiguous meaning to the view sometimes expressed that the probability of the occurrence of certain atomic processes in the body might be under the direct influence of the will. In fact, according to the generalized interpretation of the psycho-physical parallelism, the freedom of the will is to be considered as a feature of conscious life which corresponds to functions of the organism that not only evade a causal mechanical description but resist even a physical analysis carried to the extent required for an unambiguous application of the statistical laws of atomic mechanics. Without entering into metaphysical speculations, I may perhaps add that an analysis of the very concept of explanation would, naturally, begin and end with a renunciation as to explaining our own conscious activity."...
|"...On the contrary, the recognition of the limitation of mechanical concepts in atomic physics would rather seem suited to conciliate the apparently contrasting viewpoints of physiology and psychology. Indeed, the necessity of considering the interaction between the measuring instruments and the object under investigation in atomic mechanics exhibits a close analogy to the peculiar difficulties in psychological analysis arising from the fact that the mental content is invariably altered when the attention is concentrated on any special feature of it." –Niels Bohr, Light and Life|
Although not recognizing Bohr's point, some believe a "non-materialist" approach is necessary to understand consciousness:
|"What interests me is the alternative hypothesis that biological evolution is responsible for the existence of conscious mental phenomena, but that since those phenomena are not physically explainable, the usual view of evolution must be revised. It is not just a physical process." –Thomas Nagel, Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False|
These cautionary remarks are not endorsed universally, and many believe an empirical approach can succeed, although such answers still elude us. For example, the statement is found in many books:
|"...consciousness is a biological process that will eventually be explained in terms of molecular signaling pathways used by interacting populations of nerve cells.." –Eric R. Kandel, In Search of Memory: The Emergence of a New Science of Mind - |
According to this school of thought, a better understanding of how complex systems (like the brain) involving feedback mechanisms that as yet defy analysis ultimately will show mental states are related to cooperative actions of neurons and synapses, perhaps analogous to emergent phenomena seen in many other complex systems. Along these lines, Freeman introduces the replacement of "causality" by what he calls "circular causality" to "allow for the contribution of self-organizing dynamics", the "formation of macroscopic population dynamics that shapes the patterns of activity of the contributing individuals", applicable to "interactions between neurons and neural masses...and between the behaving animal and its environment"
It should be pointed out that the proponents of the neurological explanations of consciousness recognize some difficulties with this program. "What we do not understand is the hard problem of consciousness – the mystery of how neural activity gives rise to subjective experience."
Neurological studies of motor control and decision making suggest that subconscious actions of the brain can be more rapid than conscious mental actions, and these results have led many to reassess the role of mind in human activity. For example, the neuroscience of fear shows that emotion and instinct stem from the amygdala, and these reactions are much faster than conscious reason. The suggestion is that a conscious awareness of the role of these underlying emotional strands in our thinking might lead to better conscious decisions in the long run.
Studies of the timing between actions and the conscious decision show similar results. A subject's declaration of intention to move a finger appears after the brain has begun to implement the action, suggesting to some that unconsciously the brain has made the decision before the conscious mental act to do so. Some believe the implication is that free will was not involved in the decision and is an illusion. The first of these experiments reported the brain registered activity related to the move about 0.2 s before movement onset. However, these authors also found that awareness of action was anticipatory to activity in the muscle underlying the movement; the entire process resulting in action involves more steps than just the onset of brain activity.
The study of brain activity over longer time scales needs more attention. The time scales involved in motor control are very short, and motor control involves a great deal of unconscious action, with much physical movement entirely unconscious and not a matter of intention at all. On that basis "...free will cannot be squeezed into time frames of 150-350 ms; free will is a longer term phenomenon" and free will is a higher level activity that "cannot be captured in a description of neural activity or of muscle activation..." 
The implications of these studies appear complex, and remain a topic of discussion.
Learning is closely related to aspects of mind such as memory and judgment. Conventional wisdom is that learning takes place through changes in synapses, changes that take place over many different time scales. One model of such learning is known as Hebb's postulate: "neurons that fire together wire together."
"Many of the behavioral traits that distinguish humans from other species are molded throughout development by an exceptional capacity to incorporate experience and learning into the production of culture. This ability to learn results from changes that occur in the organization of the brain as the result of experiences. The cerebral cortex is continually remodeled in response to various molecular signals, as well as environmental stimuli. This phenotypic plasticity in the brain can occur at multiple levels, ranging from large-scale remapping of cortical areas to more subtle strengthening or weakening of synaptic connections." –Kirstin N. Sterner et al.; Dynamic Gene Expression in the Human Cerebral Cortex Distinguishes Children from Adults
An additional mechanism for learning is at the level of the DNA itself. By influencing a network of chemical switches within our cells collectively known as the epigenome, transference of environmental response to the next generation is possible. Environmentally altered switch settings account for the difference in susceptibility of identical twins to disorders like Alzheimer's disease.
- John R Searle (1997). John Haugeland, ed: Mind Design II: Philosophy, Psychology, and Artificial Intelligence, 2nd ed. MIT Press, p. 203. ISBN 0262082594.
- Carl Ratner (2011). Macro Cultural Psychology: A Political Philosophy of Mind. Oxford University Press, p. 96. ISBN 0199706298. “Culture produces the mind; brain circuitry does not.”
- Andy Clark (2008). Supersizing the Mind : Embodiment, Action, and Cognitive Extension. Oxford University Press, p. ix. ISBN 0195333217.
- Carl Ratner (2011). Macro Cultural Psychology: A Political Philosophy of Mind. Oxford University Press. ISBN 0199706298.
- Gerhard Roth (2002). “Is the human brain unique?”, Maksim Stamenov, Vittorio Gallese, eds: Mirror Neurons and the Evolution of Brain and Language. John Benjamins Publishing, p. 70. ISBN 9027251665.
- For example, see Karl Raimund Potter, John C Eccles (1984). The Self and Its Brain. Routledge, p. 35. ISBN 0415058988. “Each level is open to causal influences coming from lower and higher levels...This bears of course heavily upon the mind-body problem, upon the interaction between the physical World 1 and the mental World 2.” Accessible on line using Amazon's 'look inside' feature.
- Reprinted in Erwin Schrödinger (2012). “Mind and Matter”, Forward by Roger Penrose: What is Life?: With Mind and Matter and Autobiographical Sketches. Cambridge University Press, p. 122. ISBN 1107604664.
- Chrysippus (279 – 206 BC) attempted to reconcile the inner with the outer worlds by suggesting the mind ran under different rules than the outer world. See for example, Keimpe Algra (1999). “Chapter VI: The Chyrsippean notion of fate: soft determinism”, The Cambridge History of Hellenistic Philosophy. Cambridge University Press, p. 529. ISBN 0521250285.
- Robinson, Howard (Nov 3, 2011). Edward N. Zalta ed:Dualism. The Stanford Encyclopedia of Philosophy (Winter 2011 Edition).
- Joseph E. LeDoux (2003). “Chapter 1: The big one”, Synaptic Self: How Our Brains Become Who We Are. Penguin Books, p. 1 ff. ISBN 0142001783. Rene Descartes' famous answer was cogito, ergo sum.
- Susan Pockett (2009). “The neuroscience of movement”, Susan Pockett, WP Banks, Shaun Gallagher, eds: Does Consciousness Cause Behavior?. MIT Press, p. 19. ISBN 0262512572.
- A rather extended discussion is provided in Georg Northoff (2004). Philosophy of the Brain: The Brain Problem, Volume 52 of Advances in Consciousness Research. John Benjamins Publishing. ISBN 1588114171.
- Niels Bohr (April 1, 1933). "Light and Life". Nature: p. 457 ff. Full text on line at us.archive.org.
- Thomas Nagel (2012). Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False. Oxford University Press, pp. 49-50. ISBN 0199977194.
- This quote is from: Eric R. Kandel (2007). In Search of Memory: The Emergence of a New Science of Mind. WW Norton, p. 9. ISBN 0393329372. However, the same language can be found in dozens of sources. Some philosophers object to the unsupported statement of such conjectures, for example, observing that consciousness has yet to be shown to be a process at all, never mind a biological process. See Oswald Hanfling (2002). Wittgenstein and the Human Form of Life. Psychology Press, pp. 108-109. ISBN 0415256453.
- J. A. Scott Kelso (1995). Dynamic Patterns: The Self-Organization of Brain and Behavior. MIT Press, p. 16. ISBN 0262611317. “An order parameter is created by the correlation between the parts, but in turn influences the behavior of the parts. This is what we mean by circular causality.” Kelso also says (p. 9): "But add a few more parts interlaced together and very quickly it becomes impossible to treat the system in terms of feedback circuits. In such complex systems, ... the concept of feedback is inadequate.[...] there is no reference state with which feedback can be compared and no place where comparison operations are performed."
- Walter J Freeman (2009). “Consciousness, intentionality and causality”, Susan Pockett, WP Banks, Shaun Gallagher, eds: Does Consciousness Cause Behavior?. MIT Press, p. 88. ISBN 0262512572.
- Eric R. Kandel (2007). In Search of Memory: The Emergence of a New Science of Mind. WW Norton, p. 382. ISBN 0393329372.
- Robin A. Hurley, Katherine H. Taber (2008). “The amygdala and fear”, Windows to the Brain: Insights From Neuroimaging. American Psychiatric Publishing, p. 161. ISBN 1585623024.
- David Ropeik (September 30, 2012). Inside the mind of worry. Gray matter. The New York Times.
- Benjamin Libet et al. (1983). "Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential).". Brain 106: 623-642.
- Lars Strother, Sukhvinder Singh Obhi (2009). "The conscious experience of action and intention". Exp Brain Res 198: 535-539. DOI:10.1007/s00221-009-1946-7. Research Blogging.
- A brief discussion of possible interpretation of these results is found in David A. Rosenbaum (2009). Human Motor Control, 2nd ed. Academic Press, p. 86. ISBN 0123742269.
- Shaun Gallagher (2009). “Chapter 6: Where's the action? Epiphenomenalism and the problem of free will”, Susan Pockett, William P. Banks, Shaun Gallagher: Does Consciousness Cause Behavior?. MIT Press, 119-121. ISBN 0262512572.
- John Parks Le Tellier (2006). “Hebb's postulate”, Quantum Learning & Instructional Leadership in Practice. Corwin Press, p. 48. ISBN 1412939909.
- Kirstin N. Sterner et al. (May 30, 2012). "Dynamic Gene Expression in the Human Cerebral Cortex Distinguishes Children from Adults". PLOSǀOne; A peer-reviewed open access journal.
- Yongsheng Liu (September 2007). Like father like son. A fresh review of the inheritance of acquired characteristics. EMBO Reports. The European Molecular Biology Organization EMBO Rep. 2007 September; 8(9): 798-803. PMC1973965 DOI=10.1038/sj.embor.7401060
- Diego Mastroeni et al. (2011). "Epigenetic mechanisms in Alzheimer’s disease". Neurology of aging 32: pp. 1161-1180.