What is consciousness? Yes, in fact, everything. It’s a melody stuck in my head, the sweetness of a chocolate bar, the throbbing pain of a toothache, the wild love, the knowledge that all the senses ever go out. The origin and nature of these experiences, sometimes called Qualia, have been a mystery from the very first days of antiquity to the present day. Many modern philosophers, analyzing the mind, including Daniel Dennett of Tufts University, consider the existence of consciousness as such a blatant insult to the senseless universe from matter and emptiness, which is declared an illusion. That is, they either deny the existence of Qualia, or argue that science will never understand this.
If this statement were true, we would not have anything to talk about. All that needs to be explained to Krzysztof Koch, who wrote this essay, is why you, I and all the rest are firmly convinced that we still have feelings. However, the belief that pain is an illusion, this pain will not diminish. So, there must be another solution to the problem of body and mind. Further – from the first person.
Most scientists accept consciousness as a given and strive to understand its connection with the objective world described by science. More than a quarter of a century ago, Francis Crick and I decided to postpone philosophical discussions on the subject of consciousness, which attracted scientists since Aristotle’s time, and to look for his physical imprints. What happens to an excited area of brain matter that gives birth to consciousness? As soon as we understand this, we will approach the solution of a more fundamental problem.
We are looking, in particular, for the neural correlates of consciousness (NCC), defined as minimal neural mechanisms, which will be sufficient for any particular conscious experience. What should happen in your brain so that you experience a toothache, for example? Should some nerve cells vibrate at a certain magical frequency? Do I need to activate some special “neurons of consciousness”? In which areas of the brain should these cells be located?
Neural correlates of consciousness
When determining the NCC, it is important to understand where the minimum is. The brain as a whole can be considered an NQT: it generates experience from day to day, non-stop. But the location of the consciousness can be further fenced. Take, for example, the spinal cord – a long and flexible “hose” with neurons squeezed into the bone, with a billion nerve cells. If the spinal cord is completely damaged in the process of trauma in the neck, the person paralyzes in the legs, arms and trunk, he can not control the intestine and bladder and lose body sensation. But such paralyzed people continue to enjoy life in all its diversity – they see, hear, smell, experience and remember everything as it was before the sad incident. Only they can not walk, well, they defecate at will.
Or let’s look at the cerebellum, the “little brain” under the back of the brain. This is one of the most ancient brain circuits from the point of view of evolution, involved in controlling movement, posture, gait and complex sequences of movements. Playing the piano, printing, dancing on ice or climbing – all this activity is determined by the work of the cerebellum. It contains magnificent neurons – Purkinje cells, which have antennae and which propagate like sea corals and have complex electrical dynamics. Also, most neurons, about 69 billion, are four times larger than the rest of the brain taken together.
What happens to consciousness if the cerebellum is partially damaged by a stroke or under a surgeon’s knife? Never mind. Patients with a damaged cerebellum complain of some deficiencies, do not play piano so well or type on the keyboard, but they never lose any aspects of consciousness. They hear, see and feel themselves perfectly, retain self-esteem, remember the events of the past and continue to project themselves into the future. Even birth without a cerebellum does not have a strong influence on the conscious experience of the individual.
It turns out that the huge cerebellar apparatus has nothing to do with subjective experience. Why? Important tips can be found in his circuit, which is extremely homogeneous and parallel (just as the batteries can be connected in parallel). The cerebellum works quite straightforward: one set of neurons affects the next one, and the one passes the baton to the third. There are no complicated feedback loops, which are reflected in the passing electrical activity. (Given the time needed to develop conscious perception, most theorists believe that it should include feedback loops in the cavernous circuits of the brain). In addition, the cerebellum is functionally divided into hundreds or more independent computational modules. Each of them works in parallel, with separate, non-overlapping inputs and outputs, controlling the movements of various motor or cognitive systems. They interact weakly – and consciousness, on the contrary, requires the mutual involvement of many systems.
One important lesson we learned from studying the spinal cord and the cerebellum is that the genie of consciousness does not appear whenever any nervous tissue is excited. Need more. This additional factor occurs in the gray matter that makes up the famous cortex of the brain, its outer surface. It is a laminated sheet of complex, interconnected nervous tissue, the size and width of a 14-inch pizza. Two such sheets, repeatedly folded, together with their hundreds of millions of wires – a white substance – are tightly packed into the skull. Everything says that neocortical tissue gives birth to feelings.
You can further narrow the location of consciousness. Let us take, for example, experiments in which different stimuli act on the right and left eyes. Suppose the left eye looks at Donald Trump, and the right eye on Hillary Clinton. One could imagine that a person would see the superposition of Trump and Clinton. In reality, you will see Trump a few seconds, after which he will disappear and Clinton will appear. Then she disappears and Trump returns. Two images will change each other endlessly because of binocular rivalry – the war between the eyes for primacy. Since the brain receives a dual input, it can not choose between Trump and Clinton.
If, at the same time, you lie in a magnetic scanner that registers brain activity, the experimenters will find that a wide range of cortical areas – the posterior parietal cortex – will play a significant role in tracking what we see. What is noteworthy, the primary visual cortex, which receives and misses the information it receives from the eyes, does not signal what the subject sees. The same division of labor is valid for sound and touch: the primary auditory and primary somatosensory cortex does not directly affect the contents of the auditory or somatosensory experience. Instead, the process includes the next stage – in the active zone of the posterior parietal cortex – which gives rise to conscious perception.
More light sheds two clinical sources of cause and effect: electrical stimulation of the cortical tissue and the study of patients after the loss of specific areas in the process of injury or illness. For example, before removing a brain tumor or a locus of epileptic seizures, neurosurgeons map the functions of the proximal tissues of the cortex, directly stimulating it with electrodes. Stimulating the posterior hot zone can cause a stream of different sensations and feelings. These can be flashes of light, geometric shapes, grimaces, auditory or visual hallucinations, a sense of deja vu, a desire to move a certain limb, etc. Stimulating the anterior part of the cortex is quite another matter: on a larger scale, it does not cause any direct experiences.
The second source of information is the patients of neurologists from the first half of the 20th century. Sometimes surgeons had to cut out a large belt of the prefrontal cortex to remove tumors or to alleviate epileptic seizures. It is remarkable how unusual these patients are. The loss of part of the frontal lobe had some harmful consequences: the patients developed reluctance to restrain unacceptable emotions or actions, a lack of motor skills, uncontrolled repetition of actions or words. However, after the operation, they became better and they continued to live without any signs of loss or deterioration of conscious experience. Conversely, the removal of even small areas of the posterior cortex where hot zones were located could lead to a whole class of problems with consciousness: patients could not recognize faces, recognize movements, colors, or orient themselves in space.
Thus, one would think that the views, sounds and other sensations of life that we are experiencing are born in the areas of the posterior cortex. As far as we can judge, almost all conscious experiences appear there. What is the fundamental difference between these posterior regions and most of the prefrontal cortex, which does not directly affect the subjective contents? We do not know. However, the recent discovery indicates that neurobiologists may be close to unraveling.
The counter of consciousness
Medicine needs a device that can reliably detect the presence or absence of consciousness in people with incapacitated or with disabilities. During surgery, for example, patients are immersed in anesthesia to remain immobile and with stable blood pressure – this allows them not to feel pain and not to acquire traumatic memories. Unfortunately, this goal can not be achieved: every year, hundreds of patients somehow remain conscious in anesthesia.
Another category of patients who have severe craniocerebral trauma due to an accident, infection or severe poisoning can live for years, unable to speak or respond to oral requests. Imagine an astronaut floating in space who listens to the control center, trying to contact him. His damaged microphone does not transmit a voice and it seems completely detached from the world. Similarly, patients with a damaged brain that do not allow them to communicate with the world, feel the extreme form of solitary confinement.
In the early 2000s, Giulio Tononi of the University of Wisconsin-Madison and Marcello Massimini of the University of Milan in Italy invented the zip-zap technique, which allows to determine whether a person is conscious or not. Scientists put a coil of wires on the skull and “shoot” it – send a powerful pulse of magnetic energy into the skull, briefly inducing an electric current in the neurons. This intervention, in turn, excites and inhibits the partner cells of the neurons in the connected regions, the wave sweeps through the brain until it dies. The EEG sensor network, located outside the skull, reads these electrical signals. Deploying with time, these tracks, each of which corresponds to a specific place in the brain under the skull, add up to the picture.
This picture shows no regularities, but it is not entirely random. It allows you to determine how much the brain is free of consciousness, according to the rhythms. Scientists quantify these data, compressing them into an archive with the usual .zip algorithm, and get the complexity of the brain reaction. Volunteers who woke up had an “index of perturbation complexity” between 0.31 and 0.7, which fell below 0.31 with deep sleep or anesthesia. Massimini and Tononi tested their method on 48 patients who had brain damage, but who were responsive and awake, and found that in each individual case the method makes it possible to determine the presence of consciousness in a person.
The group then applied the method to 81 patients who were minimally conscious or were in a vegetative state. In the first group, which showed some signs of non-reflexive behavior, the method accurately determined 36 people in consciousness out of 38. Two patients he erroneously labeled unconscious. Of the 43 patients in the vegetative state who did not respond at all, 34 were labeled unconscious, but 9 were conscious. Their brains responded similarly to the brains of those who were conscious, and so they were conscious, but could not tell their loved ones about it.
Current research aims to standardize and improve the “zip-zap” method for neurological patients and extend it to patients of psychiatrists and pediatricians. Sooner or later, scientists will discover a certain set of neural mechanisms that generate some conscious experience. Although these findings will have important clinical implications and help families and friends, they will not be able to answer fundamental questions: why are these neurons, and not the ones? Why on this frequency, and not on that? The mystery that stirs all is how and why any organized pieces of active substance give rise to conscious sensations. After all, the brain, like any other organ, obeys the same laws of physics as the heart and the kidneys. What makes them different? What kind of biophysics turns the gray mass, gray matter into a grandiose technicolor and the richness of sound that our everyday experience of communicating with this world is endowed with?
Ultimately, we need a satisfactory scientific theory of consciousness, which predicts under what conditions any individual physical system – be it a complex scheme of neurons or silicon transistors – begins to experience in the literal sense of the word. Why the quality of these experiences will be different? Why is the clear blue sky so different from the screech of a badly tuned violin? Is there a function for these differences in experiences, and if so, which? Such a theory will allow us to determine what experiences will be in a single system. Before its appearance, any talk about machine consciousness will be based solely on our intuition, which, as scientific history shows, is an unreliable conductor.
A particularly fierce debate erupted around the two most popular theories of consciousness. One of them is the theory of global neuron space (GNW), developed by the psychologist Bernard Baars and neuroscientists Stanislas Dehan and Jean-Pierre Shangyou. The theory begins with the postulate that when you realize something, many different parts of your brain access this information. If, on the other hand, you act unconsciously, the information is localized in a specific sensory-motor system participating in the process. For example, when you quickly type, you do it on the machine. To ask you how you manage it and you will not be able to answer: you have almost no conscious access to this information, and it turns out to be concentrated in the brain circuits that connect your eyes with the rapid movement of your fingers.
In the direction of the fundamental theory
According to GNW, consciousness arises from a certain type of information processing – familiar from the early days of artificial intelligence, when specialized programs have access to small, separated repositories with information. Regardless of the data recorded on this “board”, various auxiliary processes became available: working memory, language, scheduling module and so on. According to GNW, consciousness arises when incoming sensory information recorded on such a board is widely broadcast to different cognitive systems – which process this data for conversation, preservation, remembrance or action.
Since there is not much room on this board, we can not simultaneously realize so much information. The network of neurons transmitting these messages is believed to be in the frontal and parietal lobes. Once the sparse data is translated into networks and made available globally, the information becomes aware. That is, the subject realizes it. Although modern machines have not yet reached this level of cognitive complexity, it is only a matter of time. GNW implies that the computers of the future will be conscious.
The integrated information theory (IIT) developed by Tononi and his colleagues, including myself, has a completely different starting point: the experience itself. Any experience has certain essential properties. It is internal, exists only for the subject as for the “owner”, it is structured (the yellow bus brakes before the dog running across the road), it is specific – it can be distinguished from another conscious experience, as a separate frame in the film. In addition, it is single and definite. When you sit on a park bench in a warm, lovely day, watching the children play, different parts of this experience – the breeze singing in your hair, the joy of your baby’s laughter – can not be divided into parts without losing the fullness of this experience.
Tononi postulates that any complex and interrelated mechanism whose structure encodes a multitude of cause-effect relationships will have these properties – and therefore will have some level of consciousness. If, as a cerebellum, this mechanism lacks integration and complexity, it does not realize anything. According to IIT, consciousness is an internal cause-and-effect force, which has complex mechanisms like the human brain.
The IIT also predicts that complex modeling of the human brain working on a digital computer can not be conscious – even if it talks in such a way that it is not distinguishable from a real person. Just as modeling a massive gravitational pull of a black hole will not deform space-time around the computer, programming consciousness will never create a conscious computer.
There are two tasks before us. One of them is to use more and more sophisticated tools, to observe and explore neurons, to search for consciousness in these neurons. Tens of years will pass, taking into account the Byzantine complexity of the central nervous system. Another challenge is to confirm or disprove the two dominant theories. Or to create a better one on the fragments of these two and explain how a one and a half kilogram organ gives us the fullness of sensations.