Mystery of the Left Hand

a strange breed of swordsman once fought the English here it said they always won because many were left-handed one advantage this family the KERS had was up there castles were suited for defense by both right and left handers [Music] some stairs spiraled as usual to the right the right-handed curves were posted here they could hide behind the central pillar and then used their free left hand for support right-handed attackers had no such advantages so the attacker was beaten off other stairs spiraled to the left here were the left handed curse with all the advantages even with a left-handed attacker [Music] so either way occurs one Norman Geschwind an expert on the brain and advising other doctors here in Boston about difficult cases homicide be tempted not to do any operator procedure but that's something you'll have to decide I think the interesting that that the 15 years ago the oncologists always used to say we don't need biopsies because she should treat most of these people blind now they always want biopsies a professor at both Harvard and MIT Gershwin developed a controversial theory about left-handers he also examined the old story about the curse I don't believe that story because even if there was an excess of left-handers among the curds most of them still would have been right-handed and it would still would not have made sense to design the castles for left-handed defenders unless they only used left hand the defenders on the staircase which is unlikely furthermore a left spiraling staircase gave all right-handed attackers an advantage and obviously because there's been this tremendous tradition of myths about left handedness most scientific people have tended to sort of dismiss that the whole idea saying well this is these are all fantasies and tales but as I think we'll see there are some real differences on the average between left-handers and other people the child who wrote this has dyslexia geshe wins new theory about left handedness began four years ago when he went to a conference about dyslexia so what I said was that if one wanted to study the genetics of dyslexia you should look at dyslexic but you should find out all of those things which were present in the family more often than they would be in the families of non-dyslexics and furthermore I said we shouldn't just confine this to things like learning to read or other kinds of intellectual skills but that people ought to look at medical conditions everything else well I turned out to be very fruitful comment shows you the usefulness of meetings which people sometimes wonder about because as soon as I had finished talking and as soon as there was a break an English woman came up to me and said dr. Gershwin did you really mean that and I said yes I wasn't just saying it she said well let me tell you about my family and immediately she began to describe a family in which there were dyslexics but there were some striking diseases in that family and I was very surprised by what she told me because over the years I've certainly taken histories from lots and lots of patients the sort of standard family history are going to get is that someone's father had a heart attack and someone's uncle had cancer Laden and instead of these common diseases but this woman began to describe were unusual diseases in the family these were what are called autoimmune diseases jean baker's autoimmune diseases and those of her family included a form of arthritis she also suffers from allergies as well as dyslexia well I thought that was odd and a little curious but in fact person after person came up to me at that meeting when they began to tell me about their families the same things kept coming up I came back to my office and I was thinking about this and as I'm walking on the Carter I said this was pluck which had been made to dedicate the founding of the neurology department which I'm the head and then it immediately occurred to me that the founder of that department was man named Stanley Coble in fact had been one of my teachers in medical school now Cobb himself was a lifelong severe stutterer that sent me the thinking uh about this whole thing and I then began to wonder whether the relationship was really not so much between these immune diseases and stuttering or dyslexia but whether the association might be a broader one would left-handedness now that wasn't an unreasonable step because his comp itself had pointed out in his family it was more likely to be the case that the left handed people would stutter or be dyslexic and Cobb himself was conspicuously not right-handed I can remember him in medical school drawing these fantastic anatomical diagrams on the blackboard where he would use his both hands simultaneously and he was clearly not a not a right-hander at this point professor Geschwind began to ask any left hand as he met about diseases in their families you have asthma or eczema you don't have hives I'm very allergic in my eyes to dust so it is say I would say comparable to you know people it's called allergic conjunctivitis yes well known yeah and it's obviously an allergy as well so there are two of you in the family with allergies the son who's left-handed right he's hyperactive he's hyperactive now now what else do you have does anyone in your family have allergies or so it seemed Norman Geschwind that some left-handers were indeed unusual but in a way he was not discovering anything new the left has long been thought abnormal in heraldry virtually all bends and battens run down to the right [Applause] the left side was treated as being being something wrong for example the mark of the bastard the heraldry was a bar going across the coat of arms which was called the bar sinister that meant the bastard so that the whole that there's a whole mythology built around the notion that there was something wrong with left handedness so the right hand was always shown even though about 1 in 10 individuals has always been left-handed in illustrations the left hand was reserved for something more sinister but there is something strange about the left hand it's no accident that this calligrapher writes in mirror writing left-handers find it relatively easy in the original Italian this was written by a left-handed genius Leonardo da Vinci artist and scientist as far as we know he had neither dyslexia nor immune disease but we do know he was left-handed from his own drawings regular shading from top left to bottom right is the left-handed way when Leonardo drew this his left hand was being controlled by the dominant right side of his brain while in a right-hander dominant control is by the left hemisphere so left and right handers might have different brains and these differences could perhaps be related to language 400 years later Norman Geschwind discovered differences in shape between the two sides of the brain but one brain in for often one from a left-hander didn't show these subtle differences were these from left-handers who had language disorders such as dyslexia when they were children the only way to find out was to examine the brains themselves in Geschwind laboratory his colleagues painstakingly took thousands of thin sections from the brains of dyslexics the sections were stained and then examined by his collaborator dr. gala birder they first noticed that in dyslexic brains the two hemispheres were more similar than in the majority of brains something like the symmetrical brains found in a small proportion of left-handers but they also discovered clumps of brain cells in places where they shouldn't have been dyslexic had anomalies in their brains and they had developed before birth yet it's well known that dyslexic children are as intelligent as other children here at a school in Colchester they have several dyslexic boys one of them David wrote this mouse and so what sound is coming no you yes oh you it's built oh you and what does it sound like oh you yes and what does it say David has now been taught for three months by Jean Baker who first told Geschwind about unusual diseases and dyslexia we've got the sound yes shall we make up a little sentence can you think you can't how about the mouse found out about the house can you say that the sound he'll do it alright although Geschwind had connected some cases of dyslexia with left handedness other scientists had not found the connection yes is he likely to have problems when he's had out we should not make the mistake of thinking that this is a disadvantaged group I told you that Stanley Cobb who was a very distinguished professor at the Harvard Medical School was a stutterer he was clearly a man of outstanding distinction and if you look at the child of dyslexics many of those people have terrible trauma trouble learning to read are again absolutely outstanding people Thomas Edison was a star example of someone who had the awful trouble learning to read and yet was obviously a man of great brilliance Einstein came from a similar kind of background he had he was very slow in learning how to speak Woodrow Wilson didn't learn to read all until he was nine although he came from a very educated family and yet of course he eventually became the president of the United States yet all these successful people were not noted for being left-handed so there was evidence both ways Geschwind had studied six dyslexic brains and all showed anomalies but not all were known to be left-handed otherwise all he'd done up to now was to talk to a few left-handers a lot of people particularly those who are not in science simply said well you'd shown this you found that here were all these people who were left-handed and they had these stories of immune disease in the family so that was it but I knew that one couldn't settle for that because if there's anything you know in science that it's extremely treacherous just to go on your own impressions until you do something in a proper formal way you can't really be sure that you're just getting a bad sampling of people it would be no different in this case from that of somebody deciding who was gonna win the election based on the people he spoke to next door and we know that we could be terribly wrong about the opinions of our neighbors so Geschwind decided to study a large number of completely left-handed people he also picked a group who were completely right-handed and when we compare these two groups of people what we found was this there are extreme left-handers that 10% of them reported that they had some kind of immune disease but on our right handed the figure was about 4% in other words there was a 250 percent higher rate of immune disease in our extreme left-handers than our an extreme right-handers furthermore when we looked at learning disabilities things like the selection stuttering there the data were absolutely fantastic because our extreme left-handers said ten times as high rate of dislikes your stuttering as our extreme right-handers even though the published results included a total of 2,000 people they're still controversial in any case left-handers shouldn't be alarmed I'm convinced that in fact that the left-handed population is not less advantaged from the point of view of health compared to the right-handed population it's just that they've got a different distribution of diseases now in traditionally in the past because everybody started out with a notion that something was peculiar about left hand that there's nearly everything that anybody ever studied was about what was wrong with left-handers but that was obviously a mistake we haven't yet done Studies on this but my guess is going to be that it's gonna turn out that left-handers clearly have far less of certain kinds of diseases Geschwind persevered reading and thinking because although he'd proved the connections to his own satisfaction he had as yet no theory to explain why dyslexia and especially allergies should be linked to the left hand it seemed illogical and this was another cause of the continuing skepticism among other scientists somewhere in all the facts he sensed an explanation once Geschwind recalled that his own research showed changes in dyslexic brains before birth he began formulating a remarkable new idea first of all is this curious fact than most studies show that males tend to be more left-handed than females secondly if you look at those learning disorders you look at dyslexia stuttering what is in all of those conditions there's a very strong male preponderance in those conditions and most people have never met an adult woman who's felt as badly I love everybody just about has met adult males who who stutter badly so we also knew that those conditions like dyslexia stuttering autism which are male predominant they have very high rates of left-handedness those rates are left handedness or higher than there are in other males so it seems as though there was something related to being a male which had something to do with being left-handed and being dyslexic you then have to ask the question what's the difference in the uterus between the influences on the male brain and the influences on a female brain well at the moment of conception there's remarkably little difference I mean there are only two things which differ between the male conceptus is the female concept this as the male has a Y chromosome and the female has two x chromosomes and the Y chromosome which seems to be the major factor in producing a difference between males and females seems to do one major thing the Y chromosome leads to the formation of the testicles and then the testicles of the male fetus begin to produce male hormone testosterone in utero and the male fetus has to produce testosterone because that's what changes him from a basically female form to a male now we have other information from from studies in rats that testosterone has a major effect on the development in certain parts of the brain so I then came up with the following thought is that is it that what's going on is the following that testosterone produced by the male fetus while he's in utero is slowing the development of the left side of the brain if high levels of testosterone in some babies slowed the left side of the brain that might affect the brains control of the right hand after birth and any change to the right side of the brain could affect its control of the left hand after birth if you delay the left side you're going to favor the growth of certain areas on the right side and the first thing that's going to do is going to shift the control of handedness to the right hemisphere and if testosterone is responsible for that then we're going to expect more males to be left-handed because they will have more slowing at thee of the left side so maybe Leonardo developed as a sinestro by this same mechanism before birth his testicles produced unusually large amounts of male hormone testosterone testosterone then traveled in his bloodstream to his brain and these large amounts slowed the left brain so the right brain became dominant and made him left-handed secondly we could also understand why the learning disabilities occurring more in the male's because in the cases where the delay in development is extreme we're gonna get the kinds of anomalies that we found in the childhood dyslexics those delays that will occur more often in males and more often and left-handed males that was gesh wins remarkable idea a few weeks after conception both hemispheres of the brain are at the same stage but by around 20 weeks the left side has been slowed and if testosterone levels are high the right side may take over hand control at Birth the left brain catches up but the baby might be born left-handed or in the extreme cases become dyslexic or stutter now someone might say but wait a minute according to this theory should only be males we're going to be left hands that I have learning disabilities because the female fetuses don't produce significant amounts of hormones while they're in the uterus but that's really not a problem for the following reason them all women produce testosterone normal women have testosterone the reason is that the course of making the female hormones the estrogens they go through a step in which they're producing male hormones it was always male hormone floating around so every fetus is exposed to some male hormone now the male therefore is exposed both to his own male hormone plus what his mother produces the female is pretty much exposed only the one of the mother produces but some female fetuses are going to have very high sensitivity to testosterone and those sensitive females would be born left-handed some as dyslexics or stutterers by this time others were interested dr. otis on gel under the nobel prize medical committee led a conference on Gershwin's work so now we're starting with a sample of people who have learning disorders and looking to see if there's an increased frequency of left-handedness autoimmune disease migraines Gershwin still had to explain the other link between the left hand and immune disorders normally the immune system fights off bacteria and viruses but in left-hander Sally Bundy's family it had caused allergies and it caused doctors v's allergic eyes again the problem arose before birth now what's the immune system doing when the fetus is in the uterus the fetus is protected from bacteria and viruses and things like that on the whole so the immune system during fetal life can't be there in order to combat infection well there's very good evidence that what the immune system is doing is doing during fetal life is learning to recognize self and that's an odd phrase but it's very important that in adult life that your immune system doesn't attack parts of your own body and it turns out that during fetal life the cells of the immune system are being educated they're learning to recognize what is self they're learning to recognize that any substance which is present during fetal life is something which belongs to the individual and should not be attacked in later life now what my hypothesis is is that when you get the success of testosterone effect so it's certain periods in pregnancy you're slowing the development of the immune system that at that period you're not educating the cells of the immune system to recognize self and therefore you increase the possibility of attack on the person's own body in later life so in the fetus unusually high levels of testosterone not only affect the brain but the immune system to white blood cells don't learn what is self and later in life they may attack the joints causing arthritis or any other part of the body causing many other disorders they might react to food causing allergies and migraine or to pollen causing hay fever but an overactive immune system may actually fight off other conditions we can only make a guess at this moment what they would be my guess is for instance that that left handers probably are going to have less trouble with infectious diseases because of their immune systems being superior in some way my guess is they're going to have fewer of certain kinds of cancers because the immune system combats many of the major malignancies all these ideas still have to be proved but already other surprising facts support the theory one fact Geschwind had rediscovered was about twins it's been known for over 50 years that twins have been more likely to be left-handed but it's a very good example that scientific facts tend to be neglected when people can't fit them into a theoretical picture but if you say that left handedness is related to the hormonal atmosphere in pregnancy then it becomes much easier to understand why twinning should be related the hormone levels are going to be much higher because the twin is going to be exposed not only to his own hormone production but also to that of a sibling and twins turned his interest in a strange direction among the Yoruba of West Africa one person in ten is a twin it's the highest number in the world four times that in Europe though adult inform these represent twins who died in childhood the images are clothed fed and sometimes handled so much that the features have rubbed off of course many Yoruba twins would be left-handed so other things should follow stuttering is three times as common in West Africa as it is in northern Europe or or in the United States uh and I suspect that that's related to the fact that there is this very large number of twins there's a high rate of left handedness and as a result there's going to be a higher level of stuttering on the other hand the Japanese have the lowest rate of twinning in the world or all the Orientals do so by the third of the rate in in belfast and that would make one suspect that perhaps the Japanese have lower rates of of all of these things my lord mayor and my lord lady be gentlemen King George the sixth battled against stuttering all his life and was naturally left-handed in some speeches he made telltale pauses of the meaning of difficult words enable add and to carry on to its fullest extent our campaign and research he was prevented from using his left hand for writing but not in sport but why are his successes for example his grandson Prince Charles not left-handed to guess when new left handedness was not passed directly from generation to generation and his theory helped explain why suppose you consider a male fetus or male an ovum which has been fertilized by it by the sperm from the father and there you've got this future very small male there and suppose at this moment you do what Steptoe and Edwards did you take that fertilized ovum and you put it into a different mothers whoom now what's gonna happen is that that fetus which develops out of that ovum is gonna be exposed to a different hormonal atmosphere if it gets put into a different woman's uterus because the second mother may be a much lower testosterone producer or a higher testosterone producer and as a result what we're saying is that your chance of being left-handed is gonna be in part governed by your own genetics but it's also gonna be determined by our mother and that lots of those effects are going to be effects which are not genetic and one has to presume that the feed is transmitted to a different room is going to come out as a person who's gonna be on the average quite different in many ways and I think that's a very important point because most people tend to have this notion of genetics that genetics is somehow fate that you're absolutely programmed in some particular way what's in fact very clear and what comes out of thinking about all of this is that the time when the brain is most subject to environmental influences is precisely when it's inside the uterus because that's when it's most modifiable and that's when all sorts of different environmental effects can alter how the person turns out in his training leonardo learned to be scrupulously accurate he recorded the subtle left/right differences in the human form [Music] [Applause] within the body there are more obvious left/right differences some of them are related to left handedness for centuries after Leonardo that difference was recorded again this time in the age of bronze by auguste rodin its asymmetry led to a letter in the leonard journal Nature somebody wrote in and said there's something rather strange about this statue I notice that the testicles are somewhat unusual that's been well known and every Anatomy textbook points out that the way the testicles are arranged in most people is that the right testicle is the higher one and yet somebody wrote in saying I notice that the left testicle was the higher one how could Rodin have done this and then there was a series of marvelous letters the kind of everybody's familiar with and the times discussing this and some people simply say though Rodin simply made a mistake and other people simply said well he was looking at the mirror at the time he did it so he got it backwards but in fact it turns out there's another possibility a group in China some years ago did the study of a large group of people and what they found was that most people the right testicle is the higher one and is the heavier one but it turns out that when you look at left handers that although the most common arrangement to them is they have the right testicle be the higher one and the bigger one that there's a very significant minority of left handers who have an unusual pattern so either the left testicle is higher well the left testicle is bigger and of the fair number of them deviate from this standard pattern but what could this have to do with Rodin well there's a lot of evidence the Rodin probably had severe childhood dyslexia terrible trouble in school and his father who was a very sensible man finally said to him you're making a mistake coming through the conventional system and sends him to art school which obviously turned out very well so this raises the possibility that Rodin himself was a child a dyslexic in which case he may well have been a non right hander and he may well have had an unusual had enough testes that maybe that that's what he was reproducing in that statue it's not only man who is unbalanced the whole of nature is despite their variety virtually all shells like these spiral in the same direction [Music] they're all the same way round because this enables them to mate successfully so shells reflect the asymmetry of their dead inhabitants which enabled them to have offspring and to survive why are higher organisms and particularly their brains asymmetric see the first thing you might think it is better to be symmetrical say well if the left side of the brain can carry out some particular function and if the right side could also carry it out you'd think that would be an advantage to the animal because if one side was damaged he has a reserve but the advantage of that is really very small because in most cases the animal gets serious injury to one side of his brain even if he might recover well and the state of nature he probably gets eliminated very quickly on the other hand the advantage of having asymmetry means that you've really doubled the capacity of the brain intellectually because if the left side is let's say doing something special in relation to one kind of thing and the corresponding region on the right is doing something different you now have an animal who has two talents represented in those two areas instead of one and I think the big advantage of having cerebral dominance is that you don't duplicate things and you increase the intellectual diversity if you will of the animal the left hemisphere is dominant in right-handers and also usually deals with language but the right hemisphere is dominant in left-handers could this difference between left and right handers lead to very different personalities one hears it said all the time that the left hemisphere is verbal and logical while the right hemisphere is emotional and intuitive now I think that those characterizations are really distortions of what of the real truth now there's no question that most people left hemispheres verbal I mean the evidence for that is overwhelming but the statement that the left hemisphere is logical is something that has simply a lot of people have thought followed automatically from the left hemisphere being verbal now if you think about it you realize that the equation of verbal and logical is ridiculous we all know that there are people who can get up and give superb talks in absolutely perfect English full paragraphs which are completely grammatical and that everything they say is nonsensical any illogical secondly when people talk about the right hemisphere being intuitive I must say I don't even know what that means because it seems to me that the word intuitive is a word that we use to describe people who come up with the right answer about certain problems but they don't know how they've done it well if you're gonna claim that the right hemisphere is intuitive we have to say that both hemispheres are intuitive because most of the time we don't know how the brain is is is solving problems yet we do know that the right hemisphere deals with three-dimensional space and objects this building was conceived within the architects brains from the outside towers which contained lifts stairs and plumbing right through to the center of the building now it's actually being built in the city it's the new headquarters for Lloyds of London the architects are Richard Rogers and partners six years ago this was a concept then a drawing then a model once this three-dimensional object only existed in the right hemispheres of its creators now that the glass route is going on only mundane problems remain John Young one of the partners must work out how to keep it clean and bracing that goes in at the end at the moment we've got this dark we got it here at the moment I think what we should do is to get it out further because then you've got the cleaning equipment on top good telescope out the platform can then drop between the dots on them and the main building to drop down this side or or down there [Music] then I think we'll have ourselves a solution it's a matter of thinking in three dimensions [Music] [Applause] [Music] two out of three in the richard rogers partnership are left-handed and there are more left-handers than average among architects in general we know that there are certain areas on the right side of the brain which are especially important for things like spatial function so if you take certain things like figuring out whether a particular shape when it's rotated the space is the same as another shape that's the kind of thing an architect has to be very good at and that's a kind of thing that we have evidence is he's carried out by the right side of the brain so if you have an individual who while he's in the uterus as slowing at the left side of the brain has this secondary enlargement of certain areas on the right side you're gonna get those areas being bigger and you're gonna have if you will a bigger computer to carry out some of those functions in relation to spatial function those are people are more likely to be to be left-handed and that's why you're gonna find in excess of left-handers in the population of architects the ability to think in three dimensions has been around a lot longer than buildings have you've always needed people like that even before you had architects because there were obviously people in the society even in primitive societies who would have to be clever at laying out things or building things but you don't need everyone in the society to be good at that but somebody was just telling me today about these people in Polynesia the navigators who have this fantastic memory of the sky and of the locations of the stars and the currents and so on so that they can navigate these small boats all the way across the Pacific well those are enormous ly useful people in their society because they enable them to spread all over the South Pacific and to get to all sorts of places on the other hand you don't need hundreds of them you need a few of them McEnroe Navratilova Borg Connors all these outstanding tennis champions are left-handed [Applause] well it's superb tennis player is the person who makes a fantastically accurate prediction as to exactly where that ball is going to land and exactly where he has to hit it I'm the person who can make that kind of estimation is going to be a much better tennis player just as the kind of person who can estimate exactly where a baseball is going to land and run to the precise location and catch it is going to do much better and I myself think that that's the reason why there's an excess of left-handers in athletics and I think the competitive advantage of dealing with right-handed opponents is real but I think it's of exaggerated importance guest ruins wide interests kept throwing up ideas he could incorporate into his theory here in California is the most competitive industry in the world Apple computers success depends on the quality of their products behind the main buildings is they hope the key to future success their design team team designed the Apple Macintosh personal computer in the factory one is made every 15 seconds over the five here four are left handed in an average group there'd be one at most but among brilliant mathematicians their frequent Burrell Smith is the team leader originally he studied English in a liberal arts college he taught himself mathematics and physics 55 nanoseconds in or so here the frustration I had with with liberal arts is that there's no answer you can't understand anything in his totality you know once you understand the nine allegorical levels of a Chaucer book then there's the tenth hour work level that the professor knows that he'll tell you later whereas with integrated circuits it's a very precise relationship that these parts have to have with one another in order to work and there's essentially no ambiguity I think it must be obvious to everybody that from what I've said that if you're going to be very good at geometry you that would be an advantage for the left-hander because you're gonna have spatial skills but my guess is that a lot of mathematics depends on that kind of skills although we may not understand that we may understand fully in just what way but if certain kinds of logical ability depending on the right hemisphere then it wouldn't be surprising that they're gonna be in excess of left-handers in people with certain kinds of logical ability what I really like to do is dream about things and you know when we're when we're children we dream about things all the time and we have fantasies of you know scenes that we act out in our mind that don't really exist and as we've become adults we're sort of taught no that's not okay it's not okay to dream about different things or just sort of let your mind wander and free-associate ideas and I find when I'm most creative it's when I'm not really staring at the idea itself and I'm just sort of in a mindset surrounding the idea it's really a combination of mathematics and art in the sense that there are rules that you have to operate within the mathematics exists to the point where you can analyze the circuit and determine whether you have met the rules or not [Music] [Music] the professor Geschwind is correct much of modern technology benefits from left-handers and their abilities [Music] if Geschwind is correct there are good reasons why right-handers frowned on the sinestro they think differently from right-handers as well as behaving differently they're a race apart and they have evolved because they're successful [Music] [Music] [Applause] [Music] if some left hand has become geniuses this does not imply that those left handers who appear to be at a disadvantage should be regarded as less able who knows what David will become how would Norman Geschwind want us to regard his theories well I would be distressed if people simply assumed that everything I said was completely true and I would be equally distressed if people said oh well all of this doesn't make sense and therefore they disregarding it I think that the real point is that the things that I've been talking about are all subject to experimental tests and that's the Cardinal issue the truth of scientific theories is not a function of how plausible they are it's certainly not a function of whether they fit in with common sense because common sense really has no place in science oddly enough the real measure of any scientific theory is whether it leads to experimental studies and whether it leads to experimental studies that would been unexpected and I think the one thing that I can say about that the things that I've talked about here is that they're all subject to experimental tests and that whatever the results of those experimental findings are that they will cast new light on our understanding of the human mind and on some very important properties of human beings [Applause] you

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Views: 44,569

Rating: 4.9081016 out of 5

Keywords: Norman Geschwind, Left Hand, Dyslexia, autoimmune, testosterone, inutero, Lefties, Brain, hormonal influence, dominance, left, right

Id: 2wzUAbzWHY8

Length: 48min 3sec (2883 seconds)

Published: Wed Jun 13 2018