Causes of loss of consciousness
Loss of consciousness is a mild form of acute cerebrovascular insufficiency, i.e. These conditions are primarily caused by a lack of blood flow to the brain. During attacks with loss of consciousness, disturbances in nervous activity occur, which is also accompanied by a decrease or complete cessation of the body’s response to the person’s perception of his own body, as well as external stimuli.
“I’m losing consciousness” is a fairly common complaint in the doctor’s office. There are many reasons for this condition. All the causes of such conditions are connected by a common characteristic - brain damage, which can occur for various reasons:
- direct impact. This category of causes includes head injury, poisoning, hemorrhage, electrical trauma and much more;
- indirect effects, which include heart disease, shock, fainting, bleeding, etc.
Often people lose consciousness when overheated (under the hot sun, in a bathhouse, etc.) or hypothermia. In addition, loss of consciousness can occur when there is a lack of oxygen in the body due to suffocation, poisoning, etc. Another cause of this condition may be metabolic disorders, which can occur with diabetes or fevers.
Sometimes patients turn to doctors saying that they suddenly began to lose consciousness. But it is worth remembering that this condition does not arise suddenly. For example, if a grandmother suddenly says that her grandson began to lose consciousness, most likely she did not notice or did not pay attention to any symptoms. At the first stage, an attack occurs without loss of consciousness, which is manifested by severe weakness, yawning, ringing in the ears, lightheadedness and nausea, a feeling of emptiness in the head, dizziness, darkening of the eyes, cold sweat, etc. In addition, a person may experience slight numbness in the limbs, as well as increased bowel function.
During attacks, a person gradually begins to turn pale, and his pulse weakens, blood pressure drops, his eyes first wander and then close, after which loss of consciousness occurs. The attack itself lasts on average about 10-15 seconds, although its duration may be longer. During attacks accompanied by loss of consciousness, muscle tone weakens, causing the person to fall.
After the attack ends, the person gradually comes to his senses, but remains anxious for some time, after which both the pulse and breathing return to normal. Often after an attack, the patient continues to suffer from headache, malaise and weakness for some time.
What is consciousness?
Consciousness is everything you experience. It's the melody stuck in your head, the sweet taste of chocolate mousse, the throbbing toothache, the immense love for your child and the bitter knowledge that eventually all feelings will disappear.
From ancient times to the present day, the origin and nature of these experiences, sometimes called qualia, have been shrouded in mystery. Many in contemporary analytic philosophy of mind—perhaps led by Daniel Dennett of Tufts University—see the existence of consciousness as such an intolerable affront to reality, which they see as a meaningless material universe and emptiness. that they declare it an illusion. That is, from their point of view, qualia either do not exist or are inaccessible to scientific research.
If this statement were true, my essay would be very short. I would just have to explain why you, I and most other people are firmly convinced that we have feelings. However, with a tooth abscess, no argument, even the most sophisticated, in favor of the illusory nature of my pain will reduce my suffering one iota. Since attempts to solve a psychophysical problem with desperate reasoning of this kind do not arouse my sympathy, I will go further.
Most scientists accept consciousness as a given and strive to understand its connection with the objective world that science talks about. More than a quarter of a century ago, Francis Crick and I decided to put aside the philosophical discussions of consciousness (which have been going on since at least the time of Aristotle) and instead look for its physical traces. What happens in the very sensitive part of the brain that gives rise to consciousness? By understanding this, we may be able to move closer to solving a more fundamental problem.
We are looking in particular for the neural correlates of consciousness (NCC), defined as the elementary neural mechanisms that are collectively sufficient to produce any given experience. What, for example, must be happening in your brain for you to feel a toothache? Maybe some nerve cells should vibrate at some magical frequency? Or maybe some special “neurons of consciousness” need to be activated? In what areas of the brain are these cells located?
Neural correlates of consciousness
When defining NKS, the word “elementary” plays an important role. After all, the entire brain can be thought of as the neural correlate of consciousness: it is constantly generating experiences, day after day. But the location of consciousness can be delineated more strictly. Consider the spinal cord, the flexible, foot-and-a-half-long tube of neural tissue that runs through the spine and contains about a billion nerve cells. An injury to the neck that cuts off the connection between the spinal cord and the brain paralyzes the limbs and torso, renders them unable to feel, and also deprives the victim of the ability to control the bowels and bladder. And yet, in the experiences of these tetraplegics, all the diversity of life is completely preserved: they see, hear, smell, react emotionally and remember as well as they did before the tragic incident that radically changed their lives.
Now let's look at the cerebellum - the "little brain" in the lower back part of the brain, one of its most ancient autonomous parts. The cerebellum is involved in the control of motor skills, posture and gait, and is responsible for the smooth execution of complex sequences of motor movements. Playing the piano, typing, ice dancing, rock climbing - all these activities are associated with the cerebellum. It contains Purkinje cells, the brain's most stunning neurons, which, thanks to their luxurious tendril dendrites, resemble fan corals and harbor complex electrical dynamics. And in general: the cerebellum has a huge number of neurons, about 69 billion (most of which are stellate granule cells), which is four times more than in the rest of the brain combined.
What happens to consciousness when the cerebellum is damaged as a result of a stroke or surgery? Very little! Patients with cerebellar damage report loss of some skills, such as fluent finger movements when playing the piano or typing, but never complain of loss of awareness. Their vision, hearing and other types of sensitivity work perfectly, they maintain self-control, remember the past and make plans for the future. Even being born without a cerebellum does not have a significant effect on the individual's consciousness.
The entire huge cerebellar apparatus has no relation to subjective experiences. Why? Its diagram provides important clues. Uniformity and parallelism reign here (exactly the same as when batteries are connected in parallel). Essentially, the cerebellum is a feedforward circuit: one group of neurons influences another, which, in turn, influences a third. There is no complex feedback system reacting to electrical impulses going back and forth. (Given the time it takes for consciousness to form a sensation, most theorists conclude that feedback loops in the brain's cavernous circuitry must be involved in this process.) In addition, the cerebellum is functionally divided into hundreds, if not thousands, of independent computational modules. Each of them operates in parallel, has different, non-overlapping inputs and outputs, and controls the movements of different motor or cognitive systems. These modules practically do not interact, and the interaction of circuit elements is necessary for consciousness.
An important lesson to be learned from our review of the features of the spinal cord and cerebellum is that not every nervous tissue is capable of creating sensations when excited. The genie of consciousness has his own special lamp. As we found out, the role of the magic lamp is played by the gray matter of the surface of the brain, its famous cortex. The cerebral cortex is a laminated layer of intricately interacting nerve tissue, about the size of a 14-inch pizza. Two extremely wrinkled hemispheres with their hundreds of millions of wires (white matter) are squeezed into the cranium. All the facts available to scientists indicate that sensations are created by the neocortex.
We can delineate the location of consciousness more precisely. Let us turn to experiments in which different stimuli are presented to different eyes - right and left. Let there be two different images in your field of vision - Donald Trump and Hillary Clinton, and the first image is visible only to the left eye, and the second - only to the right. A strange superposition of Trump and Clinton arises in the mind. It is indeed unusual: Trump is visible for a few seconds, then he disappears and Clinton appears, who in turn disappears so that Trump can reappear. In what neuroscientists call binocular rivalry, two images follow each other in an endless dance. Because the brain receives ambiguous information, it cannot decide whether it is dealing with Trump or Clinton.
During this experiment, if you lie inside an MRI scanner that records your brain activity, the experimenters will find that multiple areas of your cortex are active. Their common name is “posterior hot zone.” These are the parietal, occipital and temporal regions of the posterior cortex [see. figure below], which play a major role in visual tracking. Interestingly, the primary visual cortex, which receives and transmits information from the eyes, does not signal what the subject is seeing. A similar division of labor appears to apply in the auditory and tactile cortex: the respective types of primary cortex (primary auditory and primary somatosensory) do not directly contribute to the content of auditory or somatosensory experiences. Consciousness perceives images, including the images of Trump and Clinton, thanks to the activity of not the primary, but the posterior cortex, or more precisely, its hot zone.
Two clinical sources provide a clearer picture of these cause-and-effect relationships: electrical stimulation of cortical tissue and studies of patients who have lost parts of the cortex due to injury or disease. For example, before removing a patient's brain tumor or epileptic seizure area, neurosurgeons map the functions of nearby cortical tissue by directly stimulating it with electrodes. Stimulation of the posterior hot zone produces a wide variety of experiences. These can be flashes of light, geometric shapes, distorted perception of faces, auditory and visual hallucinations, a feeling of triviality or unreality of what is happening, the urge to move a limb, and so on. Stimulation of the anterior cortex is a completely different matter: by and large, it does not directly cause any experience.
Another source of important information comes from neurological patients in the first half of the twentieth century. Surgeons sometimes had to cut out an entire belt of prefrontal cortex to remove tumors or ease epileptic seizures. It is noteworthy that the behavior of the operated patients turned out to be unremarkable. The loss of part of the frontal lobe did have certain negative consequences: patients ceased to control inappropriate emotions and actions, they had problems with motor skills, and involuntary repetition of certain actions and words was noted. However, after the operation, their personality traits and IQ improved, they continued to live for many years, and there was nothing to suggest that the radical removal of frontal tissue significantly affected their consciousness. But the removal of even small areas of the hot zone of the posterior cortex is fraught with the loss of entire classes of experiences: patients are not able to recognize faces, record movement, perceive colors and space.
So, apparently, visual, auditory and other images of the events we experience are generated by areas of the posterior cortex. As far as one can tell, almost all experiences arise there. What prevents most of the prefrontal cortex from having the same direct relationship to subjective content that the posterior hot zone has? Alas, we don't know. Well, let! After all, a recent discovery by neuroscientists seems to bring us closer to an answer to this question, and it is breathtaking.
Dimension of consciousness
In medicine, there is an unmet demand for a device that can clearly record the presence or absence of consciousness in people who are in a weakened state or completely incapacitated. For example, anesthesia is used during surgery. It is needed so that the patient does not move or feel pain, so that his blood pressure is stable and so that he is not subsequently tormented by unpleasant memories. Unfortunately, it is not always possible to achieve all this: every year hundreds of patients, while under anesthesia, remain partially conscious.
And there are also patients with serious brain damage resulting from an accident, an infectious disease or acute intoxication. They can live for years and years without being able to speak or answer verbal questions. It can be very difficult for doctors to determine whether such patients are experiencing distress. Imagine an astronaut flying in space who hears the mission control center trying to contact him, but cannot answer because, due to a breakdown, his intercom works only for reception. The astronaut found himself lost to the world. The same hopeless loneliness is experienced by a patient whose damaged brain prevents him from communicating with the world. This is an extreme form of solitary confinement.
In the early 2000s, Giulio Tononi of the University of Wisconsin-Madison and Marcello Massimini, now at the University of Milan, Italy, pioneered the use of zap technology. and zip" to determine the presence or absence of consciousness. This is done like this: an inductance coil is applied to the scalp and “bang” (zap) - sending a powerful magnetic impulse to the skull, inducing a short-term electric current in nearby neurons of the brain. In turn, the induced current excites and suppresses the partner cells of these neurons, penetrating the circuit into neighboring areas. Until they completely fade out, the waves of electric current have time to pass throughout the entire cortex. Sensors placed on the head record this process in the form of an electroencephalogram. The result is a movie that shows how electrical impulses are generated in different places in the brain over time.
The records obtained in this way do not demonstrate any stereotypical pattern, but these data cannot be called completely random. An interesting point is this: the more predictable the propagation of electrical waves, the greater the likelihood of absence of consciousness. By using an information compression algorithm used to archive computer files (zip), the identified relationship was presented quantitatively. This is how researchers have learned to assess the complexity of the brain's response. In volunteers, when they were awake, the perturbational complexity index (PII) took values from 0.31 to 0.70, and when they were in a state of deep sleep or under anesthesia, it dropped below 0.31. Massimini and Tognoni tested the zap and zip technology on 48 awake patients who had brain damage but responded normally to questions. The researchers found that in each of the 48 cases, the resulting COI confirmed behavioral evidence of consciousness.
This team of scientists then tested the technology on patients, some of whom showed minimal glimpses of consciousness, while others were completely in a vegetative state (a total of 81 people). For the first group (with glimpses of non-reflexive behavior), the presence of consciousness was correctly established in 36 cases out of 38. Only two patients in this group were mistakenly identified as unconscious. Of the 43 patients in a vegetative state (all attempts to establish communication with them failed), the absence of consciousness was diagnosed in 34. The brains of the nine others reacted in the same way as in the presence of consciousness. Perhaps these patients are among those who are capable of consciousness, but are not able to communicate even with people close to them.
Researchers are now seeking to improve and standardize zap and zip technology for neurological patients, and to extend its use to patients treated by psychiatrists and pediatricians. Scientists will sooner or later find out what neural mechanisms give rise to experiences, which will significantly affect the development of medicine and will probably alleviate the plight of many people whose relatives and friends have severe brain damage. However, a number of fundamental questions remain. Why these neurons and not those? Why this particular frequency and not another? Where is the answer to the question of how and why a highly organized piece of active matter gives rise to consciousness? This is truly an eternal secret! Well, in fact: the brain, like any other organ, obeys physical laws - the same as the heart or liver. What's the difference? What feature of the biophysics of a piece of excitable brain matter allows it to transform gray mucus into the magnificent surround sound and equally magnificent moving variety of colors from which our everyday experiences are woven?
Ultimately, we need a solid scientific theory of consciousness that can answer the question of under what conditions a physical system—whether a complex chain of neurons or silicon transistors—generates experiences. In addition, this theory should have answers to other questions. Why are experiences of different quality? Why does a clear blue sky feel so different from the screeching sound of a poorly tuned violin? Does this kind of difference in sensations have any function, and if so, what is it? With a solid theory of consciousness, we will be able to predict verifiably in which cases the systems we create will be experiencing. While there is no such theory, we have to talk about the topic of machine consciousness, relying only on intuition, and, as the history of science testifies, it is not a reliable assistant.
There are two theories of consciousness that are most widely known today, and both are hotly contested. One of them is the theory of the global neural workspace (GNW) by psychologist Bernard J. Baars and neuroscientists Stanislas Dehaene and Jean-Pierre Changeux. What led to this theory was the following observation: when you act consciously, information about that action is accessed by many areas of your brain, but when you act unconsciously, the information is localized within the specific sensorimotor system you are using. For example, you do typing quickly automatically, and if you are asked how you do it, you will not be able to answer: information about this process mostly passes by your consciousness, being localized in the neural circuits that connect your eyes with fluent finger movements.
On the way to a fundamental theory
Consciousness, the GNW theory claims, is the product of a certain type of information processing - the same one that found application in the first artificial intelligence systems, where all specialized programs had access to a common modest storage of information. Any data that appeared on this “board” immediately became available to the device responsible for working memory, language, planning, or some other second-level functional module. According to GNW theory, consciousness arises when sensory information received on such a board is globally transmitted to multiple cognitive systems that process this data to speak, remember, recall or act.
Because space on the board is limited, we can only be aware of a small amount of information at any given time. Scientists suggest that the network of neurons that transmit these messages is located in the frontal and parietal lobes of the brain. When this meager data is broadcast on this network and made available globally, the information is realized. That is, it falls into the field of consciousness of the subject. Although modern machines have not yet reached this level of cognitive complexity, it is only a matter of time. Computers of the future, the GNW theory argues, will be conscious.
What led to integrated information theory (IIT), developed by Tononi and his collaborators, including myself, was a completely different observation: the experiences themselves. Every experience has certain essential properties. It is intrinsic, existing only for the subject as its “owner”; it is structured (a yellow taxi brakes so as not to hit a brown dog crossing the road); and it is specific—different from any other experience (just as a particular frame of a film is different from all the others). Moreover, it is unified and specific. When you sit on a park bench on a warm, sunny day and watch children play, the different parts of the experience—the breeze that moves your hair, for example, and the joy that comes from your baby's laughter—cannot be separated from each other without turning a given experience into some other.
Tononi postulates that any complex mechanism that has interconnected elements and whose structure encodes a certain set of cause-and-effect relationships has the above properties and, therefore, a certain level of consciousness. Such a mechanism feels the whole world as external to itself. But if, as in the case of the cerebellum, the mechanism lacks integration and complexity, it is not conscious. According to TII, consciousness is an intrinsic causal force associated with such complex mechanisms as, in particular, the human brain.
In addition, what led to the creation of TAI was the complexity of the underlying structure of consciousness of interconnected elements - the non-negative number Φ (pronounced "phi"), which quantifies consciousness. If Φ is equal to zero, this system does not feel its selfhood. On the contrary, if this number grows, the internal causal power of the system, that is, its consciousness, grows. The brain, which has enormous and highly specific connectivity, has a very large Φ number, which means a high level of consciousness. TII explains a number of neurobiological facts, such as why the cerebellum is not directly related to consciousness and why the latter can be measured using zap and zip technology. (This measurement method allows, albeit very roughly, to determine the number Φ).
Among other things, TAI predicts that no matter how carefully a digital computer model of the human brain is created, it will not be conscious, even if it learns to speak exactly like a person. Just as simulating the enormous gravitational pull of a black hole fails to warp the actual space-time around the computer running the astrophysical model, consciousness programming fails to create a conscious computer. Consciousness cannot be calculated: it must be built into the structure of the system.
There are two problems ahead. One of them is to further refine the neural localization of consciousness through the use of increasingly sophisticated tools that make it possible to observe and study the vast coalitions of highly heterogeneous neurons that make up the brain. The Byzantine ornateness of the central nervous system suggests that this work will take decades. Another problem is the verification or falsification of the two currently dominant theories of consciousness. Or, perhaps, the creation of a new, more advanced theory from fragments of the two current ones, which could provide a scientific solution to the main mystery of our existence: how a three-pound organ of our body, the consistency of which resembles bean curd, generates the feeling of life.
