Antonio Damasio is a neuroscientist and neurologist who has published a number of theories about how the brain and mind work. Unlike many theories of mind, his are thoroughly grounded in neuroanatomy.
Central to Damasio’s theory of consciousness is the idea of biological value, that which helps in preserving homeostasis, which of course aids in survival. This survival impulse is shared by all life, even the simplest single celled organisms. Brains are systems evolved to preserve homeostasis and ensure survival.
In Damasio’s view, consciousness centers on the self. While he doesn’t see the self as an illusion, he doesn’t see it as a static thing either, but rather a process evolved to manage homeostasis. He uses the analogy of a symphony. When the symphony begins, it doesn’t have a conductor. But as it plays, the conductor comes into existence and then takes control of the symphony. The self comes into being in the brain in layers: the proto-self, the core self, and the autobiographical self.
The proto-self’s formation begins in the brainstem, although in healthy humans the insular cortex, an area in the fold between the parietal and temporal lobe, is also involved. The brainstem is constantly receiving updates from the body, from the peripheral nervous system. It uses these signals to construct an image map of the body. The lower portions of the brainstem are focused on the viscera: the heart, digestive tract, etc. The higher portions construct an image of the musculoskeletal body.
The brain is vitally concerned with and tightly bound to the body. It is constantly receiving updates of its body image map from every corner of the body proper, initiating various changes, and then receiving the results of those changes in a tight resonance loop with the body that never ends, until death. And the most primal level of this resonance starts in the brainstem.
The brainstem is phylogenetically ancient, and many simple animals get along without much else. From the brainstem arise primordial feelings. It maintains its active model of the body, the chief object of its concern, and has the basic foundations of homeostasis management.
One interesting area of evidence that Damasio uses for this part of the theory are children born with a birth defect: hydranencephaly, that is without a cerebrum, with only a brainstem and hypothalamus. These children have a kind of proto-sentience somewhat similar to normal newborns, although they are never able to move beyond that cognitive stage. Yet they appear to enjoy sensations, music, have favorite caregivers, and generally have a sort of primal existence.
On top of the proto-self is the core self. The core self is the momentary self. It exists in “pulses.” It comes into existence when the proto-self perceives objects and how those objects relate to the body. Is the object food? A predator or some other kind of threat? Another body like ours? Something else?
When I first read Damasio’s description of this core self concept, I wondered what he was talking about? Then I realized that he was addressing primal first person experience, the state of a self experiencing perceptions and what those perceptions immediately mean to the self, to the body. Or perhaps more accurately, he is addressing the feeling of first person experience.
The brainstem is heavily involved in generating the core self, but it isn’t the main show. Damasio hypothesizes that the main coordinator may be the thalamus, but all areas seem to participate, from the brainstem, the thalamus, and the cerebral cortex.
On top of the core self is the autobiographical self. This is the self that comes into existence as the organism lives its life. It is heavily dependent on memories, along with the projections it makes for the future.
And here we get to what I find to be the most interesting aspects of Damasio’s theory. It’s an explanation for how perception, memory, imagination, and decisions get made in the brain. To begin with, Damasio describes two types of brain areas: image making areas, and dispositional areas. The dispositional areas are, evolutionarily, far more ancient, but even the brainstem has low resolution image making portions. We are conscious of a portion of the processing that happens in the image areas, but never conscious of what happens in the dispositional areas.
To understand the image making areas, consider the process of seeing something. The photons hitting the photoreceptors on your retina form a pattern which trigger signals up the optic nerve to the brain. When the signals reach the vision processing centers, patterns form, models, image maps built from the cumulative signals coming in. In other words, visual images form.
If we hear a sound, a similar audio image will be formed in the audio processing centers, and so on for all the other senses. This happens with greater resolution in the neocortex than in the sub-cortical areas, but it happens in many areas of the brain, all in the regions closest to where the sensory pathways come in.
Further from the sensory pathway areas are the dispositional portions. These are the areas that drive memory, imagination, emotions, and actions. For memory, Damasio’s view is that we never store actual images. We only store what the image means to us, the associations between the aspects of the image, the associations between various images from the different senses, and the associations between combinations of images, emotions and possible actions. From these associations, we are able to later recreate a version of the original image, although it’s never as detailed as the original since the recreated version doesn’t have the sensory data stream coming in.
This works through a concept Damasio calls CDZs (convergence divergence zones). When images form, the patterns propagate from the image areas into the dispositional areas. The image of a doughnut may come in at the same time as the smell of doughnuts and then the taste. All of the cascading signals from the senses converge at a certain neural circuit, a zone. If this happens repeatedly, or perhaps once with strong emotions firing, synapses become strengthened.
Later, when only one of these signals come in, it may trigger a reverse signal flow, initiating a process called retroactivation, that causes a version of the patterns that initially formed the convergence to reappear in the image areas. So the smell of doughnuts may trigger memories of the sight and taste of doughnuts.
CDZs exist in hierarchies. The lowest hierarchies receive inputs from image areas and can both output back to the those image areas as well as upstream to next level of CDZs. The CDZ hierarchies are clustered in regions Damasio calls CDRegions, which interconnect with each other. Damasio envisions CDZs existing in the “many thousands”, but there being a few dozen CDRegions.
The multisensory doughnut example above would be a fairly high level CDZ. In reality, every complex image is itself a galaxy of CDZs. The visual of a bear is a full range of associations, such as attributes of the bear’s shape, color, activity, etc. The image of the bear that probably popped in your mind while reading the previous sentence was, according to Damasio, recreated from the bear related CDZs in your brain being triggered by the word “bear.”
But CDZs aren’t just for generating images. They also generate actions. (Image generation could itself be considered a type of action.) That action can be to trigger the release of hormones, to initiate muscle action, or maybe to inhibit action arising from another cluster of CDZs. CDZs are, of course, the physical manifestation of associations, and the mind works through associations.
I wasn’t sure of usage rights so I didn’t reproduce them here, but here are some diagrams showing the CDZ hierarchies in action. It starts with a stimulus to part of the network, and ends with the whole associative network being activated and generating the images.
CDRegions are probably created from genetic information, as are many primordial CDZs, but most CDZs get created from experience, from learning.
Incidentally, CDZs also trigger emotions, which Damasio sees as self contained autonomous actions. He makes a distinction that had never occurred to me, the one between having an emotion, and the feeling of the emotion. When something triggers an emotion, it happens. Hormones are released, heart rate is altered, the brain goes into a state prepared for a certain type of cognition.
Earlier in evolutionary history, this immediately led to action, but in more intelligent animals it’s a two step process. The second step for us is that we feel the emotion though the body image, which influences our inclinations, but leaves us with the power to alter the inclined actions, a capability the autobiographical self contributes toward and a possibly adaptive reason for its existence.
The CDRegions interlink with each other, but the linking appears to converge heavily in a region Damasio calls the PMCs (posteromedial cortices), an unusual name referring to a region that, judging by his diagrams, appear to be in the middle portions of the parietal lobe, and the posterior cingulate cortex underneath. It is here that Damasio thinks the autobiographical self may live. It might be best thought of as a CDRegion at the center of a galaxy of CDRegions.
There’s obviously a lot here, and I’ve just given a very surface level summary. As I noted above, I find the CDZ and CDRegion part of this theory to be the most interesting. (In reality, they were published as a separate theory, predating Damasio’s theories of self by several years, or at least their publication.) The power of the CDZ and CDRegion concepts are that they may give us insights into the architecture of the mind.
One possible flaw I see in this overall framework is that it’s more a theory of self than of consciousness in particular. It doesn’t seem to address the difference between what happens in our conscious experience and what happens subconsciously, or of the experience of experience. (There are other scientific theories that do, and they’re not necessarily incompatible with Damasio’s theories.)
I also suspect that the division between image forming areas and dispositional areas in the brain isn’t nearly as clean as Damasio implies. It’s almost certainly more of a spectrum, with early sensory cortices perhaps being more image forming and other regions gradually becoming more dispositional the further they are from the sensory pathways.
There’s also a danger here of viewing the images as passively created by the senses, when in reality, particularly for vision, an enormous amount of active modeling is taking place from the retina on back to the brain, with even our immediate perceptions heavily influenced by preexisting associations.
Still, there’s a lot here that strikes me as very plausible. Damasio makes no pretense of his theories being the final word, only that they add possible explanations of what is happening, and I think they definitely do that.
All of the information in this post came from Damasio’s book ‘Self Comes to Mind‘. A quick warning: I didn’t find this to be easy reading. Damasio often discusses neuroanatomy in detail and assumes the reader can follow along. And his style is very verbose, often taking a long time to make a fairly basic point. Still, if you’re interested in how the mind works, I found it worth the effort.
If you have the time, here’s Damasio’s TED talk on consciousness:
h/t amanimal for recommending the book!