Sunday, May 02, 2010

What is the purpose of the cerebral cortex?

The main part of the human brain is the cerebrum, the big piece of folded, wrinkly meat that covers the older, more primitive “snake brain” or limbic system and brainstem. Different areas of the cerebrum support different cognitive and bodily functions. In nearly all mammals, the brain has an extremely thin (no more than two-tenths of an inch thick) wrapper around it made up of neurons, and that is the cerebral cortex (“cortex” comes from the Latin for “cap.”). The cortex, thin though it is, actually is made of even thinner layers of cells, up to six distinct layers of so-called gray matter. While there are connections in and out of the cortex to the cerebrum underneath, more than 99% of cortical activity takes place strictly within the cortex alone.

Most animals do not have a cerebral cortex. Only mammals do, and among mammals, the human version is the largest and most complex. If billions of animals get along just fine without a cerebral cortex, it raises the question, what is it for? That is a mystery.

We know that sensory signals coming from the receptors eventually end up in the cortex. Visual data, for example, ends up at the back of the head in the so-called visual cortex. What it does there, we do not know. And we know that parts of the cortex send signals out to the muscles, presumably as part of coordinated actions. But what about the 99% of a cortex’s activity that goes on within the cortex itself? What is that about?

We don’t know what the function of the cortex is, but scientists believe, based on observations of people with brain damage, and on animal studies, that somehow, activity in the cerebral cortex produces meaningful experience of the world, and also, somehow, abstract thinking, planning and language. How that could be possible is a mystery, but that seems to be what is going on.

What’s the great mystery? The mystery is that we don’t know how a physical organ like the cortex could produce mental functions like thinking, planning, and language understanding. According to the principles of science, it is not actually possible. No physical activity can produce any nonphysical effect (energy is “physical”) like a thought. Why not? Because if it did, that would violate the law of conservation of matter and energy (and many other laws of nature besides), and if that can happen, well, then we don’t know anything about anything.

E=MC2 is only true because of the law of conservation of matter and energy, for example. Violate that law and you have nothing.

And it’s not just a matter of preserving the integrity of science’s precious little formulas. We can’t even conceive of how a physical thing like a group of neuron, which are just protein, fat, and a few chemicals, could cause or create something as intangible as an abstract thought or even the experience of color. How would that work ? It would have to be magic. We can’t think of any example of any machine, no matter how complex or fantastic, that could do such a thing.

Some scientists have become so frustrated with this problem that they have just declared that thoughts, experiences, and other intangible mental phenomena do not exist, except as illusions. But that is just crazy talk. Even an “illusion” is a mental phenomenon.

Despite this impenetrable mystery, we still want to ask, what is the cortex for and why do we have one, because its occurrence is quite rare in evolution.

1. Does the cortex produce or create the conscious mind in some way? That is scientifically impossible and even unintelligible, for reasons just described. Parts of the cortex are proven to be correlated with aspects of the conscious mind, but we cannot explain that correlation.

2. Does the cortex create and store a map of the whole body, including its history and modifications? Some scientists think so (e.g., Antonio Damasio). That would require an awful lot of capacity, since the body has a lot of parts and a very long history. Still, it might be possible. But what good would it do to have such a map? Who would look at it? There is no little man in the head.

3. Could the cortex have/be historical record of bodily connections as suggested above, not used as a map, but rather, as some kind of a switchboard, so that signals incoming to the brain get routed to the correct output action signals? That seems highly implausible to me, since there are an infinite number of possible combinations and sequences of sensory information that one encounters every day and just as large a number of movements that could be made in response. The brain is very large and complex, but it is not infinite in capacity, and the cortex is, after all, only 4 millimeters thick. Also, such a “switchboard” or “blackboard” hypothesis does not allow any scope for creative action, if every input is wired to an output or even to a selection of outputs. Some scientists deny that there is any such thing as creativity, but I am quite sure they are wrong.

4. Here is my hypothesis about what the cortex is for. I think it supports intersubjective social life. Intersubjectivity is a kind of empathy that allows humans to understand each other, and that’s what is necessary to have complex civilization like ours. Without empathy, there could be no poetry, no arts of any kind, no jurisprudence, no government, no sports, no teaching and learning, not even symbolic language.

Since we are the only species that indulges such things with such intensity, it makes sense that we have the most developed cerebral cortex. Chimps have societies and maybe elephants grieve over their dead. Most mammals have a cerebral cortex and so most are intersubjective to some degree. But no other mammals use symbolic language or have courts of law or try to entertain each other. We are the only ones with a hyper-developed cortex.

How would it work? It has been proven that the brain does physically change in response to learning and adaptation. So it is plausible to imagine that the cortex is a matrix for social learning. It stores all the intermediate states on the long social journey each one of us takes from infancy to adulthood and on to the grave.

The cortex does not store individual experiences as you would store marbles in a bag, but it would store developing subsystems. You need some kind of storage to accumulate and integrate experience over time, experience like complex social understanding; like intersubjective social learning. It is the skills of social mind-reading that are accumulated and integrated and refined in the cerebral cortex.

Those cortical representations of complex social understandings are not retrieved, as from a file (because there is nobody to read such a file anyway). Rather the representations are the basis for creatively responding to new social situations. They form the basis for creative projection beyond what is known, to what might be, and at the same time, they constrain creativity to what is feasible and acceptable within the social community. So each time a new situation comes up (and every situation is new in some way), you do not need to start from square one. You start your response from what you already have in the vast network of your cerebral cortex and creatively project something from that.

Where does that creative urge or impetus come from? I don’t know. That’s the magic part.


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  2. I love this article... fascinating and well written~!

  3. Way cool. I wonder if the intersubjectivity social life theory of why the cortex exists and how humans differ than other mammals, as well as connections between the cortex and cerebrum (the avg. of 1% or whatever in MOST people) have anything to do with the development of autistic spectrum disorders. My hypothesis after reading this is that, perhaps, autism develops as a predispositioned genetic response affecting the cortex's connections to other regions of the brain. This would explain, if the theory of intersubjectivity is correct, the social outcomes of autism. It could also explain much of the sensory dysfunction, because, as you said, all sensory information from the external goes into the brain and eventually reaches the cortex. This is where it is interpreted and a behavioral outcome and feeling is produced. Think about self injurious behaviors in autistic patients. It is well known from case studies and self reports of patients with autism that sensory dysfunction is in fact occurring during times of "fits" and self injurious behaviors. What if this is due to a glitch in the cortex?

  4. You might be on to something there, Rianne. Dan Zahavi is a researcher on autism and supports the idea that the disorder is primarily a dysfunction of the social self. My review of one of his books, "Subjectivity and Selfhood" is at the link below (copy and paste it to your browser).

    If the phenomena of the social self, such as intersubjectivity, are correlated with the activity of the cerebral cortex, then we should expect to find characteristic abnormalities in the cerebral cortex of autistic individuals. Maybe you are the one who will discover this!

    Bill Adams

  5. If this intersubjectivity social life theory is correct, I wonder what effect the over use of social media and the vicarious lifestyle through all forms of media has on development. The latest generations are increasingly living in cyber fabricated world. My hypothesis is that a diminished social interaction replaced by social media, and actual experience replaced by a video games reduces the total aggregate learned from experience, thereby reducing intelligence. The vicarious experience can lead to a sense of having those experiences; lacking the total real time interaction with the situations; thereby giving a false self perception of intelligence that doesn't exist.

    I'm no psychologist but I wonder if this could lead to mental disorders, now or down the road. I'm thinking of addictions or sensory deprivation. Or even delusions where a person actual believes they are a pilot, a Marine Sniper, a Guitar Hero, etc.

  6. This is a concern many psychologists have, Andrew. There is not much scientific data yet to say if we should be worried.

    I agree that electronically mediated communications lack the richness and depth of face-to-face encounters, but I am reluctant to say they are inferior, because I'm not sure they replace regular encounters. Maybe they only supplement them.

    I taught college for many years in a stand-up class, then in the last five years, online only. It's a big difference, but the student populations are also different. The online students probably wouldn't be talking to me or to each other at all, if they weren't online. Online doesn't replace other interactions.It adds a new dimension.

    But as more and more communication moves to the electronically mediated sort, perhaps online will displace a significant fraction of face time. What then?

    I think your intuition is plausible. Dominantly online social interaction could lead to delusions and other problems because the physical body is minimized online, and we need our bodies to preserve our social individuality and self-identity. (See my book, The Purpose of the Body. It's on Amazon and

    Good thoughts.

  7. Don't crocodiles have a cerebral cortex they aren't mammals

  8. I think you're right. It's a rare exception to the mammals-only rule. So what does it mean? Logically, it could mean:

    1. Nothing special, if croc cortexes are an entirely different kind than mammalian, OR,

    2. Crocodiles have a much richer sense of social empathy than previously thought. I don't know anything about crocodile social behavior but wouldn't it be interesting if they were as empathic among themselves as, say, elephants or chimps?

  9. Since this is called "stray-ideas" :) what I'm about to suggest might be way out there so bear with me. It's just a quickly-formed thought but I want to write it down before it flutters away.

    So this idea that the cerebral cortex might be responsible for the social self and problems with development in that area of the brain perhaps leading to autism has me intrigued. Recent studies have indicated that the age of the father (not scientifically unproven notions like vaccines) are possibly responsible for the increased occurence of autism in our society. People are putting off marriage and having children later and later in life. There is no correlation with the age of the female because she is born with all the first-generation eggs that she will ever produce. So, her genetic material is always the original master, so to speak. Whereas with sperm, a man makes a copy of a copy of a copy over the course of his lifetime. We all know what that looks like if you make a photocopy on a Xerox and then copy that copy and so on. So why would any problems with the "bad copy" of older genetic material from the father typically only manifest itself in the form of autism in his offspring? This leads me to my not-well-thought-out hunch which I'm sure even the most feeble biologist can shoot down :) Here we go...

    What if the genetics involved with making this "magical" part of the brain known as the cerebral cortex is just... highly fragile? In other words, the stuff that makes lungs and a heart and all the other fundamental organs that nearly all animals on this planet share is pretty much rock-solid, deep, almost bullet proof genetic stuff. I mean, that stuff might even have redundancy in the DNA to ensure it comes out working right. On the other hand, the brand spanking new, super complex recipe that genetically weaves something as elegant (and perhaps fragile?) as the cerebral cortex is probably subject to failure if even any tiny little ingredient in that recipe is spoiled.

    I know this thought is way out there (and again, it's a bit fresh and I haven't thought it through that much yet) but I'm just trying to make sense of why "bad" data from an older male would have a statistically significant impact on causing autism in children, as opposed to other physical maladies.

  10. Interesting thought, Anon., although it does presuppose a causal link between the cortex and social empathy, e.g., Brain causes empathy. As you know, correlation is not causation. All we can legitimately surmise is that cortex activity and social empathy might be correlated. Which one causes the other, or if some third factor causes them both, we cannot say.

    Still, I like your idea, that IF there is a correlation between the structure/function of the cortex and autism, then the cause of that cortextual abnormality might be developmental. It's a plausible idea.

    I think another reason for the rise in autism diagnoses in America recently is increased awareness of the condition. When I was an undergraduate, I was taught that autism was childhood schizophrenia. When I was in grad school, they told me it was a brain disorder. We now know there are significant genetic components to it.

    The latest DSM-V psychiatric manual says that autism is a whole spectrum of disorders that range from mild Asperger's syndrome (has trouble understanding others' emotions), to profound disability, with everything in between. As medical and psychological professionals (and parents) have become more attuned to the disorder, it shows up more in diagnoses.

    None of that says that your hypothesis is wrong, though.

  11. Good points and as you mention, always looming over any statistical chart about the increase of certain disorders is that it was never properly diagnosed in the past or called something else entirely. I think I remembered reading once upon a time that nearly any terrible looking skin disorder was called "leprosy" as opposed to the condition specifically caused by mycobacterium leprae, e.g. psoriasis, eczema, skin cancer, etc. might have been mislabeled as such by the uneducated observer.

    Thanks for your previous response.

  12. Stopped reading here:

    "According to the principles of science, it is not actually possible. No physical activity can produce any nonphysical effect (energy is “physical”) like a thought."

    What a stupid thing to say.