Can neurobiology explain where the mind is ‘located’?

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14 November
10:23
November
2016

The simple answer would be no. But in another sense the answer is yes, because we’re pretty certain it’s in the brain. But within that, what we can say is that, in terms of brain systems, there are certain processes that you are more conscious of than others, so we look at those.

Very crudely, if you look at the evolution of brains, what you see is that the more complex the organism is, the more complex the cortex – the grey surface of the brain – is. The first cortical structures that appear in evolution are associated with motor control and sensory information for motor control: sensation for action. You hear a loud sound and you duck or you flinch. You don’t need to know what that sound is, you just need to know that there’s something behind you, it’s close, and you need to react to it.

"Try and consciously control your individual movements when you’re riding a bike or playing the piano, and you find you can’t do it any more"

Then somewhere later in evolution, you start to see a whole new kind of perceptual processing which, again to put it very crudely, is about recognising what’s out there: recognising faces, voices, colours. That means not just reacting to the world but having things that you, the animal, might be looking for in the world. Or if you’re a social animal, you need to recognise things about your colony’s specifics that help you find your place in the group.

So in perception we have these two different pathways. We can see them in humans. For example, we’ve got two totally different brain areas in hearing, so one is the one you use if you’re clapping along to a rhythm – this is the sensation-to-action part – but that’s completely different to the brain area you’d use to recognise speech.

What we find is that you tend to be much better at achieving conscious awareness of what’s happening in that identification pathway than you do in the sensation-to-action part. Have you ever had the experience of walking downstairs and then suddenly becoming aware of your movement and getting caught out – you don’t know which foot to put down next? That’s what can happen when you suddenly become aware of those more basic level sensory-motor processes, but you can’t make yourself quite conscious of them. Even if you want to you can’t. Try and consciously control your individual movements when you’re riding a bike or playing the piano, and you find you can’t do it any more. There are loads of processes involved in riding a bike, but you can’t articulate what they are, let alone be conscious of them as they’re happening.

"There’s a huge amount of interest in this difference, and people are starting to use incredibly sophisticated aspects of functional brain imaging"

If you’re remembering a conversation with me, you’re way more likely to remember what I’ve said than the rhythm of my speech or how you were shifting in your seat as we interacted. You’re more conscious of the former than the latter. And the sensory-motor, sensation-to-action one is, evolutionarily speaking, older. And that might suggest that elements of what we think of as consciousness must be evolutionarily recent.

There’s a huge amount of interest in this difference, and people are starting to use incredibly sophisticated aspects of functional brain imaging – really going in in detail – to see different aspects. Another example would be, there’s something called “binocular rivalry” where there’s a constant rivalry between your two eyes over which one’s image is the one you “see”. You’re completely unaware of this conflict, but you are aware of the outcome which is what you see in front of you as a coherent image. Neuroscientists use these kinds of information about how perceptual processing is structured in the brain, and where this activity is taking place, to draw this line between things you are and are not conscious of.

"You’re completely unaware of this conflict, but you are aware of the outcome which is what you see in front of you as a coherent image"

So, in one sense, consciousness is partially about what you can access in these different neural pathways: ones you can be aware of, versus processes that you simply can’t have awareness of. But what you don’t find is one part of the brain that is controlling it all. You can find parts of the brain that will keep you awake. They’re in the brain stem, which is why when you have a bang on the head, you monitor people’s consciousness, because if it starts to go down that means there’s a bleed on the brain and it’s putting pressure on the brain stem. But the brain stem doesn’t control what you’re conscious of. It controls whether or not you’re awake, but nobody would find that a satisfying answer of being the seat of consciousness. Obviously you have be awake to be conscious, but it’s not explaining how any of the rest of it is happening.

Ultimately, the best answer is that consciousness is distributed. You can find following a brain injury that people have selective deficits, that parts of their consciousness are missing. That will be a different part depending on which part of the brain is injured. But what you don’t find is people having some disorder of consciousness that affects everything – unless, as I say, you’re talking about switching off completely, i.e. being in a coma.

Even in the famous case of “left neglect” where people seem completely unaware of one whole side of space around them, they still have conscious awareness of the other side. As far as we can tell – and as with so much in neuroscience these are early days and there’s vast areas we just don’t know – consciousness is a combination of a whole set of different processes and pathways, all working together. There’s no one single part of the brain that’s governing it. 

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