Do Neurons Produce Consciousness?

Dan Dennett casts doubt on the idea that neurons produce anything other than further neural processes and behavior in a paper published last July: “Facing up to the hard question of consciousness”  2018 Phil. Trans. R. Soc. B 373: 20170342. http://dx.doi.org/10.1098/rstb.2017.0342.  Dennett recognizes the Cartesian dualism inherent in the idea that a physical thing—the brain—produces something entirely different—consciousness, and wants to do something about it. We’ll consider Dennett’s proposed solution in a moment.

The basic idea that neurons produce consciousness is the presumption of cognitive science, which searches for the neural correlates of consciousness, the NCC. According to cognitive scientist Christof Koch,

The NCC are defined as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept…

The content‐specific NCC are the neurons (or, more generally, neuronal mechanisms), the activity of which determines a particular phenomenal distinction within an experience. For example, the NCC for experiencing the specific content of a face are the neurons that fire, on a trial-by-trial manner, whenever a person observes, imagines or dreams a face, and are silent in other circumstances. When the content-specific NCC neurons in this example are activated artificially — for example, by transcranial magnetic stimulation (TMS), electrical stimulation or optogenetic stimulation — the participant should see a face even if none is present, whereas if their activity is blocked, the participant should not be able to see a face even if one is present. (“Neural correlates of consciousness: progress and problems”  Christof Koch, Marcello Massimini, Melanie Boly and Giulio Tononi, 2016 Nature Reviews Neuroscience vol 17)

The contents of consciousness are determined by the neural activity. Neurons are the cause, conscious percepts are the effect. They are not identical items. Under normal circumstances, observation of the outside world activates the appropriate neurons to fire. But imagination, dreams, or artificial stimulation can also cause the conscious percept—of a face in Koch’s example. And if the necessary neuronal activity is blocked, you won’t see a face even if you are staring at one.

So, yes. Neurons produce consciousness. Earlier, Koch put the schema in a diagram:

koch color diagram.jpg

Light from the outside world enters the man’s eyes and is transduced into information in the form of spike trains. Wayne Wu:

A neuroscientific explanation of consciousness adduces properties of the brain, typically the brain’s electrical properties. A salient phenomenon is neural signaling through action potentials or spikes. A spike is a large change in electrical potential across a neuron’s cellular membrane which can be transmitted between neurons that form a neural circuit. For sensory neurons, spikes are tied to receptive fields. For example, in a visual neuron, its receptive field is understood in spatial terms and corresponds to that area of external space where an appropriate stimulus triggers the neuron to spike. Given this correlation between stimulus and spikes, the latter carries information about the former. Information processing in sensory systems involves processing of information regarding stimuli within receptive fields. (forthcoming in SEP, “Neuroscience of Consciousness”)

The light from the outside world takes on a completely different form inside our body. The light reflected from objects carries information we need about those objects. We have no light inside our bodies, so the light, or the information in the light, is transduced into neural impulses. The light takes on a completely different form, but the information is preserved.

Once in the brain, the spikes are organized into NCC. So far, no part of this process is conscious. Everything is accomplished via preconscious bio-chemical mechanisms. Conscious experience is possible only because in the final act, NCC produce the conscious percept. In Koch’s diagram, that production is represented by the arrow to the right pointing to the red dog. The production is a second transduction from neuronal activity into a mental image. That we have any conscious experience at all is due to the second transduction.

This reasonable picture is the foundation of the traditional mind/body problem and has occupied much of philosophy since Descartes. Though scientists rarely put it quite this way, the realm of the conscious percepts is separate from  both the body and the outside world. That would mean the world consists of two fundamental parts, the mental and the physical. According to Maxwell Bennett and Peter Hacker,

The greatest figures in the first two generations of 20th century neoscientists, e.g. Sherrrington, Eccles, and Penfield, were avowed Cartesian dualists. The third generation retained the basic Cartesian structure but transformed it into brain-body dualism: substance dualism was abandoned, structural dualism remained. For neuroscientists now ascribe much the same array of mental predicates to the brain as Descartes ascribed to the mind and conceive of the relationship between thought and action, and experience and its objects, in much the same way as Descartes—essentially replacing the mind by the brain. The central aim of our book Philosophical Foundations of Neuroscience was to demonstrate the incoherence of brain/body dualism and to disclose its misguided crypto-Cartesian character. (Neuroscience and Philosophy: Brain, Mind and Language p. 131, with chapters by Daniel Dennett, John Searle and Daniel Robinson, Columbia UP 2007) 

Bennett is a neuroscientist; Hacker is a Wittgenstien scholar. Whether their diagnosis is correct, the point is that dualism is tough to escape from, even in science.

Dan Dennett wants to stop the mind/body problem before it starts. In his new paper “Facing up to the hard question of consciousness”, he says the mistake is in thinking that there is a second transduction.

There is no double transduction. The various peripheral and internal transducers—rods and cones, hair cells, olfactory epithelium cells, stretch-detectors in muscles, temperature-change detectors, nociceptors and others— are designed by evolution to take the occurrence of physically detectable properties as input and yield signals— axonal spike trains—as output. There is no central arena or depot where these spike trains become recipes for a second transduction that restores the properties transduced at the periphery, or translates them into some sort of counterpart properties of a privileged medium. Vision is not television, audition does not strike up the little band in the brain, olfactory perception does not waft aromas in any inner chamber. (Nor, one had better add, are there subjective counterpart properties, subjective colours-that-are-not-seen-with-eyes, inaudible-sounds, ghost-aromas that need no molecular vehicles, for us to enjoy and identify in some intimate but unimaginable way.) Colour vision is accomplished by a sophisticated system of information processing conducted entirely in spike trains, where colours are ‘represented’ by physical patterns of differences in spike trains that are not themselves colours. The key difference between the transmission of colour information by a DVD and the transmission of colour information by the various cortical regions is that the former is designed by engineers to be a recipe for recreating (via a transduction to another medium) the very properties that triggered the peripheral transducers that compose the megapixel screens behind the camera lens, while the latter is designed by evolution to deliver useful information about the affordances that matter to the organism in a form that is readily usable or consumable by the specialized circuits that modulate the behaviours of systems external and internal.

 So, there is no place in the system for qualia, if they are conceived of as intrinsic properties instantiated by (as contrasted with represented by) some activities in the nervous system.

But without the second transduction, how do neurons produce consciousness? Apparently they do not, according to Dennett. He solves the mind/body problem by eliminating mind, though he never quite puts it that way. Let’s look at Dennett’s fascinating thesis in detail.

1) The various peripheral and internal transducers—rods and cones, hair cells, olfactory epithelium cells, stretch-detectors in muscles, temperature-change detectors, nociceptors and others— are designed by evolution to take the occurrence of physically detectable properties as input and yield signals— axonal spike trains—as output.

This is the first transduction. The physically detectable properties contain information animals need to navigate the world and survive. That’s perception. The assorted physical properties in nature are transduced in spike trains.

2) There is no central arena or depot where these spike trains become recipes for a second transduction that restores the properties transduced at the periphery, or translates them into some sort of counterpart properties of a privileged medium.

There must be some way the brain processes the information from the axonal spike trains into a coherent model of the outside world. Information from sight and sound must be gathered together and coordinated into the perception of a dog, for example. What Dennett denies is that the disparate sources of information are coordinated into a conscious percept that resembles what it is a perception of. Koch’s diagram shows the NCC assembling themselves in a recipe to produce the conscious percept. That would be the second transduction of neuronal activity into consciousness. Without that second transduction, where does consciousness come from?

3) Vision is not television, audition does not strike up the little band in the brain, olfactory perception does not waft aromas in any inner chamber. (Nor, one had better add, are there subjective counterpart properties, subjective colours-that-are-not-seen-with-eyes, inaudible-sounds, ghost-aromas that need no molecular vehicles, for us to enjoy and identify in some intimate but unimaginable way.)

Dennett’s cute phrases are tough to deny. No TV or little band in the brain! How could anyone be so silly as think that! The problem, however, is that there are no colors, sounds or aromas in the mind-independent physical world. Only in your little “inner chamber.” There are no “colors seen with eyes”, because physical light reaching your eyes has only wavelength, no color. There are no “audible sounds” because the air waves reaching your ears has only frequency, no sound. No “aromas on molecular vehicles”, only molecules floating in the air. Philosophy has been familiar with this problem since the 17th century, and recent decades have seen heroic attempts to get around it.

4) Colour vision is accomplished by a sophisticated system of information processing conducted entirely in spike trains, where colours are ‘represented’ by physical patterns of differences in spike trains that are not themselves colours.

This is true, so why the scare quotes around ‘represented’? Color can be represented in a variety of ways: e.g. the word “red” or 700nm, the wavelength of light that causes a red experience. Somehow the information about the wavelength of the light that hits our eyes has to be represented in the spike trains. But we don’t just ‘represent’ red, we experience it. Objects are not red, light is not red, spike trains are not red, information is not red. So what is?

5) The key difference between the transmission of colour information by a DVD and the transmission of colour information by the various cortical regions is that the former is designed by engineers to be a recipe for recreating (via a transduction to another medium) the very properties that triggered the peripheral transducers that compose the megapixel screens behind the camera lens, while the latter is designed by evolution to deliver useful information about the affordances that matter to the organism in a form that is readily usable or consumable by the specialized circuits that modulate the behaviours of systems external and internal.

The camera takes in light reflected off actors and digitizes the wavelength information into a form that TV screens downline can use  to create new light with similar wavelengths. So the TV viewer experiences colors as similar as possible to what she would have seen had she witnessed the actors live. Light into the camera, light out via the TV screen. Our eyes are something like cameras, and the spike trains in the optic nerve represent wavelength information and carry it into the brain. And then what happens?

Cognitive science says that we get a conscious percept, such as of a red dog. Dave Chalmers famously designated the problem of how neural mechanisms produce conscious experiences as “the hard problem” in 1995, and he and Dennett have been arguing about it ever since. Turning neural mechanisms into conscious experiences would be the “second transduction” Dennett is so anxious to deny.

Dennett wants to substitute a “hard question” in place of Chalmers’ “hard problem”. That question is “And then what happens?” But Dennett does not mean to be asking how color, sound and aroma mysteriously enter consciousness. He means simply that neuroscience should get busy and track the further information processing leading to behavioral responses or whatever happens next.

What happened to color, sound and aroma? Dennett denies that there are no such things as qualia.

6) So, there is no place in the system for qualia, if they are conceived of as intrinsic properties instantiated by (as contrasted with represented by) some activities in the nervous system.

We do conceive of qualia as the conscious percepts instantiated by activities of the nervous system. Where else could color, sound and aroma come from? The wavelength of light becomes color, the frequency of airwaves becomes sound, the detection of molecules in the air becomes aroma. Qualia have a special place in the system. They are the payoff of experience.

The last word, for now, goes to a friend of Dennett’s quoted in his paper, Richard Power:

We know that our perceptions or imaginings of trees, faces, etc. are distinct from the objects themselves. They are internal representations, representations in our minds.

We understand the concept of representation from external representations, such as pictures, or verbal descriptions. For these representations we can have direct experience of both a representer (e.g. portrait painting) and a representee (e.g. the person painted). Call these the medium and the content. Thus for the Mona Lisa, the medium is a painting that hangs in the Louvre; the content is an Italian woman who modelled for the artist centuries ago. Oval partly-brown patches in the painting resemble the oval brown eyes of the Italian lady.

This is the conceptual scheme that we bring to internal representations, because it is the only one we have. But there is a huge difference. For external representations we can experience both medium and content, oil on canvas as well as people, trees, or whatever. But for internal representations, we do not experience the medium AT ALL. Only the content. The idea of a spiritual consciousness arises from the illusion that we DO experience the medium of our internal representations.

In short, we conceptualize the medium of our internal representations by abstracting some features from the content, and attributing them to some kind of spiritual or ghostly substance. That is the best we can do, because actually we cannot experience the medium at all and have to look for analogies in the external world. The idea that the medium is some state of the brain seems intuitively absurd, so powerful is the illusion that we are dealing with an iconic representation in a medium of spirit.

A medium of spirit? This deserves further consideration.

1 Comment

  1. I think the really hard question of consciousness is harder than whether consciousness can be found in neurons.

    The really hard question is despite whether we do find consciousness in neurons, there is no proof that the consciousness which is coming upon such a discovery is subject to that discovery, for the finding of that does not prove that I am witnessing something about my consciousness or only the consciousness which is find in things I am doing science upon.

    Have you found anyone trying to answer this question? Because what everyone seems to have defined as “the hard question” is actually fairly easy; it may be difficult to find the correlations in the field of view, but it is not as difficult as finding out why I would automatically figure that the neurons at the end of my scalpel or microscope equates to my witnessing of that event.

    Like

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