There’s an interesting debate going on among some neuroscientists about which parts of the brain are involved in subjective experience. On the one side are Christof Koch, Giuilio Tononi, and colleagues who argue that consciousness exists wholly in the back of the brain, that the frontal structures are not involved. On the other side are neuroscientists who, while agreeing that the back part of the brain is definitely involved, argue that the role of the front part can’t be dismissed.
To understand this debate, it’s worth doing a quick review of what is known about the functionality of the various components of the brain. (To keep things simple, I’m going to focus primarily on the neocortex, the wrinkled cover on the top of the brain. If you’re familiar with neural anatomy, this isn’t to discount the role of sub-cortical structures such as the thalamus or basal ganglia.)
Image credit: BruceBlaus via Wikipedia
The first thing to understand is that the back part of the brain seems to be dedicated to sensory perception, and the front part to planning and initiating movement. The neocortex is divided into four lobes, which are separated from each other by deep fissures.
The occipital lobe in the back is dedicated to vision. The front part of the temporal lobe on the side handles hearing. The back part of the temporal lobe handles visual recognition of objects, faces, etc. The back part of the parietal lobe handles visual perception of movement. The middle part of the parietal lobe, along with surrounding regions, appears to be involved in integration of the various senses. It’s sometimes referred to as the posterior association cortex.
A strip along the front part of the parietal lobe is the somatosensory cortex, each part of which processes touch sensations from a particular body part. It’s somewhat mirrored by a strip just across the central sulcus fissure along the back of the frontal lobe, which is the primary motor cortex involved in controlling the movement of each body part.
In addition to controlling movement, the frontal lobe also plans movement. More immediate planning happens in the regions just forward of the primary motor cortex, named appropriately enough, the premotor cortex.
As we move forward, the planning becomes progressively more forward looking and more abstract. This is the prefrontal cortex, often referred to the executive center of the brain. Its primary role is planning, including planning to plan, driving information gathering for future planning, etc. As part of its function, it acts as a conductor leading the other lobes in imagining various scenarios.
Okay, so back to the debate.
The back-only proponents cite various neurological case studies as evidence, talking about patients who had parts of their frontal lobes damaged or disconnected, but who still showed signs of being conscious. They also cite cases of patients who had a frontal lobe pathology making them unresponsive, but later recovered the use of their frontal lobes enough to relay that they were conscious the whole time, but simply lacked the will to communicate.
This kind of evidence seems problematic for a number of reasons. First, in my (admittedly inexpert) opinion, some of the cited cases in the paper seem anecdotal and based on hearsay. Second, the other cases depend on self report, which is a problem because only patients with at least somewhat functional frontal lobes can self report anything, and the accuracy of such reports hinge on them remembering their former states of mind accurately. Third, as the authors of the second paper point out, the data has something of a selection bias in it, and some of the cited evidence doesn’t check out. And finally, again as pointed out in the response paper, the exact nature of frontal lobe damage or disconnect matters, making each case unique.
But I think the actual answer to this question depends on how we define “consciousness.” If our definition only includes unfocused perception, then the back-only proponents might have a case. The problem is that we seem to perceive a lot of stuff unconsciously. And raw perception alone doesn’t quite seem to match most people’s intuition of consciousness.
That intuition also typically requires that the system have attention, emotions, imagination, and introspection.
Frontal lobe expert Elkhonon Goldberg, in his book ‘The New Executive Brain’, sees attention as a frontal lobe function. He describes the back portions of the brain as creating the stage production of subjective experience, with the audience for the resulting show being in the frontal lobes. Crucially, it’s this audience that decides what part of the show to focus on, in other words, where to direct attention.
Emotions are driven by sub-cortical structures such as the amygdala, hypothalamus, anterior cingulate cortex, and others that are sometimes referred to together as the limbic system. The signals from these structures seem to affect processing in the frontal lobe, but also the temporal lobe and the insular cortex, which exists in the fissure between the temporal and parietal lobe. In other words, emotional feeling seems to happen in both the front and back of the brain.
Imagination, simulating various action-sensory scenarios, seems to require the frontal lobes, particularly the prefrontal cortex. Not that the content of imagination takes place in the prefrontal cortex itself. It actually farms the content generation of these simulations out to the other regions, such that the vision processing centers handle the visual parts of an imagined scenario, the hearing centers handle the auditory parts, etc. The prefrontal cortex acts as the initiator, conductor, and audience, but not the content generator. Still, without the prefrontal cortex driving it, it’s hard to see imagination happening in any meaningful way.
And then there’s introspection, also known as self reflection. Without introspection, we wouldn’t even know we were conscious, so it seems vital for human level consciousness. Again, the prefrontal cortex seems heavily involved in this feedback function, although as with imagination, it depends on processing in the back portions of the brain, most likely the regions on the border between the temporal and parietal lobes.
Perhaps another way to look at this is to ask, if we somehow completely removed the brain’s frontal regions (and associated basal ganglia and thalamic nuclei), would the remaining back half still be conscious? It might have the ability to build predictive sensory models, in other words it would have perception, but the modeling wouldn’t be done with any purpose, and it wouldn’t have any mechanism to decide on what portions of those models should be focused on. Arguably, it would be a mindless modeling system.
But if we removed the rear portion and kept the frontal lobes, we’d have even less functionality since the frontal lobes are crucially dependent on the posterior ones for the content they need to do their work.
And neither of the above isolated systems would have emotions unless we retained the limbic system as part of their supporting structures.
All of which is to say, for what we intuitively think of as consciousness, we need all of the components discussed above. Subjective experience is the communication between the perception and emotion centers of the brain and the action oriented centers. Wholesale removal of any of these centers might conceivably leave us with an information processing framework, but not one most of us would recognize as conscious.
Unless of course I’m missing something?
h/t Keith Frankish and Gregg Caruso for sharing the papers on Twitter.
SelfAwarePatterns 
I think your conclusion is correct. It’s not a this or that scenario, rather a whole. Consciousness arrives in increments. Despite not possessing a single neuron, a protozoa is, at some incredibly basal level, aware of itself, for it weren’t it would not resist all assaults launched it.
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Thanks John! Not sure I’d agree on a protozoa though. It seems like its actions would be far more rigid stimulus-response programming. It doesn’t seem like there is any perception (sensory modeling), attention, or any of the rest.
But maybe there are aspects of this I’m not familiar with?
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Stimulus-response-self defense. Right or wrong, I’d argue anything that defends itself possesses some basal recognition of ‘self.’
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I see what you’re getting at. But would you include a network threat detection system in that category, or maybe a car with a collision avoidance system? If not, what would you say are the key features? Just curious.
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Self containment. Autonomy. Life wants to defend itself, and just as Dostoevsky’s character, Raskolnikov, facing execution, would have preferred to stand on a narrow ledge for all eternity, surrounded by darkness and tempest rather than die at once, it wants to hang on.
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Thanks for the clarification. It seems like that category would include plants, particularly species like Mimosa pudica that contract when touched.
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IIT certainly holds that all plants, from algae to angiosperms, possess a degree of consciousness. Granted, this awareness of self is staggeringly alien to us, to what we call the familiar, but it can be persuasively argued. And this brings us back to the original point; that consciousness is not a front or back, this or that, phenomena, rather better seen as incremental steps (rising complexity) reaching all the way back (perhaps) to proton powered rocks. Or, if we’re to believe IIT, even further back, all the way to protons.
Reading this, Tegmark would be nodding his head furiously 😉
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John, while I think conscious events do have location (and see my forthcoming response to the article for where the action is), I also can see the role of incremental steps. However, I am curious as to your take on the role of complexity in consciousness. My main gripe with IIT is that, from what I’ve read so far, IIT equates consciousness with complexity for complexity’s sake, so that you can have a system that integrates information in a stupendously complex manner, but doesn’t really do anything that we would say looks like consciousness. As the man says, what am I missing?
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Hi James, let me just say first that I really don’t have any expertise to score the merits of IIT (or its more poetic brother, panpsychism) in any convincing or meaningful way. I just published a book which dives into the subject, but that book is a work of Poe’s Law, so although I present the theory with religious verve, I really can’t comment on it in the actual world. That being said, I like the theory. It makes sense in so far as anything that hangs onto itself (hangs on to its integrated information) possesses some quality which Tononi and Koch equate to consciousness, or what they call Phi. As Koch asserts:
In my book I use the example of the hydrogen atom (in the core of a star) struggling to maintain itself against gravity and electron degeneracy pressure. It is a battle it cannot however win. Rather than paraphrase it all, this is how I present that in the book:
Even though the broader subject matter is essentially a joke, this is the core of IIT, and to me it’s rather convincing. The struggle denotes awareness of self, and the greater material complexity the more convoluted is that thing’s response is to all those things which would, if given the chance, annihilate it. For example, what took 15 million degrees to “kill” hydrogen requires an outrageous 100 million degrees for the more complex and heavier helium atom to lose its struggle and fuse into beryllium and carbon. So, if this is true, then homeostasis (the tendency to equilibrium through physiological processes) is not a unique physiological program cherished only by those things that tend to meet the criteria we ascribe to so-called ‘living’ things.
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I agree that Tegmark would be on board. He likes to say something to the effect that consciousness is what information processing feels like.
My issue with IIT is similar to James’. There are just too many systems that it includes in the conscious category. I definitely agree that integration is crucial for the common meaning of consciousness, but I can’t see that it’s sufficient, at least not for animal or human consciousness.
But ultimately “consciousness” is what we define it to be. Like many pre-scientific concepts, it doesn’t map precisely to the scientific view of the world.
On the one hand, I like that panpsychism gets some people out of the mode of privileging human mental processing, but on the other, I fear it leaves them satisfied with too incomplete an explanation of it. Tegmark’s statement, for instance, leaves open the question of what “feeling” actually is.
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Wouldn’t you say “feeling” is much like consciousness: emergent? A plant fears. We know that now. PR1, PR2, PR5 gene expression is evidence of that, but a plants “fear” is entirely alien to how we would define fear. Once again, it appears to be a matter of complexity. The capacity remains unchanged, but the depth and scope to intertact with it varies according to complexity.
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I think we should be conservative in reaching for emergence as an explanation. It seems to me that a better, more functional, more adaptive explanation is that “feeling” is communication from the emotional centers of the brain to the action oriented centers. That gives an evolutionary reason for its existence and its attributes, to influence what those action oriented centers will do.
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Hi Mike,
I feel morally bound to provide my alternative view: what if consciousness is like watching a football game on a video screen. What if the “audience” is the sub-cortical structures, and the video screen has a pixel for each neuron coming from the neocortex? What if it’s a captive audience, so doesn’t have control of the cameras? What if the sensory input (back part of cortex) is the action, and the prefrontal cortex is the color commentators. The audience hears the commentators giving directions to the cameras. The director also gives direction for zooming the camera ( is claustrum?), but occasionally there’s some action such that the camera controller will ignore the commentator to see what’s going on. The hippocampus takes notes and queues up instant replays. The emotional centers change the mood lighting and background music via twitter messages. Okay, that’s enough. Carry on.
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Hi James,
I enjoy your comments. It’s not often I get to discuss neural anatomical details with anyone.
On the sub-cortical structures, as I alluded to in the post, I don’t discount them. In fact, everything I laid out about functional locations (which incidentally is mainsteam neuroscience backed up by extensive evidence) should be read with a asterisk to include the thalamic or basal ganglia nuclei that project connections out to those cortical regions. (I didn’t cover this in the post because I suspect I was already past most people’s tolerance for technical minutia.)
For instance, when I talk about the prefrontal cortex being involved in attention, that also includes the medial dorsal nucleus and the pulvinar nucleus of the thalamus. Indeed, you could say that these nuclei are the main routines calling lower level subroutines in the cortex for the more detailed work.
So, I think these sub-cortical structures are involved as both incipient content generators and audience. The neocortex is required for our full experience, but many non-mammalian animals get by just fine with their equivalent of the thalamus and basal ganglia as their entire forebrain.
Where we differ is I can’t see the sharp division you describe with the neocortex putting on the show and the sub-cortical structures being the audience. It doesn’t seem compatible with the established functional locations. And if it were true, I don’t think we’d see any consciousness in hydranencephalics, children born without a neocortex. They usually have their thalamus, which appears to give them a primal consciousness much like that of newborns.
I’m still not sure what to make of the claustrum. It doesn’t come up in most of the neuroscience I’ve read. Koch and Crick’s position seems to be a minority one. And I think Damasio’s point that it doesn’t really have the substrate for the role attributed to it is something we should keep in mind. Of course, it could lean pretty heavily on surrounding structures such as the insular cortex, the putamen, and posterior cingulate cortex for the detailed work, much as the thalamus and basal ganglia lean heavily on the cortical regions.
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Mike, while I’m suggesting the sub-cortical structures are a captive audience, that does not mean they are a passive audience. They do things with the signals they get from the neocortex. I suggest that it is the act of doing something with the signal which generates the experience, i.e., is the experience. If the cortical neuron fires into the sub-cortical unit but nothing happens after that, there is no experience. Also, this experience is the feeling. This experience is the information processing Tegmark is talking about. This information processing is the integration of information that IIT is talking about.
Also, while the neocortex is clearly the largest/most important “screen” available to the subcortical structures, it’s not the only one. As you point out, there is the midbrain and brain stem.
Re the claustrum, I think Koch or others may have stated the possibility that it is “the seat of consciousness”, which would imply that it is the location of conscious events. I would agree with Damasio that this role would be overstated. But I do think the claustrum may prove necessary for autobiographical consciousness, and my first guess is that it’s role involves attention and/or generation of new concepts, possibly by synchronizing firing rates of neocortical groups in disparate regions of cortex under the guidance/control of the prefrontal cortex. These disparate signals would then show up at the sub-cortical structures at the same time and could thus be “combined” in some fashion. Maybe, instead of Baar’s idea of information being broadcast to a global workspace, the information instead comes (selectively, as per the prefrontal cortex via the claustrum) to the global market of the subcortical structures where it can be “integrated”.
I think that may be my new catch phrase: all roads lead to the thalamus.
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James,
It strikes me that, although we disagree on the anatomical details, we seem agree on some essential concepts. Both of us see the content of consciousness being generated in various locations, but the actual experience happening in the locations that receive that content. We both see the audience as an active component, to some degree dictating what type of information it will receive. Not sure, but I suspect we both see the audience as the action oriented aspect of the mind.
Our disagreement seems to be on where these things happen. You see the final integration happening in the thalamus. I see it happening (in healthy adult humans) in circuits that span the prefrontal cortex, the dorsal medial nucleus of the thalamus, and the pulvinar nucleus of the thalamus (and possibly more). In my view, the final result is in the thalamus, but the thalamic nuclei themselves are too small to be the full audience (again, in healthy humans).
I also agree that the experience is the information processing which is the information integration. The difference here is that I don’t think all information processing or all information integration is experience, in the same sense that while the video game Angry Birds is information processing and integration, not all information processing or integration is Angry Birds.
Reading your points about the claustrum made me think of a possibly simpler explanation for its function. As you noted, one reason Crick and Koch thought it might be coordinating consciousness is because it may be synchronizing the firing rates across the cerebrum. Maybe too much is being read into that, that synchronizing firing rates is what it does, period.
Its actual role might be similar to the system clock in a computer chip which establishes the clock rate of the processor. The claustrum’s role might be to merely set the pacing for the processing throughout the cerebrum, to make sure the brain wave rates are consistent. Many neuroscientists think that there must be pace setting neurons somewhere in the brain. Maybe the claustrum is the place. Just a thought.
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Neuroscience isn’t really my area of expertise, but I have a hard time believing that consciousness (however we define it) can be pinned down to just one region of the brain to the exclusion of all others. I’m sure certain parts or regions are more important than others, as those case studies about damage to the frontal lobes seem to illustrate. But in general, biological systems seem to turn out to be more interconnected and inter-depended than they initially appear to be, not less.
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Just as you’ve been on a chemistry dive for a while, I’ve been on a neuroscience one. In truth, I long since passed what I needed for any science fiction research purposes (more than enough to see lots of mistakes about the brain in published SF, including hard SF), but interest is making it hard for me to move on from it.
On consciousness not existing in any one place, I think your instinct about it is right. We can talk about where various aspects of it are processed, but no one piece on its own would be what we commonly call “conscious.”
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It’s interesting (and fun) how once you start learning about a science, you keep wanted to get deeper and deeper into it. Most of the stuff I learn about chemistry will probably never, ever be useful to me in my writing. On the up side, I’ve found that having some basic knowledge of chemistry makes most of the other sciences I try to study a little easier to understand.
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I’ve been surprised by how useful the basics I remembered from high school and college chemistry have been in understanding things like the evolution of stars, or biology, including neurobiology. I do sometimes wish I understood organic chemistry better, but that wish hasn’t been strong enough yet to make me learn more about it. Maybe one of these years 🙂
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