Who do you think you are?
A survey of the brain l December 23rd 2006
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Who do you think you are? Also in this section
Captain Kirk’s revenge Emotion is essential to human survival. Page 2
Brainbox A history and geography of the brain. Page 3
Dreamweavers The perfect memory is of everything and nothing. Page 5
As others see us Dealing with people changes our minds. Page 7
I think, therefore I am, I think Consciousness awaits its Einstein. Page 9 Modern neuroscience, says Geo rey Carr, is groping towards the answer to the oldest question of all: who am I?
N SEPTEMBER 13th 1848 a navvy servation moves the question who am I? Ocalled Phineas Gage was helping to from the realm of philosophy into the build a railway in Vermont. As gang fore- realm of science. man, he had the job of setting explosive Thirteen years after the incident in Cav- charges to blast a path through the hills endish, a French neurologist called Paul near a town called Cavendish. While he Broca systematised the study of how brain was tamping down one of the charges damage a ects the mind with the discov- with an iron bar, it went o prematurely, ery that certain sorts of speech defect are driving the bar clean through his head. the result of damage to part of the brain Accidents on construction projects called the left temporal lobe (see overleaf happen all the time. The reason that peo- for a refresher course on brain anatomy ple remember Gage’s is that he survived it. and function). Local brain damage of this Or, rather, his body survived it. For the sort is known to neurologists as a lesion. Gage that returned to work was not the Studying it therefore became known as the Gage who had stuck the tamping rod into lesion method. that explosive- lled hole. Before, he had Broca’s new method was taken up been a sober, industrious individual, well quickly. All sorts of strange neurological respected and destined for success. After- symptoms are now explained by speci c wards, he was a foul-mouthed drunkard, a brain damage. For example, an inability to drifter and a failure. His identity had been perceive movement (even though the changed in a speci c way by speci c dam- individual can see stationary objects) re- age to a speci c part of his brain. sults from damage to part of the temporal Gage’s accident was intriguing because lobe, and an inability to recognise faces is it cast light on the question of dualism. caused by damage to the fusiform gyrus. This is the idea that although the mind No one now questions the idea that par- the self inhabits the brain, it nevertheless ticular parts of the brain specialise in par- has an existence of its own and thus ticular activities. should not be equated with the brain. The Broca’s revolution, though, is incom- sudden change Gage underwent sug- plete. On the face of things, its discoveries A list of acknowledgments and sources can gested that brain and mind are not inde- might have meant the end of dualism, but be found at pendent. If the essence of individuality the world was not quite ready to embrace www.economist.com/surveys can be changed by a physical accident, it the mechanical explanation of self that implies that the brain is a mechanism the work of Broca and his successors im- An audio interview with the author is at which generates the self, rather than plied. For much of the 20th century, a wa- www.economist.com/audio merely an organ which houses it. This ob- tered-down version of dualism based on1 2 A survey of the brain The Economist December 23rd 2006
2 the idea of the psyche prevailed. The dis- In science, time tells. The good studies are tinction that psychiatry drew between repeated and make the textbooks. The bad neurological and psychiatric illness im- ones cannot be replicated and vanish plied that there was a psyche (whisper not down the memory hole. the word soul) that could somehow go Modern neuroscience has taken many wrong independently of physical symp- directions, and this survey will not at- toms in the brain. tempt to look at all of them. Instead, it will When that idea was challenged by the concentrate on four areas that may shed e ectiveness of physical drugs, such as light on individual identity: the study of antidepressants, in treating psychiatric ill- the emotions; the nature of memory; the ness, dualism returned in a di erent guise. ways that brains interact with each other; Many people, most of whom would not and the vexed question of what, exactly, regard themselves as dualists, think of the consciouness is. brain as being like a computer, and the Such science is very much work in pro- mind as being like a piece of software that gress. Indeed, it is science of a type that runs on that computer. But this analogy, you need to do is put someone inside an would have been familiar to Broca and his too, is awed. You do not have to do much fMRI machine, give them a task to do and contemporaries, for in many cases the re- damage to a computer to stop it being able see which bits of the brain light up. searchers have only the haziest idea of to run programs. Yet as the case of Gage Naturally, the revolution in neurosci- where they are going. In the 19th century, and numerous subsequent individuals ence brought about by this new technol- when scientists were feeling their way to- has shown, the self can plod on, albeit ogy has its critics. They point out that big wards big concepts such as the laws of changed, after quite radical brain damage. conclusions are often drawn from small thermodynamics, electromagnetics and samples, that the changes in activity ob- the periodic table without really knowing The self in action served by fMRI are indirect (the technique what they were looking for, that was nor- Broca’s heirs, though, now have a range of measures blood ow and oxygen con- mal. These days there seem to be fewer new techniques with which to investigate sumption rather than the electrical activity new big concepts around, and experi- the question. The best-known is a way of of nerve cells) and that the resolution is ments are often conducted in the expec- scanning the brain called functional mag- poor (individual points in an fMRI picture tion of particular results. But neuroscience netic-resonance imaging (fMRI). What represent two or three cubic millimetres of is one area where big concepts certainly re- makes it so powerful is that it records activ- brain tissue, which means hundreds of main to be discovered. And when they are, ity as well as anatomy. It can, if you like to thousands of nerve cells). All these criti- they are likely to upend humanity’s under- put it that way, see the self in action. All cisms are justi ed. But these are early days. standing of itself. 7 Captain Kirk’s revenge
Emotion is essential to human survival
NE neuroscientist who could not be That people like Dr Wager can now lingers to this day. Oaccused of dealing in small samples is study emotion scienti cally shows how Two people in particular came to the Tor Wager, of Columbia University in New far things have come. For much of the 20th rescue: Paul Ekman and Joseph LeDoux. York. Dr Wager studies emotions or, century, psychology sought to purge itself From the 1970s onwards, Dr Ekman, a psy- rather, he studies other people’s studies of of the sin of anthropomorphism that is, chologist at the University of California, emotion. He has gathered together every inappropriately ascribing human motives San Francisco, challenged the anthropolo- fMRI study of emotion that he can lay his and feelings to other species. The tradition gists. He was responsible for the general hands on a total of some 150 and per- known as behaviourism approached ani- agreement on the six basic emotions. He formed what statisticians call a meta-anal- mals as black boxes . Behaviourists stim- showed that the facial expressions associ- ysis. The result, illustrated overleaf, is as ulated them in di erent ways and re- ated with these emotions are universal, close as anyone has yet come to producing corded what happened. They did not ask and therefore almost certainly plumbed in an emotional map of the brain. what the animals felt. That both stymied genetically. The experience of emotion is one of the comparative studies of emotion and put In the 1980s Dr LeDoux, who is at New most fundamental parts of an individual’s out of the scienti c arena the question of York University, challenged the behaviou- identity. Most neuroscientists now recog- how emotion evolved. Meanwhile an- rists. Instead of rejecting anthropomor- nise six basic emotions: anger, disgust, thropology, in a parallel ideological t phism, he embraced it though he did so fear, joy, sadness and surprise. Dr Wager’s caused by the abuses of the eugenics carefully, noting the crucial importance of map is a neat illustration of how fMRI can movement, sought to expunge the idea the word inappropriately in the ascrip- be used to see the links between di erent that human behaviour had much in the tion of human feelings to animals. He parts of the brain that are involved in a sin- way of a genetic underpinning. This was therefore studied fear, an emotion that no gle process. the infamous nature/nurture debate that zoologist would doubt that mankind1 The Economist December 23rd 2006 A survey of the brain 3
A history and geography Brainbox of the brain
HE reason that people have brains is which is called the corpus callosum. come in pairs. The 17th-century French Tthat they are worms. This is not a (Many parts of the brain have obscure philosopher René Descartes thought it value judgment but a biological observa- Latin names.) was the seat of the human soul. tion. Some animals, such as jelly sh and This anatomical division of the brain Descartes, however, was wrong. It is in sea urchins, are radially symmetrical. re ects its evolutionary history. The fact the cerebrum’s outer layer, the cere- Others are bilaterally symmetrical, which brains of reptiles correspond more or less bral cortex, that is man’s true distinguish- means they are long, thin and have heads. to the structures known in mammals as ing feature. The cerebral cortex forms 80% Headless animals have no need for the brain stem and the cerebellum. In of the mass of a human brain, compared brains. But in those with a head the nerve mammals, the brain stem is specialised with 30% of a rat’s. It is divided into lobes, cells responsible for it and thus for sens- for keeping the heart and lungs working. four on each side. The rearmost one, ing and feeding tend to boss the others The cerebellum is for movement, posture called the occipital, handles vision. Then around. That still happens even when a and learning processes associated with come the parietal and temporal lobes, long, thin animal evolves limbs and a these two things. It is the limbic system, which deal with the other senses and skeleton. Bilateralism equals braininess. basal ganglia and cerebrum that do the in- with movement. At the front, as you A healthy human brain contains teresting stu that distinguishes mamma- would expect, is the frontal lobe. about 100 billion nerve cells. What lian brains from those of their reptilian This is humanity’s killer app , con- makes nerve cells special is that they have ancestors. taining many of the cognitive functions long lamentary projections called axons associated with human-ness (although and dendrites which carry information Soul-searching that most characteristic human function, around in the form of electrical pulses. The limbic system is itself divided. Some language, is located in the temporal and Dendrites carry signals into the cell. Ax- of the main parts are the hippocampus, parietal lobes, and only on one side, usu- ons carry signals to other cells. The junc- the amygdala, the thalamus and the hy- ally the left). Man’s huge frontal lobes are tion between an axon and a dendrite is pothalamus. The largest of the basal gan- the reason for the species’ peculiarly called a synapse. glia is the caudate. The pineal gland, shaped head. No wonder that in English- Information is carried across synapses which lies behind the limbic system, is speaking countries the brainiest of the not by electrical pulses but by chemical the only brain structure that does not species are known as highbrow . messengers called neurotransmitters. One way of classifying nerve cells is by the neurotransmitters they employ. The most complex thing in the universe Workaday nerve cells use molecules A section through the brain. The temporal lobe is not visible in this diagram called glutamic acid and gamma amino- butyric acid. More specialised cells use Corpus callosum dopamine, serotonin, acetylcholine and a Parietal lobe Frontal lobe variety of other molecules. Dopamine cells, for example, are involved in the brain’s reward systems, generating feel- Thalamus ings of pleasure. Occipital Many brain drugs, both therapeutic lobe Caudate and recreational, work either by mimick- ing neurotransmitters or altering their ac- tivity. Heroin mimics a group of molecules called endogenous opioids. Nicotine mimics acetylcholine. Prozac promotes the activity of serotonin. And cocaine boosts the e ect of dopamine, which is one reason why it is so addictive. Apart from specialised nerve cells, there is a lot of anatomical specialisation in the brain itself. Three large structures stand out: the cerebrum, the cerebellum Hypothalamus and the brain stem. In addition, there is a cluster of smaller structures in the mid- Pineal gland dle. These are loosely grouped into the Amygdala limbic system and the basal ganglia, al- though not everyone agrees what is what. Cerebellum Most brain structures, re ecting the bi- Hippocampus lateral nature of brainy organisms, are paired. In particular, the cerebrum is di- Brain stem vided into two hemispheres whose only direct connection is through three bun- dles of nerves, the most important of Source: Tor Wager 4 A survey of the brain The Economist December 23rd 2006
Once more, with feeling How the amygdala links up with other parts of the brain during the processing of emotions
Expectation and motivation circuit Visual-recognition circuit 2 Theory-of-mind shares with other species, and used some circuit of those other species to look inside the black box of the brain. Now, as Dr Wager’s ability to collect so many research papers suggests, studying emotion is all the rage. A glance at his map shows that many emotional pathways converge on two structures called the amygdalas. These are part of the limbic system, a collection of specialised struc- tures in the middle of the brain, and it was Dr LeDoux who demonstrated their im- portance in a series of experiments carried out initally on rats. He used several tech- niques to con rm that the amygdalas are the most active part of the brain when the subject is afraid. He also produced fear by stimulating the neurons of the amygdalas Valuation circuit with electricity. Subsequent work has shown that the amygdalas have the same role in people. Lose parts of them, as hap- Brain stem pens sometimes as a result of disease or Cerebellum Amygdala surgery, and you may lose your ability to experience or recognise fear. Source: Tor Wager To start with, therefore, the amygdalas were thought of as the organs of fear. This, the discovery of a gene for violence . But rassment, shame and sympathy. What perhaps, is a good example of the sort of violence is the expression of anger. Men they have in common is that they depend premature conclusion that critics worry without the gene were more easily an- not merely on what the person feeling about because things turned out to be gered. They had shorter fuses and were them thinks about others, but on what the more complicated. thus prone to spontaneous violent acts. person feeling them thinks others are First, although the amygdalas do or- The Dutch study was followed up by thinking about them. It is not the guilt or chestrate fear, they seem to do so in the one carried out in New Zealand by Terrie shame of the act itself, but the risk of being role of conductors as much as players. Cer- Mo tt, now of the Institute of Psychiatry found out that provokes the emotion. tainly this emotional orchestra cannot in London. She took the nature/nurture The evolution and function of these play without the conductor, but the ab- question head on by demonstrating that emotions is bound up with an area of re- sence of the other instruments, whose the two interact, and in predictable ways. search called theory of mind, to which this functions are shown in Dr Wager’s map, Again, the gene in question was the one for survey will return later. But, like basic will also be noticed. monoamine oxidase A. Like all genes, its emotions, the higher ones seem to have re- Second, the amygdalas also conduct activity is regulated by a DNA switch liable neurological circuits whose location other emotions. Since Dr LeDoux’s pio- called a promoter. Monoamine-oxidase-A can be identi ed by fMRI. neering work, further studies have linked promoters come in two versions. Dr Mof- Yoshiro Okubo, of Nippon Medical anger, sadness and disgust with the amyg- tt found that a combination of one ver- School in Japan, for example, has used dalas. They have also started to link other sion and abuse during childhood really fMRI to look at guilt and embarrassment. It parts of the brain with particular emo- pushed people over the edge. The pro- is not easy to evoke such feelings in some- tions. Joy, for example, involves the amyg- moter alone, or abuse alone, resulted in one lying inside an MRI machine, but Dr dala’s neighbour, the hypothalamus. some violent tendencies, but it was the Okubo thinks he has managed it. The re- Genetics is starting to contribute to the mixture that made people really angry. sults suggest that these emotions are han- study of emotion as well. The break- dled in the medial prefrontal cortex (the through came in 1993, with the discovery Illogical, captain middle of the front of the frontal lobe), the of a family (in the Netherlands, as it hap- Humans share the basic emotions identi- left posterior superior temporal sulcus pened) that included an abnormally large ed by Dr Ekman’s work with other mam- (one of the furrows towards the side of the number of violent criminals. The com- mals. That helps to make them easy to brain) and the visual cortex (towards the mon factor in the criminal members of the study. But there is also a range of what are back of the brain). family turned out to be the absence, due to referred to, for want of a better phrase, as It is surely no coincidence that much of a faulty gene, of an enzyme called mono- higher emotions. These are feelings the activity Dr Okubo found is in that amine oxidase A. This enzyme regulates a thought to be con ned, if not to humans characteristically human part of the brain, group of neurotransmitters that includes alone, then to a small subset of large- the enlarged cerebral cortex, rather than in serotonin and dopamine. Serotonin- and brained mammals, several of whom are the limbic system. And, as Dr Okubo dopamine-based neurons are both impor- related to humans. points out, some of these areas are also as- tant for emotional responses. The list of higher emotions is not as sociated with theory of mind. At the time, the nding about mono- well de ned as that of the baser ones, but The involvement of the frontal lobes is amine oxidase A was widely reported as they include things such as guilt, embar- signi cant for another reason, though: it is1 The Economist December 23rd 2006 A survey of the brain 5
2 the place where Phineas Gage took his hit. whose frontal lobe was damaged by a showed that what had gone instead were And that throws light on the question of brain tumour. When the tumour was re- his emotions. Elliot no longer felt any- what, exactly, emotions are for. moved by surgeons, the damaged tissue thing, and although he could summarise It is widely assumed that emotion and was taken out too. the choices available in a given situation as rationality are somehow opposed to each Like Gage, Elliot was a responsible well as anyone else, without his emotions other, and that rational decisions are bet- individual with a good job (and in his case to guide him he could not actually make a ter than emotional ones. In fact, emotion a family, too) before he su ered his brain choice. And, as probably happened with and reason work closely together, as has damage. The outcome was somewhat dif- Gage, that loss of emotion also changed been demonstrated by Antonio Damasio, ferent in that Elliot did not become a foul- his self. the man who revived Gage’s 19th-century mouthed wastrel; rather, he became ob- The survival value of things like fear, fame in the 20th century. sessed with detail and stopped being able disgust and joy is obvious: run away from Dr Damasio, who now works at the to make sensible decisions. The overall re- it; don’t eat it; do more of it. But the idea University of Southern California, is both sult was similar, though. He lost his job that emotions shape all activity in adap- a clinician and a researcher. He draws a and his wife and ended up an outcast. tive ways is quite a subtle one. Rationality parallel between Gage’s case and those of At rst, Dr Damasio thought that Elliot’s has its place. In the end, though, as fans of some of his own patients. In particular, he tumour had damaged his reason (both le- Star Trek will remember, it is Captain has a patient called Elliot (in neuroscience, sion studies and fMRI have shown that the Kirk, the emotion-ridden human, not Mr patients are often referred to by single frontal cortex is also the seat of the brain’s Spock, the emotionless Vulcan, who has names or initials to preserve their privacy) reasoning powers). Tests, however, the nous to run the spaceship. 7 Dreamweavers
The perfect memory is of everything and nothing
VER since the unfortunate case of H.M., Dr Maguire and her colleagues used rieties. One, known variously as explicit or Ethe subject of a lesion study second in structural MRI (which predates fMRI, pro- declarative memory, records the salient fame only to that of Phineas Gage, neuro- viding a static picture of anatomy) to study details of an individual’s life. For a taxi scientists have known that what the amyg- the hippocampuses of cabbies. They driver, the Knowledge is very salient. This dala is to emotion, the hippocampus is to found that the shape of their subjects’ hip- form of memory involves the hippocam- memory: if it is not the whole orchestra, pocampuses varied with experience. As pus. The other variety, implicit or proce- then it is certainly the conductor. the Knowledge became consolidated, the dural memory, involves the cerebellum H.M. lost the ability to form new mem- back of the hippocampus seemed to grow and the basal ganglia. You may remember ories when both of his hippocampuses while the front shrank. the anguish of individual violin lessons were destroyed by radical surgery in the With that result in their pocket, they vividly via your hippocampus, but the n- 1950s, and though he is now an old man, have turned to videogames. One of the ger movements required to play the instru- he still thinks of himself as the twenty- limitations of fMRI is that the scanners are ment will be stored in your cerebellum. something who went into the operating heavy and unportable. But Dr Maguire Even H.M. retains the ability to form new theatre. He is palpably shocked whenever wants to see what is going on in her taxi procedural memories, but his explicit he sees himself in a mirror. drivers’ brains while they are using the memory has not grown since the time of Memory is central to the question Knowledge at work. So if the machine can- his surgery. who am I? It is where the research is at its not travel around London, London has to To complicate matters further, there are most nitty-gritty, with studies of the bio- travel round the machine. She makes this two types of explicit memory. One, chemistry of synapses and the action of happen by employing a Sony videogame known as autobiographical or episodic individual genes, but also at its most eso- called The Getaway that can produce ac- memory, records the experiences them- teric, looking seriously at the function of curate representations of 110km (about 70 selves. The other, known as semantic dreams. It is, too, where cognitive neuro- miles) of central London’s roads. She uses memory, tries to generalise from these ex- science meets the videogames industry. it to project a lifelike image of driving periences. And there is evidence, to which A few years ago Eleanor Maguire, of the round London onto a mirror visible from Dr Maguire is trying to add, that the former Institute of Neurology in London, realised inside the machine. By this method, she is is stored in the hippocampus whereas the that her city has a resource available in no now studying how the hippocampus latter is consolidated in the cerebral cortex. other large centre of population: taxi driv- draws on other parts of the brain as her One of the researchers trying to tease ers who actually know where they are go- taxi drivers apply their Knowledge. out the distinction between the two is Mat- ing. To become a London cabbie, you have thew Wilson, of the Picower Institute for to learn what is called the Knowledge: the Knowledge or certainty? Learning and Memory in Cambridge, location of every street within a 10km (six- Most researchers agree that long-term Massachusetts. The Picower is one of sev- mile) radius of the centre. This takes years memory (as opposed to the short-term eral foundation-funded brain-research in- of part-time study. If you fail the exam, sort that can hold on to a telephone num- stitutes that have sprung up in America you do not get a licence. ber long enough to dial it) comes in two va- over the past few years. (Je ry Picower is a1 6 A survey of the brain The Economist December 23rd 2006
2 nancier of biotechnology rms.) connection between sleep, dreaming and stone of the theory of memory. Memory, as Dr Wilson observes, is like the establishment of long-term memories Now, with the catalogues of genes pro- everything else in biology. It has evolved has been known about for a while. Several vided by the Human Genome Project and to serve a purpose and is honed for that years ago, he began recording the pattern its animal equivalents, it is possible to purpose, which in this case is to react ap- of electrical activity in an animal’s hippo- work out which genes are involved in propriately to the stimuli an animal meets campus as it learnt something about the these changes, and try to nd out what in the environment by drawing on the ex- environment, such as how to run round a they do. So far Dr Nedivi and her team perience of previous encounters. That is particular maze, and showed that these have identi ed more than 360 genes that emphatically not the same as having a per- patterns are recapitulated during what is are unusually active in nerve cells during fect memory for each of those encounters. known as rapid-eye-movement sleep, memory formation. They do this by look- Instead, memory should generalise from which in humans is the time for dreaming. ing for messenger molecules copied from similar experiences and disregard the This recapitulation seems to be crucial to genes in the nucleus and sent out to the individual details. In other words, as time memory formation. protein-making apparatus in the cell body passes it should become more semantic He is now extending this work. He has to tell it what to make. (It is these proteins and less autobiographical. shown that rats replay their experiences in that do the actual work in cells.) If particu- And indeed that is most people’s every- their hippocampuses even when they are lar messengers accumulate at synapses in- day experience. The elderly are notorious just resting, although, intriguingly, the pat- volved in memory, or seem to be associ- for remembering every detail of their tern of electrical signals runs backwards at ated with the growth of new axons and childhood but being unable to recall what this time. dendrites, that is a good indication that the they did last week. Such inability to re- proteins encoded by those messengers member details is often regarded as a fail- Learn in your sleep and thus by the genes that generated ing, whereas so-called eidetic memory (or Even more signi cantly, if electrodes are them have some role in the process. photographic memory, its more common attached to neurons in the cortex that are The next stage is to nd out what that name) is often admired by outsiders. connected to the hippocampus, part of the role is. Using a fancy piece of genetic tech- In Dr Wilson’s view this perception is same pattern is seen there as well. How- nology that can slice any given gene out of probably wrong. Indeed, an ideal memory ever, there are di erences between what is the nucleus and eliminate it, Dr Nedivi is would react like a behaviourist’s black going on in the two places. When a rat is doing what are, in e ect, nano-lesion stud- box. It would have generalised from ex- running a particular maze, the electrical ies, starting with a gene that seems to be in- perience to such an extent that individual pattern produced in the hippocampus is volved in making dendrites grow (den- events no longer need to be remembered speci c to that maze. Such patterns, drite growth failure is a cause of several at all; merely the appropriate response to though, share general features (similar cor- forms of mental retardation). Her hope is the situation. So the fact that the elderly, ners in di erent mazes, for example, yield that each gene’s precise role can be worked who already have vast experience to draw similar signals), and it is these general fea- out by seeing what happens in its absence. on, do not waste precious storage capacity tures that show up in the cortex. Dr Wilson on adding things that will not aid their sur- interprets this as evidence of generalisa- Plato’s cave vival could well be the result of evolution- tion into semantic memory. Working at the other end of the neurologi- ary adaptation rather than an indication The recapitulation of experience in the cal scale and across a large atrium from of waning powers. form of neuronal ring patterns appears to the Picower Institute is Nancy Kanwisher Dr Wilson studies memory formation be responsible for changing the pattern of of the McGovern Institute for Brain Re- by looking at rats. More speci cally, he synapses between nerve cells in ways that search. Like the Picower, the McGovern is a looks at rats dreaming and day-dream- engrain particular memories by changing privately supported autonomous satrapy ing about what they have been up to. A the way that information ows through of the Massachusetts Institute of Technol- the neuronal network. Dr Wilson’s work ogy (Pat and Lore McGovern are entrepre- does not explain exactly how those synap- neurs who made their money, respec- tic changes happen. But Elly Nedivi, one of tively, in publishing and in computing). his colleagues at the Picower, is one of Here, Dr Kanwisher uses fMRI to look at those looking into the matter. where, exactly, in the brain various things That long-term memory is encoded, at are recognised. least in part, by changes in the strength of Dr Kanwisher’s discoveries go some the synapses between nerve cells has been way towards addressing the question of known since the pioneering work done by Platonic ideals in other words, what is the Eric Kandel of Columbia University in the essential property that makes an object, 1960s and 1970s. Admittedly, Dr Kandel say, a table rather than a pile of rewood. worked on a species of sea slug (an animal What she has found is that certain pieces he chose because its neurons are easy to of cortex are able to extract these essential see and map), and at the time many of his properties and thus react very strongly to contemporaries wondered whether the particular sorts of objects. There is, for in- ndings would hold true for more com- stance, the fusiform face area, which re- plex animals. But they did, and Dr Kan- sponds strongly (and only) to faces. The ex- del’s discovery of permanent changes in trastriate body area responds similarly to the strength and number of connections images of human bodies or body parts. between neurons has become a corner- And the parahippocampal place area re-1 The Economist December 23rd 2006 A survey of the brain 7
Platonic ideals Location of specific object-recognition areas on the hemispheres of the cerebral cortex
Left hemisphere Right hemisphere
he, too, has paid for his own institute, which is based in Seattle. Side view Initially, the Allen Institute for Brain Science had but a single mission, which it completed in September. This was to create and publish a map of where in the brain particular genes are active, so that Body parts other researchers could use it in the knowl- Faces Places edge that it was complete. Admittedly the Bottom view brain in question is a mouse brain. But the genes of mice and men correspond closely, as does much of their neuro-anat- omy, and Dr Tonegawa is not proposing to carry out his experiments on people. He does, however, plan to put the map to use Source: Mona Spiridon, Bruce Fischl, Nancy Kanwisher in a rather clever way. Many genes are actually switches that 2sponds to images of places. derstanding how such circuitry forms control the activity of other genes. By iden- This specialisation makes sense. Faces, would yield an important insight into the tifying particular switches that are active body parts and places are all important logic of the mind. It might also indicate in only one part of the brain, he can co-opt categories of natural object. Dr Kan- that the other specialised areas found by those switches into activating his gene wisher’s latest discovery, though, is par- Dr Kanwisher are the result of develop- eliminator. Thus particular genes can be ticularly intriguing. It is that there is also at mental processes rather than evolutionary eliminated from one place without a ect- least one area that handles a speci c cate- hard-wiring. ing others. That means he can shut down gory of arti cial object: written words. It, At the moment, it is hard to understand individual nervous pathways in the brain too, is always in the same place (a part of how the di erent circuits of neurons in the without a ecting the others. the cortex called the left fusiform gyrus). brain relate to one another. But Susumu This technique, which he has only just Somehow, all healthy developing brains Tonegawa, the head of the Picower, thinks begun to use, will take the lesion method not only work out that written words are a he may be able to get closer to the answer to a new level of re nement. Although category to which it is worth allocating its by using gene elimination of the sort em- anatomists can trace connections between own piece of neural anatomy, but nd it ployed by Dr Nedivi to manipulate the cir- various parts of the brain by following the easiest to accommodate that category in cuitry of the whole brain. The tool that will axons, nding our what the connections the same piece of wetware. allow him to do this is a project called the are actually for is much harder. If Dr Tone- That could not have evolved speci - Allen brain map. It is named after Paul Al- gawa’s technique works, such discoveries cally. Writing is probably too recent for len, Bill Gates’s partner in the founding of will be easier to make. The workings of the natural selection to have done its work, Microsoft. Mr Allen is even richer than Mr whole of the brain, not just the parts con- and mass literacy certainly too recent. Un- Picower and Mr and Mrs McGovern, and cerned with memory, will be laid bare. 7 As others see us
Dealing with people changes our minds
N COUNTRIES where physical torture is mind that makes human society possible. Though Dr Pinker and Dr Chomsky dis- Iillegal, the cruellest punishment that can In science, as in other elds of en- agree about the details in particular on be in icted on an individual is solitary deavour, it helps to have a good slogan. how the instinct evolved there is a lot of con nement. The I that exists by itself The language instinct , coined by Steven behavioural evidence that the basic idea is will surely go mad. Indeed, many students Pinker, of Harvard University, is an excel- right. The speed with which children learn of the eld think the evolutionary pressure lent way of describing human powers of the rules of speech is one piece of that evi- that drove the enlargement of the human communication. But although Dr Pinker dence. It is hard to see how this could hap- brain was not a need to survive in the natu- came up with the label, the idea of such an pen if what babies hear is not being ral environment but a need to negotiate instinct was originally dreamed up by plugged into some pre-programmed cir- the social one. The most obvious human Noam Chomsky, who referred to it as cuitry. Oddly, the di culty of teaching the attribute is language, and that is meaning- deep, universal grammar . Ambitious rules of writing is another piece of evi- less if there is no one to talk to. Less obvi- claims about language have been made dence. Writing is an artefact. Written lan- ous, but just as important, is the ability to for other species, from parrots to dolphins guage is no more complex than the spoken think oneself into the mind of another in to chimpanzees. None of these, however, variety, but it is a recent invention and has other words, to have a theory of mind. It is has been shown to engage in the complex- not co-evolved with the language instinct. a combination of language and theory of ity of communication that people do. Children therefore struggle to master it.1 8 A survey of the brain The Economist December 23rd 2006
zling condition known as autism. People with autism nd it hard to relate to their fellow human beings. Sometimes the con- dition is part of a wider range of problems, including low intelligence. But many peo- ple have autism pure and simple. Their intelligence is normal indeed, it is often signi cantly above average but their so- cial relations are peculiar. Simon Baron-Cohen, of Cambridge University, and Uta Frith, of University College London, think that autism results when an individual fails to develop a proper theory of mind. (Dr Baron-Cohen believes it is also an extreme manifestation of a general male tendency to be less em- pathic than females are.) All well and good, but modern neuroscience demands a mechanism. If one could be found, it might illuminate the way that theory of mind evolved in the rst place. Vilayanur Ramachandran, a researcher at the University of California, San Diego, 2 Perhaps the most persuasive behavioural ory is substantially correct. People have a thinks he may have found that mecha- evidence, though, is the way that the chil- specialised language instinct. The ques- nism: a failure of what are known as mir- dren of migrants in mixed-language com- tion is, why? ror neurons. A mirror neuron is one that is munities (for example, sugar-producing is- active both during the execution of a par- lands in which slaves spoke di erent The Machiavellian mind ticular action or the production of a feeling languages from each other and from their It is here that theory of mind the ability by the individual concerned, and also masters) are able to make up their own not only to hypothesise what other minds when that individual observes the same fully functional languages, known as cre- are thinking, but to hypothesise what they action or feeling in another individual. In oles, in a single generation. are thinking about what you are thinking other words, it mirrors the actions and Besides the behavioural evidence, the enters the explanation. The evolutionary thoughts of others. mere existence of Broca’s area, which gov- value of this is that people can anticipate The rst mirror neurons discovered (in erns speech production, and the speech- the actions of others in a way that helps the brains of monkeys) were concerned recognition area discovered a few years them. But with language, they can not only with predicting movement. However, mir- later by Carl Wernicke, points powerfully anticipate the actions of others, they can rors of emotion have now been found as to the idea that a language instinct is hard- try to manipulate them. This idea was well, and it is these that interest Dr Rama- wired in by genetics. This is an area where dubbed the Machiavellian mind by two chandran. He and his group showed, by fMRI has built convincingly on the origi- of its originators, Andrew Whiten and looking at electrical signals, that the mir- nal lesion studies. It has provided evi- Richard Byrne of St Andrews University in ror-neuron system does not work properly dence that di erent parts of speech are Scotland. in autistic children. The absence of rele- dealt with by di erent parts of Broca’s and One of the most intriguing ideas about vant mirror neurons, he suggests, means Wernicke’s areas. Not only are nouns and theory of mind comes from another sort the absence of theory of mind. For exam- verbs processed in separate locations, but of lesion study, an examination of the puz- ple, many autistic people have to learn the di erent types of noun may have their meaning of facial expressions by rote so own areas, rather in the way that Dr Kan- that they can react appropriately. wisher’s visual categories do. Such spe- Mirror, mirror That work has been followed up by cialised locations have been claimed for The right hemisphere of the cerebral cortex Marco Iacoboni, of the University of Cali- categories such as animals and tools. showing mirror-neuron activity fornia, Los Angeles, using fMRI. Dr Iaco- Nor is language processing merely a boni discovered that the mirror neurons matter of decrypting and encrypting involved in grasping the intentions of oth- sound. Deaf people who communicate us- ers are in part of the right hemisphere that ing sign languages (which have all the corresponds to Broca’s area in the left grammatical and syntactic features of spo- hemisphere, and both also correspond ken language) also do their processing in with mirror-neuron sites in monkeys. Broca’s and Wernicke’s areas. If they su er Though no one has yet proved the case, it damage to these areas, it shows up in ex- looks as though the evolution of language actly the same way that it does in those Visual cortex’s Mirror neurons’ and the evolution of theory of mind might who can hear. response to signal response to signal not only be two sides of the same coin, but from the retina from the visual cortex Taking the evidence in total, therefore, it might actually be di erent specialisations Sources: Marco Iacoboni; Public Library of Science seems likely that the Chomsky/Pinker the- of the same basic structure. 7 The Economist December 23rd 2006 A survey of the brain 9
I think, therefore I am, I think
Consciousness awaits its Einstein
N A building that looks, from the outside, ory is an idea he calls re-entrant mapping. does have a bit of pre-ordained neuro- Ilike the villain’s lair in an early James The process of learning can be viewed as anatomy (in particular, it has been tted Bond lm, a robot moves around. Called one by which reality (as perceived by the with the equivalent of a hippocampus) Darwin XI, it is the brainchild of Gerald senses) is transformed into a representa- but, like the local specialisation in a real Edelman. The building is the Neurosci- tion of reality. Mathematically, this trans- cortex observed by people like Dr Kan- ences Institute in San Diego, California, formation is described as mapping. In Dr wisher, most of the specialisation in Dar- and Dr Edelman is one of an eclectic group Edelman’s model of the brain, however, win XI simply emerges. This happens of researchers some of them neurologists there is a second process: the maps them- through the formation of specialised and some philosophers who are trying to selves are mapped by other groups of neu- groups of neurons that resemble the spe- explain what is, perhaps, the biggest mys- rons. It is this phenomenon of di erent cialised locations seen in real brains. The tery of the human brain: the nature of con- groups of neurons watching each other researchers know this because they can sciousness. His approach is to build ma- that he refers to as re-entrant mapping. track changes in the way the virtual neu- chines run by computer programs that Whether neural Darwinism is truly a rons connect to each other. work the way he thinks that brains work, theory of consciousness is moot. It may So is Darwin XI conscious? Well, it can- and then see what happens. not, for example, fully account for the feel- not speak, so no one can ask it. But the an- Consciousness is the core of an individ- ing of actually experiencing things such as swer probably depends on whether you ual’s sense of self, yet, paradoxically, it is emotions that most people would think think a rat is conscious. That illustrates a the most elusive concept in biology. Even central to conscious experience. (Philoso- big part of the problem of consciousness: framing the questions is di cult. Broadly, phers refer to such consciously experi- no one can agree on who has it, let alone though, researchers have taken three ap- enced feelings as qualia.) As a theory of what it is. In fact, the questions are linked. proaches. One is the experimental method how brains work, though, it seems to have There is a general feeling that what is spe- embraced by Dr Edelman. A second is to a lot going for it, for Dr Edelman has used it cial about humans is to do not with their look for consciousness directly in the to construct a series of ever more complex being clever, but their being conscious in a brain. The third is merely to sit and think robots that behave, in many ways, like ani- di erent way from most other animals. about the question. Though empirical sci- mals. The latest, Darwin XI, has a range of entists sometimes sco at it, this third senses: vision, hearing, touch and what Dr The inward eye method is not to be despised. After all, it Edelman refers to as taste (but which is ac- One feature of human consciousness that was by sitting and thinking about some tually sensitivity to the electrical con- students of the eld suggest might be un- paradoxical results in physics that Albert ductivity of what its taste organs are in ique is an awareness of self. The idea that Einstein was able to break out of the men- contact with). It also has whiskers. self-awareness might be speci c to hu- tal mould of classical physics and invent Darwin XI can do a lot. It can, for exam- mans and a few close relatives resulted the non-commonsensical but scienti - ple, learn to navigate mazes in search of re- from an experiment done three decades cally successful theory of relativity. wards, in the way that a laboratory rat ago by Gordon Gallup, who now works at Dr Edelman refers to his theory of con- does. It can develop preferences, thanks to the University of Albany in New York sciousness as neural Darwinism. It com- a pleasure centre that generates what Dr state. This showed that chimpanzees (and, bines two ideas. The rst, as he charmingly Edelmann calls good taste in response to as subsequently emerged, other great puts it, is that neurons which re together, those rewards. And it can forget those pref- apes) share with humans the ability to re- wire together. This process of mutual re- erences if they are no longer rewarding. cognise themselves in a mirror, whereas inforcement provides the selective pres- Other robots are able to perform simi- monkeys and various other reasonably sure that is the prerequisite for any Darwi- lar tricks, but they have to be trained spe- intelligent species, such as dogs, do not. A nian-based theory: to those neuronal ci cally to do so. The computer that runs few species that are not apes have also networks that have shall be given, from Darwin XI can work things out for itself. It passed the mirror test, including elephants those that have not, even what little they is loaded with virtual neurons, the initial and dolphins. But most animals fail it. have shall be taken away. The resulting strength of whose synapses with one an- All the species that have passed have changes are the physical basis of learning. other is allocated by a random number something in common: abnormally large The second part of Dr Edelman’s the- generator, and left to get on with things. It cerebral cortices relative to the rest of their1 10 A survey of the brain The Economist December 23rd 2006
2 brains. Whether self-awareness simply performing the role of an observing self is emerges from a large cortex or whether se- suggested by the work of Benjamin Libet at lection for it necessarily results in one is the University of California, San Fran- unclear. Perhaps it is both. What is interest- cisco. Dr Libet used electroencephalogra- ing about Dr Edelman’s theory is that phy to look at brain activity during the pro- awareness of self is built into it. That, in es- cess of making simple decisions such as sence, is what re-entrant mapping is. when to move a nger. He showed that the Such self-awareness is not, however, process which leads to the act starts about indivisible. One treatment for serious epi- three-tenths of a second before an individ- lepsy is to cut the corpus callosum and the ual is consciously aware of it. In other other nervous connections between the words, the observer is just that: an ob- two hemispheres of the brain, which stops server, not a decider. This may explain the the t passing from one hemisphere to the feeling that most people have experienced other. This does not usually a ect a per- at one time or another of having deliber- son’s everyday behaviour, but sometimes periencing. Much of the philosophical side ately done something that they had not ac- the two hemispheres have completely dif- of the study of consciousness seeks either tually wanted or intended to. ferent personalities, and where that hap- to explain qualia or to explain them away. Though Dr Libet’s experiment is almost pens the individual’s behaviour does They are, for example, at the heart of the laughably simple, it pokes a stick in a very change indeed, he ceases to be an question of dualism. For it is hard to ask deep pond. A feeling of freedom to make individual as the hemispheres ght for what is generating them and what is per- conscious choices is at the heart of most control of the body. The con ict often ceiving them without concluding that the people’s sense of themselves. Even Freud, manifests itself in the person’s hands, each processes are separate. who popularised the idea of the uncon- controlled by a di erent hemisphere, try- Daniel Dennett, a doyen among philos- scious, believed that conscious free-willed ing to do opposing things. One hand may ophers of consciousness, disparagingly re- thought could override unconscious de- try to put on a piece of clothing, for exam- fers to the putative observing self in this sires. One way of interpreting Dr Libet’s ple, while the other tries to remove it. scenario as a homunculus. He calls the work, though, could be that such free will mental stage on which the qualia suppos- is, like colour vision, simply a powerful il- Tales of mystery and imagination edly act out their play the Cartesian the- lusion. An actor in a lm, perhaps. But an At rst sight such cases seem extraordi- atre, after Descartes, the philosopher who actor reading from somebody else’s script. nary. But they are merely striking illustra- thought the soul resided in the pineal The truth, unsatisfactory though it is, is tions of a broader point: that in the brain gland. And he points out that exactly the that no one really knows. Nor does anyone nothing is ever quite what it seems, and ex- same problem applies to how the homun- know where the next breakthrough will perience and common sense are little use culus would perceive its own qualia. Turn come from. Perhaps Dr Edelman, or one of when formulating theories about the self. the theatre into a cinema, though, and Ant- his successors, will build a robot that can Two of the lesion studies mentioned in the onio Damasio quite likes the analogy. His describe its own qualia-like experiences. introduction to this survey, dealing with twist is to place the observing self in the Perhaps neuroanatomy will throw up a the inability to perceive motion and recog- lm itself, rather than in the audience. That surprising, crucial observation. Or per- nise faces, arise from the fact that visual ex- is not a particularly easy idea to grasp, but haps a bored, unregarded clerk will come perience, which for those who can see is it does seem to bear some relationship to to the rescue with an insight that domi- the dominant form of conscious experi- Dr Edelman’s idea of re-entrant mapping. nates 21st-century thinking in the way that ence, is a complete fabrication. What is That something in the brain really is relativity dominated the 20th. 7 consciously perceived is not a simple map- ping of the images that fall on the retina. In- Future surveys stead, the signals from the optic nerves are O er to readers Reprints of this survey are available at a price of Countries and regions deconstructed and re-formed in a process £2.50 plus postage and packing. Britain February 3rd 2007 so demanding that it involves about a third A minimum order of ve copies is required. America’s South March 3rd 2007 of the cerebral cortex. The future of the EU March 17th 2007 Even those with healthy brains get a Corporate o er Customisation options on corporate orders of 100 Business, nance, economics and ideas hint of this in the form of optical illusions. Executive pay January 20th 2007 These are patterns that the image-re- or more are available. Please contact us to discuss your requirements. European business February 10th 2007 construction process nds it confusing to O shore nance February 24th 2007 deal with. An even more obvious discord Send all orders to: between reality and perception is colour. The Rights and Syndication Department The world is not really coloured, it just 26 Red Lion Square looks that way because it is tremendously London WC1r 4HQ useful that it should, so the retina has cells Tel +44 (0)20 7576 8000 that are particularly sensitive to three dif- Fax +44 (0)20 7576 8492 ferent wavelengths of light, and the brain e-mail: [email protected] weaves the signals from them together to Previous surveys and a list of forthcoming create the phenomenon called colour. surveys can be found online Colours are good examples of qualia www.economist.com/surveys the things that people feel that they are ex-