The Relationship Between the Mind and the Brain
Thomas Ash

Many theories have been put forward to explain the relationship between what we call your mind (defined as the conscious thinking 'you' which experiences your thoughts) and your brain. In fact, it's fair to say that this is one of the fields of philosophy which is most up in the air (although, of course, all of philosophy is up in the air to some greater or lesser extent).

However, it is also a field for which the advancing discipline of neuroscience holds out some hope of a solution. In the last half of the 20th century we have learnt how to actually 'see' thoughts play out in the brain on magnetic imaging devices which show activity in different areas of the brain. We have learnt which parts of the brain perform which functions, although it would be wrong to depict this as a vindication of the idea behind phrenology: it is not as if discreet chunks of the brain perform discreet functions.

To some this has seemed to point to epiphenomenalism. Epiphenomenalism is the idea that consciousness is simply an effect of neural events in your brain. If you can see thoughts go on in the brain, and see how they cause neural activity correlated with other thoughts, then (the reasoning goes) all thought must go on in the brain. Epiphenomenalism is in many ways an appealing philosophy of mind, as it seems to solve one of the most mysterious problems in philosophy without denying either what science tells us or our undeniable experience of concsciousness. For this reason it was very popular among the materialistically-minded in the 19th century, before more radical options like behaviourism and the Identity Theory came on the scene.

But the fact that we can have thoughts about consciousness itself (as my ability to write this essay shows) poses a problem for epiphenomenalism, namely that of what caused these thoughts. Epiphenomenalism, as a sound, scientific-minded doctrine, is commited to saying that this must be a certain pattern of neural activity. But it cannot identify consciousness with this neural activity, for it sees the experience of consciousness as a byproduct of that activity, a kind of 'steam' given off by the engine of the brain, to use the most popular metaphor. But if this is the case then the knowledge that we are having this experience shouldn't be able to enter the causal chain of firing neurons in this place, any more than an engine can be affected by the steam which shoots out of . Epiphenomalism explicitly denies this, but interaction between mental and physical events demonstably happens, so epiphenomenalism must be wrong.

This inexplicable entry into the chain of causes which make neurons fire also poses a problem for determinism as simply understood as the following of physical laws in the brain which make one state of all the neurons in the brain necessarily lead to the next state, and then the next state after that, and so on, all in accordance with the laws of electricity and chemistry. However, this does not deal a fatal blow to determinisnm. Most theories of determinism are more complex than that, and indeed can be made completely irrespective of any "appeal to neurons." So long as conscious experiences are part of a chain of causes, and every action is ultimately fully explicable by its causes, physical and mental, determinism stands. My observation does disprove a notion of the world as operating like a peice of deterministic clockwork, in which physical events are explicable only by other physical events (this doctrine is known as physicalism) by giving a counterexample.

If my observation doesn't disprove determinism, it does deal such a fatal blow to epiphenomenalism. Because if consciousness is just a sort of secondary effect of brain activity, an experience it generates for the person in which it takes place, it shouldn't be able to be affected by it any more than anything else in the physical world could. The only possible way out of this problem for the epiphenomenalist is to claim that our belief in mental events does not in fact come from our experience of mental events, but this means some explanation has to be given of where they do come from, and also flies in the face of the undeniable fact that it definitely seems as though it does.

What does all this point to? Well besides showing that epiphenonalism cannot in fact be an accurate picture of the mind's relationship to the brain, it points to one of four other theories.

The first is one which may suit the more traditionally, or religiously, inclined, as well as seeming to provide something of a basis for free will. (Though it is actually only a superficial one - causes and reasons for thoughts and actions should exist just as much in the mental realm as in the physical one.) This is more or less the direct opposite of epiphenomenalism; rather than mental events being a direct result of physical ones, it is the other way round, and the brain merely reflects what is going on in the mind. But this has a lot of problems, not least that purely physical neuroscience (which contrary to popular belief is actually quite an advanced science, with ample evidential backing, and not speculative at all), seems to show that a lot of what goes on in the brain can be explained by the interaction of neurons, rather than being a puppet for a separate mind. One example of an event which disproves this notion is light from a comet triggering the nerves in the eyes, triggering a physical event which sets of a chain of such events which result in your seeing the comet streak across the sky. What, on this view, is the brain doing in this case?

We all know that when we alter the brain directly physically, consciousness is also affected. An example of this is the physical stimulus of light hitting the eye setting off a chain of neural events which cause mental events. The brain can also be altered to affect the mind either by mind-altering (note we call them mind-altering, though in fact they're brain-altering) drugs or more directly by anaesthetics which render you unconscious by inhibiting the action of anaesthetics by rendering you unconscious. This shows that, at least sometimes, the mind follows in the course set by the brain, rather than vice-versa. The fact that stopping neuron activity in a certain part of the brain can stop consciousness entirely suggests somethijng more - that the mind doesn't have a separate existence from the brain, but this just leaves the question of how our conscious experience feeds back to the brain still more perplexing.

The second is the idea that the mind and the brain are a two-way street; perhaps most of the time it is the brain calling up memories, doing calculations in mathematics tests and so on, but the mind also provides feedback, at least in the case of letting us think about consciousness. However, this faces a problem that the first theory, 'reversed epiphenomenalism', also shares. This is of saying exactly what 'the mental' is, how it exists if it is not an effect of brain activity, the way in which it and the brain are linked and can share each other's thoughts, and how it can initiate thoughts of its own. Given that the mind is presumably taken to be a non-physical thing (if not, where can we find it?), and thus completely different from anything we have knowledge of so far, it requires a lot of explanation. There is some work to be done here - but this option is certainly a possibility, and may ultiamtely be the only one left standing. To (loosely!) quote Sherlock Holmes: "once you have eliminated the impossible, whatever remains, no matter how improbable, must be the truth."

The third theory is somewhat out there, but is worth mentioning because it provides a novel solution to the difficulty of relating the physical to the mental. This is the idea first introducing by the 18th century philosopher - and Bishop - George Berkeley, that there is no physical, and that mental events are all that exist. The reasoning behind this was that it is difficult to see how an event of one kind can cause an event of a totally different kind. And yet in the effect the physical world has on our minds, and our minds have on our decisions to interact with the physical world, they seeming do all the time. Therefore, given the choice, we should choose mental events, which are the only type of event we directly experience, and thus know for sure exist. The mental experience of a rose is thus all there is. To explain why we all experience the same rose when there is no underlying physical reality we all live in, Berkeley responded that the rose exists as an idea in the mind of God, which we are all free to access. Of course, this God's existence is in need of some additional justification beyond his being convenient for Berkeley's theory.

Berkeley's theory faces several problems, but one will suffice for now. This is that if the mental is all that exists, it is hard to see why there would be such a complex 'illusion' as the physical brain, with all the complex neuroscience that explains how it seems to think thoughts and store memories.

The fourth and final solution is that of Identity Theory. This holds that the problem of the relationship between neural and mental events is non-existent - they are in fact the same thing. At first the problem with this seems obvious: they aren't. There is a world of difference between the physical firing of a neuron and another neuron responding to this electrical signal, and a conscious mental event. However, perhaps mental events, which are after all little understood, simply do equate to physical events and are an integral part of them. This would provide a convenient explanation of how we are able to think about our mental events - it simply equates to thinking about our neural events.

One problem with Identity Theory is that it would imply that every physical event, from the 'decisions' of a vending machine to the action of a doorhinge, has a mental correlate. It also implies, as the philosopher Jackson has pointed out, that if a computer had an absolutely complete knowledge of neuroscience it would be able to understand what consciousness is like without having experienced it. The philosophers Block and Fodor point out that it is very unlikely that there is only one possible type of neurophysiological state with which a given mental state is indentical. Consider, for example, non-human animals, or space aliens with a completely different sort of biology. Block likened Idenity Theory to a sort of "neuronal chauvinism." Then there is the fact that we can imagine the logical possibility of someone having the same brain pattern as us, but holding a somewhat different mental experience of colours, or, zombie-like, no conscious experience at all. If Identity Theory is true, this should be a nonsensical notions: like something being a dog without being a canis canis (a case of true identity.) A final problem those arguing for Identity Theory have to face is that it is very hard to provide evidence for: we don't have access to the mental events that physical actions other than those in our brain do or do not cause.

This is a problem shared by all theories of the mind-brain relationship. consciousness is by definition a private experience, accessible only to the person it belongs to, unlike other physical phenomena. This is what takes it outside the realm of science and the scientific method and into the realm of philosophy, though neuroscience can still make valuable contributions. Were it not for the problem of our ability to think about consciousness, epiphenomenalism would be the most obvious explanation. But that problem scuppers it, and suggests that there is some more significant reality to mental events than that of merely a projected image. Given our lack of understanding as to just what that nature is, and the scientific method's inability to tackle the question, it's best to admit that the question of how the mind and the brain are related remains something of a mystery... at least for now.

© 2002

About the author...
Thomas Ash is the webmaster of Big Issue Ground and Atheist Ground. He is a graduate student studying philosophy at Merton College in the University of Oxford. He received his BA in the subject from the University of Cambridge, where he was president of the University Atheist and Agnostic Society. As you may have guessed, he is an atheist - a positive one in fact. More information can be found here.

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