We Are Our Brains

by D. F. Swaab

  “Absence seizures” are a form of epileptic seizure in which there’s a break in consciousness for around five to ten seconds. During that time, patients look blank and don’t respond. They often blink their eyes and smack their lips. Their awareness is impaired, and their frontoparietal networks (fig. 1), crucial to consciousness, are much less active. In complex partial seizures, sometimes lasting several minutes, consciousness is also impaired. Patients are awake but can no longer respond. They make automatic movements with their hands and mouths, and frontoparietal activity is again much reduced. These changes in activity in the cerebral cortex aren’t found in patients with temporal lobe epilepsy whose consciousness isn’t impaired (see chapter 15).

  Indeed, the distinction between a vegetative state and minimal consciousness revolves around the functioning of the frontoparietal network. In the former case, the network is disconnected. In the latter, speech and complex auditory stimuli do spark general activity of the network that is crucial to consciousness, as shown in fMRI and PET studies. This also means that in principle, an entire network can be recruited in these patients, as was shown in the case of the minimally conscious man who was aroused when his thalamus was electrically stimulated using brain electrodes. It’s claimed that music or electrical stimulation of a nerve in the arm (the median nerve) can speed up the process of reviving someone from a state of minimal consciousness, but very few controlled studies have been done, and so far there have been no spectacular results.

  ILLUSIONS AND LOSS OF SELF-CONSCIOUSNESS

  The “I” is the body’s rather untrustworthy partner, which cheats on it whenever it gets a chance.

  Victor Lamme, There’s No Such Thing as Free Will, 2010

  For self-consciousness you need a combination of sensory input and an intact cerebral cortex. The premotor cortex is important for the feeling that a certain body part belongs to us. It is there that various types of sensory information, like input from eyes, ears, organs of balance, muscles, tendons, and joints (proprioception) and the sense of touch are put together. You can fool your premotor cortex with the following little trick. Put a rubber hand on the table where your own hand would be, meanwhile putting your hand under the table where you can no longer see it. If someone then repeatedly strokes the rubber hand and your own hand at the same time, your brain combines the sight of the rubber hand being stroked with the sensation of your real hand being stroked. After about ten seconds you begin to regard the fake hand as your real one. If someone suddenly hits the rubber hand with a hammer you jump out of your skin. It seems that the combination of touch (coming from your own, hidden hand) and visual information (coming from the fake hand) is needed for the illusion that this is your real hand. Scans of people experiencing this illusion show activity in the premotor cortex and cerebellum. The feeling that a body part belongs to you appears to be based on nothing more than the activity of the few groups of neurons in a few very specific brain areas.

  Self-consciousness can be impaired or lost for various reasons. In the first stage of Alzheimer’s, around 10 percent of patients aren’t aware of their degeneration. The percentage increases as the disease progresses. This unawareness that something is wrong with you is called anosognosia (from the Greek nosos, “disease,” and gnosein, “to know”). It’s usually the person’s partner who notices that something is wrong and makes them see a doctor. Anosognosia is linked to reduced activity in the angular gyrus, near the upper edge of the temporal lobe (fig. 28). It’s here that sensory information from the body and the surroundings is combined, making this area essential for self-consciousness. This part of the cerebral cortex is increasingly damaged as Alzheimer’s progresses.

  Out-of-body experiences or near-death experiences (see chapter 16) are also caused by a malfunction in the angular gyrus. A lack of oxygen prevents the angular gyrus from integrating the sensory information coming from your body, including the organs of balance, disrupting consciousness of your entire body.

  Building on the rubber hand experiment, the Swedish scientist Henrik Ehrsson induced out-of-body experiences in experiments using cameras linked to a head-mounted video display. The participants were given goggles with a video screen for each eye. The screens showed images from two cameras filming them from behind, so that participants saw a 3-D image of their own back. Ehrsson then used two plastic rods to simultaneously touch a participant’s actual chest and the chest of the virtual body, moving the second rod to where the virtual chest would be according to the camera pictures. This gave participants the illusion that they were in the virtual body, and made their own body appear to be someone else’s. When the virtual body was threatened with a hammer, the participants reacted as if the threat were real. Their fearful attempts to ward off the blow were accompanied by physiological responses (notably the level of perspiration on the skin), showing that their emotions were aroused. In Switzerland, Olaf Blankes carried out similar experiments in which participants watched holographic projections of their own bodies. Afterward he blindfolded them and asked them to walk back to the spot where they had been standing. Participants who had had an out-of-body experience during the experiment walked back to the spot where their virtual bodies had stood. So self-consciousness isn’t a metaphysical construct. Your brain constantly manufactures the sense that your body belongs to you, using sensory information from muscles, joints, vision, and sensation.

  Methods of fooling consciousness can also be used to treat patients with chronic phantom pain, for instance after having had an arm or leg amputated. The neuroscientist V. S. Ramachandran discovered that phantom pain is caused by a conflict in the brain. Each time a patient wants, say, to move their (amputated) hand, they receive a signal back that it is impossible. As a result, the brain ultimately forces the phantom hand into an extremely painful, cramped position. Ramachandran’s solution was as brilliant as it was simple. He placed a mirror perpendicular to his patients’ chests, between their two hands, so that when they stretched out their normal hand and viewed the mirror from that side, it appeared as though both hands were working. The patients were given exercises in which they calmly opened and closed their normal hand while looking at their “phantom hand” in the mirror. Although they knew that it was an illusion, the visual input of a relaxed, calmly moving hand helped their phantom hand to relax and the phantom pain to disappear. One man whose leg had been amputated had been unable to wear his leg prosthesis for eight years due to phantom pain in his stump. After a mere three to four hours of mirror therapy, his pain had gone, and he was able to practice walking on his prosthetic leg for the first time, even though he knew that the leg he had seen move in the mirror no longer existed.

  FIGURE 22. Some specialized cortical areas. (1) Primary sensory cortex, (2) auditory cortex, (3) motor cortex, (4) visual cortex. Also: (5) middle temporal gyrus, (6) superior temporal gyrus, and (7) premotor cortex.

  “FILLING IN” MISSING INFORMATION

  If information enters the cerebral cortex via an abnormal route, the patient isn’t conscious of this fact.

  Alien hand syndrome (see chapter 17) shows that self-consciousness also requires effective communication between the left and right hemispheres of the brain. This syndrome can occur if the bundle of fibers connecting the two (corpus callosum, fig. 2) is damaged. Sometimes surgeons have even deliberately severed this link in a last-ditch attempt to make life bearable for patients with disabling epileptic seizures. After the operation, these patients turned out to have split consciousness. The neurobiologist and Nobel laureate Roger Sperry discovered that one side of the brain wasn’t aware of what the other side was seeing. In an experiment, patients could describe only images that reached the left side of the brain, because the ability to speak is located on that side. However, they seemed unaware of images that reached only the right side of the brain. Yet if they were asked to use their left hand (controlled by the right side of the brain) to indicate the image that had just been shown to the right side of the brain, they could do s
o. So on an unconscious level they had access to information that reached the right side. The left side of the brain then made up a story combining the information from both sides of the brain. The story was logical to the patients but completely incomprehensible to their surroundings. When the right side of the brain registered a written instruction to stand up and walk away, a patient obeyed. When asked why he did so, he didn’t say, “You just asked me to,” because he hadn’t consciously registered the instruction. So he made up a reason to explain his behavior: “I’m just going to get some hot chocolate.”

  The peculiar situation in which a neglect patient finds himself is also often made “plausible” with a great deal of inventiveness and imagination. A paralyzed patient accounted for her situation as follows: “I’d like to get up, but my doctor won’t allow me” (see chapter 7). In fact these kinds of fantasies are based on a very general principle. If the brain doesn’t receive the right information in the expected place, the cerebral cortex at that location will work harder to fill in the gap. Such inventions are perceived as real information (see chapter 10). This phenomenon can also arise when there’s a lack of auditory information, causing people to hear songs nonstop, or of visual information, causing them to see nonexistent objects in dim light. Lack of memory information resulting from alcohol abuse can lead people to make up events constantly without being aware of it, and lack of information from limbs as a result of amputation can cause phantom pain (see chapter 10). Each brain function has its own local system that enables consciousness (fig. 22). It’s due to the differences in the location of increased cortical activity that we “see” things when we lack visual input and “hear” music when we lack auditory input.

  The phenomenon of “blindsight” demonstrates the importance of information following the right route to the right part of the cortex. It was always thought that damage to the left primary visual cortex (fig. 22) would result in total blindness of the right field of vision and the other way around. But when individuals who were perceptually blind in a certain area of their visual field had to guess where a light stimulus was located in that area, they were able to do so correctly to an extent that couldn’t be due to chance. Seeing something without being aware of it is referred to as type I blindsight, or attention blindsight. It was assumed that this unconscious mode of seeing was due to the receipt of visual information in subcortical areas. A new scanning method showing nerve pathways (diffusion tensor imaging) has revealed that individuals with this form of blindsight do receive information in the part of the cerebral cortex where visual information is processed but that it arrives via an abnormal route through the brain. So even though information arrives in the part of the cerebral cortex where it’s normally received, a patient with blindsight isn’t conscious of it, apparently because it travels by an unusual route. This would also explain why neglect patients can see something but not be conscious of it, because the information arrives in the cortex by another route, as a result of the damage caused by their stroke.

  NOTIONS ABOUT THE MECHANISMS OF CONSCIOUSNESS

  Consciousness can be seen as an emergent characteristic generated by the joint functioning of the enormous network of nerve cells.

  Throughout history, many metaphors have been used to describe consciousness of surroundings, like the “Cartesian theater,” “the film in your head,” and “a TV screen.” But they are all based on the dualist notion that there’s a little man in your head watching the images. It is a curious idea, not least because it raises the question of what is in the head of the little man. Another little man? No, we just have an amazing network of neurons.

  John Eccles, who in 1963 won the Nobel Prize for his research into synaptic transmission, simply could not accept the idea that the neural network was responsible for consciousness. Instead he devised a theory (philosophical rather than neurobiological) that the neural units of the cortex were linked to mental units called “psychons.” He believed that these psychons acted on the cortex in “willed” actions and thought and that their common activity gave rise to consciousness as an integrated mental process. No one actually knows what a psychon is. That makes it untestable as a theory and therefore, from a scientific point of view, an unacceptable hypothesis. It is, moreover, entirely redundant. All recent research suggests that the joint activity of enormous numbers of neurons in communication with a number of brain areas provides the foundation for consciousness.

  Consciousness can be seen as an emergent characteristic generated by the joint functioning of specific areas of the huge network of neurons in our heads. Brain cells and areas have their own separate functions, but their functional links with one another jointly endow them with a new, “emergent” function. There are many examples of emergent characteristics. For instance, we know hydrogen and oxygen as gases. But when these molecules bind, a substance with entirely different characteristics emerges, namely water. The question of what exactly is needed from a neurobiological point of view to enable this new characteristic, consciousness, to emerge from neural activity is something that preoccupies many brain researchers. The Amsterdam neuroscientist Victor Lamme is looking for an explanation in the functioning of neurons. His theory is that for consciousness to exist, neurons in the prefrontal and parietal cortices have to relay information back to the cerebral cortex. One of the routes involved is via the thalamus. This recurrent processing extends from the purely sensory to the motor areas. Lamme believes that the selective attention crucial to our consciousness emerges because only a few of the objects that we perceive undergo recurrent processing. So we report on the stimuli on which our attention is focused while being unaware of the rest. There’s no reason to assume that basic mechanisms like recurrent processing and attention aren’t common to all animals, albeit to varying degrees. The philosopher Daniel Dennett seeks to explain consciousness as a purely bodily, chemical phenomenon, a view I share. However, he also believes that humans have a different kind of consciousness than animals because of the far-reaching impact of our linguistic development. I think it’s more logical to assume that animals have a different degree of consciousness. And although there are differences between species in this regard—a magpie’s ability to recognize itself in a mirror is far removed from a dog’s ability to distinguish the smell of its own urine from that of another dog—animals can be said to possess rudimentary self-consciousness. In humans, consciousness doesn’t depend on language, by the way. People whose language areas have been disabled after a stroke are still fully conscious of their surroundings and of themselves. By nodding or shaking their heads they can make considered decisions, even if they can no longer verbalize them.

  The importance of being conscious of your surroundings and of yourself is primarily expressed in social interaction, which involves observing and constantly interpreting your situation compared to others and learning from the mistakes that you make in this process. And that brings us back to Charles Darwin and Frans de Waal, who pointed out the enormous evolutionary importance of individuals being able to function well in the complex social interaction of the group (see chapter 20).

  8

  Aggression

  BORN AGGRESSIVE

  I have heard of cases in which a desire to steal and a tendency to lie appeared to run in families of the upper ranks.

  Charles Darwin, The Descent of Man, 1871

  Humankind is an aggressive species, just like chimpanzees. It’s not for nothing that we share ancestors. In the 1960s and 1970s there was a universal belief in social engineering. Give everyone a good environment in which to live, and aggression and crime would disappear overnight. Anyone who thought differently was publicly reviled. Now that it’s once again permissible to consider the biological background to our behavior, we can also look at the question of why one person is more aggressive than another and why some are more likely than others to commit crimes.

  Boys are more aggressive than girls. That’s something that’s determined before birth. The peak in testoste
rone that male fetuses produce halfway through pregnancy makes them more aggressive for the rest of their lives. Girls with adrenal gland abnormalities that cause them to produce too much testosterone before birth are also much more aggressive later. And hormone-like medicines taken during pregnancy can raise the aggression levels of both boys and girls.

  Some children are, however, markedly more aggressive than others, and they are more likely to commit crimes: 72 percent of young offenders in Dutch prisons have been sentenced for crimes of aggression. A strikingly high incidence of psychiatric disorders was found among this group—as high as 90 percent in the case of adolescent males. Besides antisocial behavior, there is a strong link between delinquency and addictive substance abuse, psychoses, and ADHD. Genetic factors are also influential, as has been shown from studies of twins. Tiny variations in the DNA (polymorphisms) of the gene for proteins that break down chemical messengers in the brain can lead to more aggression, alcoholism, or violent suicides. A reduction in the activity of the chemical messenger serotonin is linked to greater aggression, impulsiveness, and antisocial behavior. Some Chinese men have been found to carry a tiny variation in a gene involved in processing serotonin that is linked to extremely violent crime, antisocial personality disorders, and addiction to alcohol and other substances. Another variation of the same protein increases the likelihood of borderline personality disorder, which can also be marked by impulsiveness and aggression. So our genetic background can contribute significantly to our aggressive and criminal behavior later.