by D. F. Swaab
I’m not yet quite convinced, however, by De Waal’s claim that von Economo neurons (VEN cells or spindle cells) underpin self-consciousness, as expressed in the ability to recognize oneself in a mirror. To possess any marked degree of empathy, an animal must be able to distinguish itself from its surroundings. This ability has been studied using mirrors in the “mark test.” In the test, a paint mark is made on an animal’s forehead, after which the animal is shown its reflection in a mirror. If it realizes that it is seeing itself, it will touch the mark or try to rub it off. Dogs and cats fail this test; children over two, primates, dolphins, and—as De Waal himself showed with a particularly large mirror—elephants pass it.
Acceptance that animals, too, have emotions, is incidentally a fairly recent phenomenon in the Western world. When the first chimpanzee and orangutan were exhibited in the London Zoo in 1835, Queen Victoria pronounced them “frightful, and painfully and disagreeably human.” The young Charles Darwin, however, declared that anybody who thought that man was superior to the apes should go and take a good look. De Waal attributes our difficulty in recognizing that animals have feelings to the religions on which our culture is based. According to the Judeo-Christian doctrine, only humans have souls, and man is the only intelligent creature, having been created in God’s image. I don’t find his theory convincing. The Chinese have been equally unreceptive to the idea of animal emotions until very recently. But increasing prosperity in China is being matched by increasing interest in and empathy with animals. More and more Chinese people have pets, animal abuse meets with public outrage, and a gigantic memorial to the rhesus monkeys that were sacrificed in the name of SARS research can be found at Wuhan University.
When a journalist from a religious newspaper asked De Waal what he would change in humans if he were God, he reflected for some time, being suspicious of movements that have sought to impose social change by diktat, like social Darwinism, Marxism, and radical feminism. De Waal pointed out that both sides of human nature, that of the friendly, empathetic, and sexy bonobo and that of the aggressive, dominant chimpanzee, are necessary for a stable society. He concluded that he wouldn’t want God to change humans fundamentally but simply to increase their sense of “brotherhood” by endowing them with more empathy. I personally doubt whether this would rid the world of problems. Indeed, De Waal furnishes the other side of the argument. If you’re open to everyone and trust everyone—a trait shown by people with Williams syndrome—others will perceive your behavior as abnormal and shut you out. Moreover, empathy has its dark side. The reason humans are so good at torture is precisely because they excel at imagining what others feel. In fact, the more empathetic they are, the crueler they can be. De Waal cites the example of Nazi guards who carried out acts of unimaginable brutality in concentration camps, yet who were loving husbands and fathers in their off-duty hours. We can possess plenty of empathy and at the same time use it very selectively. The millions who revered Hitler, Stalin, and Mao were no less empathetic than we are. So De Waal might do well to ask God if he could also curb our tendency to take our lead from charismatic alpha males. Not only might this prevent future genocides and cultural revolutions, it might also reduce the likelihood of another disaster caused by corporate greed.
14
Memory
KANDEL’S RESEARCH INTO MEMORY AND THE COLLECTIVE AMNESIA OF THE AUSTRIANS
Mental activity stimulates the development of nerve cells and their axons in the part of the brain being used. In this way, existing connections between groups of cells can be reinforced by an increase in the number of terminal arborizations.
Santiago Ramón y Cajal
The only thing I recall of the international committee on which I sat twenty-five years ago is the infectious laugh of Eric Kandel. It certainly wasn’t a laugh that sprang from a happy childhood. He was born in Vienna in 1929 as Erich Kandel and was given a beautiful blue remote-controlled car for his ninth birthday. Two days later, during Kristallnacht, the Jewish Kandel family was ordered to leave their house by two Nazi policemen. When they were allowed to return home a few days later, they found that it had been ransacked. Everything was gone, including the blue car. After waiting a year for a visa, the family emigrated to the United States, where Erich changed his name to Eric. He trained as a psychiatrist, undoubtedly influenced by the fact that his first girlfriend’s parents were renowned psychoanalysts who had worked with Sigmund Freud. He was so fascinated by psychoanalysis that in 1955, while working under the famous electrophysiologist Harry Grundfest at Columbia University, he enthusiastically announced that he wanted to find the biological foundation of Freud’s theory of the psyche. Freud divided personality into three parts: the id, the unconscious, primitive component that is driven by the pleasure principle; the ego, which tries to balance the id’s desires with reality; and the superego, which acts as conscience and moral guide. Freud himself had never given any thought to where these hypothetical elements were located in the brain. Grundfest, who introduced Kandel to neuroscience, listened patiently to his unfeasible research plans and gave him the most important advice of his career: “If you want to understand the mind, you will have to study the brain cell by cell.” It was this approach, which involved studying first the cellular, then the molecular biology of memory, that ultimately won Kandel a Nobel Prize in 2000. Kandel fascinatingly describes this journey in his autobiography, In Search of Memory.
Memory is defined as the capacity to store and retrieve information. It provides us with conscious access to our past. Kandel initially focused his research on the hippocampus, a part of the brain that is crucial to memory. But the hippocampus proved too complex, and he went in search of a simpler organism to study, ultimately opting for the giant marine snail Aplysia. Kandel said that he had relied on his instincts when making the decision, just as when he took the plunge and decided to marry his girlfriend Denise. (It’s perhaps worth noting that he described Aplysia as “large, proud, attractive, and obviously highly intelligent.”) In primitive organisms like Aplysia, the various aspects of memory are present in simple reflex responses, initiated by a few extremely large neurons that make a relatively small number of synaptic connections. The simplicity of this circuitry made it comparatively easy to study aspects of the way in which neurons learn. Kandel showed that connections between neurons varied, becoming stronger or weaker in response to electrical stimuli. In other words, the nervous system didn’t consist of fixed connections like an old-fashioned telephone exchange; instead its links proved to be plastic. There are circuits, formed during development, in which innate behavioral patterns are fixed. But nervous systems also contain components that can change through learning.
Learning proved to hinge on changes in the strength of synaptic contacts. These became stronger as the neurons learned from repeated stimuli, proof of “practice making perfect.” This is the basis of memory. The various forms of learning, memory, forgetting, and thinking—and thus, in a sense, our minds themselves—are the result of synaptic contacts in different brain areas being affected by the many different chemical messengers contained in neurons. Aplysia has both short- and long-term memory, the latter of which, just like its human variant, requires repeated training interspersed with periods of rest. In the case of short-term memory (for instance briefly remembering a telephone number so that we can punch it in) only the strength of the existing synapses changes. In other words, a functional change takes place. The capacity of short-term memory is very limited: In the case of humans it is limited to fewer than twelve words or numbers, and if the information isn’t repeated it will be retained for only a few minutes. Long-term memory requires the synthesis of new proteins, because it involves forming new connections between neurons. This amounts to a structural change for which glia cells produce the essential fuel, that is, lactate. Long-term memory is sometimes compared to a computer hard disk in which information is permanently stored. Short-term memory is likened to the working memory or random-access memory (RA
M) of a computer, in which information changes every second depending on the tasks and programs being run.
Early on, memory storage can be disrupted by concussion, oxygen shortage after a heart attack, or electroshock treatment for depression. Factors like these can cause retrograde amnesia, wherein a person forgets everything that happened during the preceding period. Since memory can gradually be restored in such cases, it seems that the problem is caused by disrupted access to information rather than its storage in the brain. After a period of years, stored information is less vulnerable to disruptions of this kind. Ultimately, long-term memory contains an individual’s entire knowledge and experience of the world and themselves.
Learning causes structural changes to the brain, as Ramón y Cajal observed back in 1894 (see the epigraph to this section). In professional violinists, for instance, the part of the cerebral cortex that directs the fingers of the left hand is five times as large as in people who don’t play a stringed instrument. When I see the speed with which young children send text messages, I get the impression that the thumb areas in their cerebral cortex are considerably bigger than mine.
Kandel also unraveled the molecular processes that take place when synaptic strength alters and new synapses form, setting up a whole new research field in the process: the molecular neurobiology of cognition. He discovered the molecular mechanisms whereby information is transferred, through practice, from the short- to the long-term memory. The hippocampus (fig. 26) plays an important role in this process. At the same time, Kandel showed how a highly emotionally charged event bypasses the short-term memory and is immediately stored in the long-term memory. In those cases the amygdala (fig. 26) is crucial. Having found the likely molecular basis for normal memory deterioration as a result of aging, Kandel set up a company called Memory Pharmaceuticals. Unfortunately it hasn’t yet come up with the perfect learning pill.
Shortly before being awarded the Nobel Prize, the seventy-eight-year-old Kandel was in Amsterdam to receive the Heineken Prize for Medicine. He still had the same old infectious laugh; it rang out during the lunch. After traveling to Stockholm to collect his Nobel Prize, he returned to Vienna, where he organized a symposium on Austria’s enthusiastic response to National Socialism. It was his way of denouncing the collective denial of the role played by his homeland during the Nazi period. The man who had become famous for his work on memory was shocked to discover that schoolchildren in Austria knew nothing about Hitler or the Holocaust. While in Vienna, he was given a blue toy car exactly like the one the Nazis had stolen from him as a child. He responded laconically, saying that he was later glad that he’d had to leave the car behind in Vienna: “I went to the United States, where I had an absolutely wonderful life. And now I’ve got a Mercedes.”
THE ANATOMY OF MEMORY
If memory is localized anywhere, it’s everywhere.
Contacts between neurons change in response to neural activity. That’s how memory is encoded, and it’s a characteristic of every neuron. So you could argue that memory is located throughout the nervous system. But some brain structures are preeminently concerned with memory. Functional scans can show whether a brain area is involved in certain functions, but data on patients with local brain damage remains crucial in revealing whether or not those areas are actually necessary for a particular function. Valuable information on the role of parts of the cerebral cortex in memory has, for instance, been obtained through systematic studies of patients with brain disorders, bullet wounds, and other types of brain damage and of patients undergoing operations on the brain. Before operating on patients, the American-born Canadian neurosurgeon Wilder Penfield (1891–1976) stimulated their temporal lobes (fig. 1) with an electrical probe while they were still conscious so that he could more accurately target surgery. This sparked extremely detailed memories; some of the patients sang entire songs while lying on the operating table.
The importance of the temporal lobe for memory became clear in 1953, when the American surgeon William Scoville removed large portions of the temporal lobe from a patient famously known as H.M., a man who had developed severe epilepsy after a bicycle accident. The operation cured his epilepsy but caused profound amnesia. He was unable to learn or retain information, although his short-term memory was intact. He could, for instance, briefly remember the number seven by constantly repeating it to himself, but if he was interrupted he completely lost track of what he’d just been trying to remember. In other words, the pathway from short- to long-term memory had been cut off. If Brenda Milner, the neuropsychologist who was treating him, reentered the room only a few minutes after speaking to him, he would invariably say, “It’s been so long since I’ve seen you!” His personal history effectively ceased from the time of the operation. In his mind’s eye, he remained about thirty years of age; as he grew older, he became unable to recognize recent photos of himself. Right up to his death in 2008, he was firmly convinced that Harry Truman was president. After moving to a new house, he invariably returned to his old home, and he eventually couldn’t be trusted to go out alone.
The prefrontal cortex (fig. 15) has many functions and also coordinates the various parts of the brain that constitute the working or short-term memory. This is the memory that allows you to keep certain things briefly in mind, like the number you want to call, the plans you’re making, and the problems you need to solve. The working memory is also crucial for processing language and is thought to be underdeveloped in children who suffer from dyslexia. The prefrontal cortex works closely with the hippocampus (fig. 26) by focusing attention and selecting stimuli. In memory tests, the words that cause heightened activity in both these areas of the brain are the ones remembered best. If we just want to retain a number long enough to make a phone call, our working memory will suffice. But if we repeat that number often enough, we can store it in our long-term memory. The working memory, a short-term storage space for general use, is crucial for carrying out complex tasks and for functional performance. It enabled H.M. to remember a few words or numbers, but he was then unable to transfer that information in the normal way, through repetition, to the long-term memory. The focus of H.M.’s epilepsy was in the region of the hippocampus, two-thirds of which had been removed. (The name hippocampus, meaning “seahorse,” reflects the shape of this structure, with its ridges and curls.) He could still perfectly recall events that had taken place more than three years prior to the operation, which proved that the hippocampus wasn’t the site of remote memory storage. It was H.M.’s complete inability to form new memories after the operation that gave clues to the hippocampus’s function. Studies of neurological patients have since shown that even partial damage to the hippocampus can cause considerable, long-term impairment in the ability to create memories, or anterograde amnesia.
The hippocampus specializes in combining sensory information. The location of the restaurant you arranged to meet up at, what the person you’re meeting looks like, the sounds and smells from the kitchen, and the position of the set table are all fused into a single coherent item of autobiographical memory, the chronicle of your life. And later, at least if the dinner was worth it, this information is transferred to the long-term memory. The hippocampus does all this in close partnership with an area located nearby on the underside of the cortex: the entorhinal cortex (also called the parahippocampal gyrus, fig. 26). Scoville also removed this latter structure from H.M.’s brain. But which of the two regions does information reach first? The answer was provided by studies of epileptic patients with electrodes in their brains who performed memory tests while the electrical activity in the two regions was selectively recorded. The entorhinal cortex proved to be activated first, followed by the hippocampus.
It’s also in the entorhinal cortex that the first signs of Alzheimer’s appear, and the memory problems in the onset of the disease indeed typically concern recent information. People with Alzheimer’s may not know what happened an hour ago, but they can tell you detailed stories about a classmate at e
lementary school.
The hippocampus isn’t only crucial to memory; we also need it for spatial orientation. Brain scans of taxi drivers who spent four years learning London’s enormous and complex network of streets by heart showed a gradual increase in the volume of gray matter at the back of the hippocampus. Studies of people with damage to both sides of the hippocampus have shown that the hippocampus is necessary for imagining the future.
Fortunately, not all recent information is stored in the long-term memory. Who would want to retain every single detail of everything experienced during an entire lifetime, including every meal, every conversation, and every word in every book? That would make it incredibly difficult to locate and access really important information. There are people who are capable of remembering and reproducing enormous quantities of trivial information, like numerical series or entire phone books or train timetables. Yet this ability comes at the cost of other functions. These “savants” usually have a form of autism with severe impairments in areas such as social interaction or abstract thought (see chapter 9).
So what is normally sieved out for storage in the long-term memory? The deciding factors are the importance of the information and the emotional charge of a particular moment. Everyone knows where they were and what they were doing when they heard about the attack on the Twin Towers in New York on September 11, 2001. The amygdala (fig. 26), positioned just in front of the hippocampus in the temporal lobe, imprints memories that carry a strong emotional charge under the influence of the stress hormone cortisol. As a result, a traumatic experience is immediately stored for good in the long-term memory. And that explains why over 80 percent of our earliest memories have negative associations, as the psychologist Douwe Draaisma has shown. Remembering fear, shock, and sorrow is more important for survival than pleasant memories. However, this mechanism can cause problems. A woman with temporal lobe epilepsy, whose focus was the amygdala, kept having the same hallucinations during her seizures, in which she reexperienced a traumatic period of her youth, causing her terrible distress.