We Are Our Brains

by D. F. Swaab

  There’s a clear evolutionary advantage in imprinting danger in the mind—for instance in wartime—so that when a similar situation occurs you’re immediately on the alert. Sometimes this natural tendency becomes pathological, however, like when a soldier returns home from a war zone but can’t shake off the feeling of being endangered. If he continues to feel fearful and under threat, if the images of war constantly replay in his brain, and if he immediately dives for cover when he hears a bang, then he’s suffering from post-traumatic stress disorder (PTSD). During the First World War this was called “shell shock,” and 306 British soldiers with the condition who refused to go back to the front were executed. PTSD is a sign that the amygdala has done its work too well, preventing the prefrontal cortex from signaling to the veteran that the danger is over. The amygdala is activated to respond to danger by the chemical messenger noradrenaline. So veterans with PTSD are treated with beta blockers (which have the opposite effect) to prevent dramatic experiences from being too strongly labeled by the amygdala and the individual from being overwhelmed by stressful memories. An exaggerated response by the amygdala to negative stimuli also underlies borderline personality disorder, whose symptoms include emotional instability and impulsiveness. In this disorder, negative emotions are linked to such a strong stress reaction that patients run an increased risk of retrograde and anterograde amnesia. H.M.’s amygdala had also been removed, along with other temporal lobe structures crucial to memory.

  H.M.’s brain was sliced into wafer-thin sections at UC San Diego, a process that could be followed online. This was the first step in a process of intense microscopic research aimed at discovering exactly which brain structures were removed or damaged in the operation that he underwent fifty-five years earlier.

  FIGURE 26. The route taken by information on its way to long-term memory starts in the entorhinal cortex, located deep in the brain in the parahippocampal gyrus. It’s briefly stored in the hippocampus in a process directed by the prefrontal cortex. From there it follows two pathways: one taking it back to the cerebral cortex for long-term memory storage, and the other—much longer—carrying it along the great arch of the fornix, suspended in the septum, to the hypothalamus, where the fibers proceed to the mammillary bodies. The information then travels via the thalamus to various parts of the cortex. The amygdala, an almond-shaped structure positioned just in front of the hippocampus in the temporal cortex, imprints memories that carry a strong emotional charge.

  THE PATH TO LONG-TERM MEMORY

  Brain damage is seen in all contact sports, from boxing, kickboxing, and rugby to soccer.

  While we sleep, the hippocampus constantly activates memories and transmits them to the cerebral cortex. The jury’s still out on whether this mainly occurs during dream sleep (REM sleep) or periods of quiet sleep. The route information takes on its way to the long-term memory starts in the entorhinal cortex. It’s then briefly stored in the hippocampus in a process directed by the prefrontal cortex. From there it follows two pathways, one taking it back to the cerebral cortex for long-term memory storage and the other—much longer—carrying it along the great arch of the fornix, suspended in the septum, to the hypothalamus, where some fibers travel to the mammillary bodies (fig. 26) and some to the hypothalamus (fig. 18). Professional boxers sustain so many blows to the head that these connections are not infrequently destroyed, causing dementia, tremors, an unsteady gait, and extreme behavioral changes—a condition known as dementia pugilistica, or “punch-drunk syndrome.” Examination of the brains of ex-boxers with this syndrome often reveals a ruptured septum, a shrunken fornix, a lack of myelin (an insulating layer) around the fibers of the fornix, undersized mammillary bodies, and an oversized third ventricle due to loss of brain tissue. Other findings include Alzheimer’s-type changes, shrinkage to the cerebral cortex, and cell death, mainly in the temporal region and the hippocampus (see chapter 12). Plenty of reason, in other words, for serious memory impairment and other malfunctions. Damage of this kind isn’t confined to boxing but extends to all contact sports, from kickboxing and rugby to soccer and American football. Infarction or bleeding in the above-mentioned areas and pathways can also cause memory impairment or even dementia. In the case of Korsakoff’s syndrome (caused by a combination of alcohol abuse and vitamin B1 deficiency due to poor diet) small hemorrhages and scars are found in the mammillary bodies. People with Korsakoff’s have memory impairments similar to those of patients with damaged temporal lobes. They fill in the gaps in their memory with made-up stories. The importance of the mammillary bodies to memory has emerged not just from problems associated with boxing, tumors, or operations (see chapter 5) but also from a bizarre accident that happened to a man during a game of billiards. His opponent’s cue was accidentally forced up his nose, penetrating the underside of the brain and damaging the mammillary bodies, leaving the poor man with severe memory problems.

  The mammillary bodies pass on information to the thalamus (fig. 2). Small infarctions in this area can lead to severe memory problems and even dementia. The information travels on from the thalamus to areas of the cerebral cortex from which memories of facts and events can be consciously recalled. This is known as the declarative or explicit memory.

  SEPARATE MEMORY STORAGE

  The case of the man who recognized his car but not his wife.

  Different aspects of an event are stored in different sites in the brain. When we try to recall something that happened, the various elements have to be pieced back together again. Any missing bits are filled up by our brains, a process of which we’re entirely unconscious. So the common comparison of memory to a computer hard disk that can reproduce everything perfectly isn’t quite accurate. A better analogy would be the way in which an archeologist tries to reconstruct an entire skeleton from a few little bones—frequently getting it wrong. Our memory is notoriously unreliable, as is often shown in court cases.

  That different types of information—music, images, and faces—are stored in different parts of the cortex emerged from cases of patients with very specific problems of recall. For instance, people who suffer damage to the temporal sulcus sometimes lose the ability to recognize faces, even of the person they’re married to, despite there being nothing wrong with their eyesight. But they are able to recognize objects, like their cars, because those memories are stored in another place. Being able to identify your Ford Fiesta but not your wife must make for some interesting household scenes. This condition is known as prosopagnosia, or face blindness. Oliver Sacks described it in The Mind’s Eye and The Man Who Mistook His Wife for a Hat. Dr. P., the man in question, was so severely afflicted that, instead of his hat, he tried to put on his wife’s head. It’s hard to conceive that he was meanwhile pursuing a distinguished career as a teacher at a music school. In its extreme form, the condition makes it difficult for people even to identify themselves in a mirror. A case is also known of a soldier who ran into his mother on the street without recognizing her when he came home on leave. Luckily it’s not quite that bad in my case, but I’ve always had trouble recognizing faces, something that often leads to embarrassing situations. I occasionally introduce myself to a person who then gazes back at me in amazement and says, “Yes, I know who you are; we’ve been on the same committee for three years now.” My father was troubled by this problem too, which does seem to run in families. It’s one of the mutations that has been passed down to me. Yet defects in pattern recognition are clearly extremely selective, because I have excellent recall when it comes to microscope samples. More than once I’ve looked at a sample I haven’t seen for several years and thought (rightly as it turned out), “Oh, that’s Mr. X or Ms. Y.” Yet if I’d met the individuals in question after a similar interval I would never be able to recognize them.

  A study in which epilepsy patients with electrodes implanted in their temporal lobes were shown hundreds of pictures of different faces revealed the existence of neurons that fire only when the person sees a photo of a celebrity like B
ill Clinton. So it’s somewhere in that part of the brain that my facial recognition problem is located. In tests on monkeys, the neurons at the base of the temporal lobe that fired when they were shown a computer-generated face fired more strongly when they saw a face they knew. The strongest response came when they were shown images in which the most typical features of a familiar face had been caricatured—something that, given my own prosopagnosia, might explain my love of cartoons.

  A recognition problem of an entirely different order occurs in Capgras syndrome. While being able to recognize a friend, partner, or close relative, the sufferer feels no emotional connection to them and is therefore convinced that they are impostors. This delusion that a loved one has been replaced by something else—a robot or extraterrestrial—leads to paranoid behavior. Capgras syndrome sometimes develops after brain damage or as a symptom of Alzheimer’s.

  That the various components of vision are processed in different parts of the brain can lead to very specific visual impairment. The psychologist Ed de Haan described the case of a patient who couldn’t see movement. When cars were in motion, she couldn’t see them, but when they stopped, they suddenly became visible. Some people can see but not recognize color or can see color but not shapes or have no perception of brightness and therefore have no idea whether they are switching a light on or off.

  The safest storage place for information is our remote memory, where we keep language and music. It’s the last part to be affected by Alzheimer’s. Speech only disappears late in Stage 7 of the system devised by Dr. Barry Reisberg to chart the progress of the disease (see chapter 18). Alzheimer’s sufferers can also retain musical skills much longer than other abilities. A professional pianist started to experience memory problems at the age of fifty-eight. By the time she was sixty-three, the dementia was so advanced that she could no longer retain anything that was said or written. But she was still able, on hearing a piece of music for the first time, to remember it and play it with musical feeling. Although her cognitive skills deteriorated sharply in the year that followed, she could still play the melodies she knew, an activity that gave her a great deal of pleasure. It seems that musical memory is regulated by a subsystem of the long-term memory located on the side of the brain (parietal cortex, fig. 1) and that it remains relatively intact. In the case of visual artists with Alzheimer’s whose artistic skills remain unimpaired, the subsystem probably lies at the rear of the brain (visual cortex, fig. 1), an area that is less affected—and last affected—by the progression of the disease (see chapter 18).

  THE IMPLICIT MEMORY IN THE CEREBELLUM

  Someone who staggers around isn’t necessarily drunk.

  The cerebellum (figs. 1 and 2) is located at the back of the brain, under the large mass of the cerebral cortex. This relatively small structure (cerebellum is Latin for “little brain”) contains 80 percent of our neurons and ensures that our movements and speech are flowing and coordinated. When you shake your head violently, for instance, it allows you to keep your eyes fixed on one point. It contains the memory of how to do things. It keeps track of motor learning during our development, from crawling to standing and walking, then cycling, swimming, playing the piano, and driving a car, and it constantly steers performance of these tasks. The program for these complex actions—our implicit memory—is stored and updated in this remarkable little computer, allowing us to perform them completely automatically. Practice makes perfect, even in the cerebellum. When we learn to drive, we initially have to think about every action (“I need to change gear, that means using the clutch, where was third gear again?”). This involves using explicit or declarative memory, the memory of facts and events, a time-consuming and highly inefficient process. By practicing the same tasks over and over, they become fully automatic and are transferred to the implicit or procedural memory in the cerebellum. When you have driven so often that you do it without thinking, it in fact becomes difficult to say (drawing on your explicit memory) exactly what actions are involved. H.M.’s implicit memory was intact, because he could learn new motor skills. His ability to trace a star that he could see in a mirror improved as he practiced day after day, but he could remember nothing of these exercises. He no longer possessed that first, explicit stage in which his brain consciously trained, but his cerebellum was practicing and perfecting new tasks unconsciously.

  The cerebellum also suppresses the impact that your own actions have on other parts of the brain. That’s why you can’t tickle yourself. Your brain wants to give priority to unexpected sensory input that might require an urgent response, and your attempts at tickling yourself (like your other actions) are expected, so the sensations they produce elsewhere are suppressed. Some people lose this mechanism after damage to the cerebellum and find that they can tickle themselves as a result.

  Damage to the cerebellum doesn’t cause paralysis, but it does make you unbelievably clumsy. Normally, if you shut your eyes, it shouldn’t be at all difficult to touch the tip of your nose with your right or left index finger. If your cerebellum is damaged because of an infarct or hemorrhage, your finger will wave about from left to right and is just as likely to land in your eye. Damage of this kind also makes it hard to walk: You stagger about with your legs wide apart, trying not to fall. A colleague of mine once stumbled off an aircraft in this way, because a blood clot had shot into his cerebellum during the long flight. Alcohol and cannabis also impair the functioning of the cerebellum and have the same impact on walking ability.

  The large neurons of the cerebellum, known as Purkinje cells, form while we’re still in the womb. But the vast majority of the small neurons, called granule cells, form only after birth. So all developmental brain disorders, including autism and pedophilia, make their mark on the cerebellum. The many cerebellar deviations found in all cell types and chemical messengers in autism could explain certain impaired motor functions, like problems with movement coordination and speed and difficulty in learning how to tie shoelaces or ride a bike. But besides its crucial role in movement, it’s becoming increasingly clear that the cerebellum is also involved in higher cognitive functions. Developmental disorders of the cerebellum, local damage, infarcts, or tumors can go hand in hand with a host of psychological problems, dyslexia, ADHD, impaired verbal intelligence, and learning disorders.

  So the cerebellum is excellently designed for learning complex tasks and actions. But it also coordinates movements that take much less trouble to learn, like the involuntary muscle movements during orgasm. Gert Holstege, who teaches neuroanatomy at Groningen University, carried out brain scans of individuals experiencing orgasm, finding an incredible amount of activity in the cerebellum in both men and women. It makes you wonder what the world would be like if training the muscle movements involved in orgasm took as much time, patience, and effort as learning to play the piano. Problems like overpopulation, global warming, and environmental pollution would never arise!

  15

  Neurotheology: The Brain and Religion

  How so many absurd rules of conduct, as well as so many absurd religious beliefs, have originated, we do not know … but it is worthy of remark that a belief constantly inculcated during the early years of life, whilst the brain is impressible, appears to acquire almost the nature of an instinct; and the very essence of an instinct is that it is followed independently of reason.

  Charles Darwin, The Descent of Man

  WHY ARE SO MANY PEOPLE RELIGIOUS?

  Whatever we cannot understand easily we call God; this saves wear and tear on the brain tissues.

  Edward Abbey

  Since it is obviously inconceivable that all religions can be right, the most reasonable conclusion is that they are all wrong.

  Christopher Hitchens

  As far as I’m concerned, the most interesting question about religion isn’t whether God exists but why so many people are religious. There are around ten thousand different religions, each of which is convinced that there’s only one Truth and that they alone possess
it. Hating people with a different faith seems to be part of belief. Around the year 1500, the church reformer Martin Luther described Jews as a “brood of vipers.” Over the centuries the Christian hatred of the Jews led to pogroms and ultimately made the Holocaust possible. In 1947, over a million people were slaughtered when British India was partitioned into India for the Hindus and Pakistan for the Muslims. Nor has interfaith hatred diminished since then. Since the year 2000, 43 percent of civil wars have been of a religious nature.

  Almost 64 percent of the world’s population is Catholic, Protestant, Muslim, or Hindu. And faith is extremely tenacious. For many years, Communism was the only permitted belief in China and religion was banned, being regarded, in the tradition of Karl Marx, as the opium of the masses. But in 2007, one-third of Chinese people over the age of sixteen said that they were religious. Since that figure comes from a state-controlled newspaper, the China Daily, the true number of believers is likely at least that high. Around 95 percent of Americans say that they believe in God, 90 percent pray, 82 percent believe that God can perform miracles, and over 70 percent believe in life after death. It’s striking that only 50 percent believe in hell, which shows a certain lack of consistency. In the Netherlands, a much more secular country, the percentages are lower. A study carried out in April 2007 showed that in the space of forty years, secularization had increased from 33 to 61 percent. Over half of the Dutch people doubt the existence of a higher power and are either agnostic or believe in an unspecified “something.” Only 14 percent are atheists, the same percentage as Protestants. There are slightly more Catholics (16 percent).