An Evolutionary Account of Brain Laterality: Dr Iain McGilchrist

my name is David Keaney I'm retired psychiatrist from Oxford and it's really a great privilege for me to be chairing this session which proves to be absolutely fascinating we've got some first-rate speakers for you and the first of these is in McGilchrist who as many of you may know was previously a consultant psychiatrist and clinical director at the Bethlem and Maudsley hospital but before he became a psychiatrist he had another life in the humanities because he was three times elected a fellow of All Souls Oxford where he taught English literature and he made the transition from the humanities to medicine and the psychiatry's gain and I'm sure a number of you are familiar with Ian's Magisterial book the master in his emissary which was published in 2009 to rave reviews for the depth of its scholarship and profound insights into what it means to be human and so I'm particularly delighted to welcome in here today and he's going to talk to us about the eve I think it's the evolutionary aspects of brain laterality so we look forward to hearing from you thank you very much indeed and I do feel it's an honor and a great pleasure to be here and able to talk to your symposium today and I'm talking about something some work that I haven't written about yet and so I've broken with my normal habit of speaking off the cuff I've actually got a text and so part of it will be based on bits out of the few basic points from the thesis of my book the master in his emissary and later I'll be drawing on material to do with the corpus callosum that plays a role in my recurrent project a book entitled there are no things on the philosophical consequences of brain lateralization which is to be published by penguin if I ever come if I ever complete it sorry about that and so I want to suggest let me see how do I do that yes I want to suggest that we can make sense in evolutionary terms of a number of hitherto largely unexplained phenomena the fact that brains and not just ours are divided and asymmetrical and the nature and the function of the corpus callosum I also want to suggest that there's a pattern to a very large number of apparently disparate findings relating to lateralization and that inhibition plays a key role in this unimaginably complex system that is of course at least a book-length project which is one reason why I wrote one so today my emphasis will be purely on an evolutionary model of lateralization it's phenomenological consequences with which my work has been and continues to be principally concerned will necessarily remain I'm afraid unexplored now the most striking and on the surface puzzling thing about the brain this organ that exists only to make connections is it's divided nature yet it was passed over with hardly a mention never mind an attempt at explanation during my medical training it intrigued Greek physicians as long ago as the 3rd century BC who thought the right hemisphere was for perception and the left hemisphere for understanding after Wigan in 1844 deduced from a series of clinical cases that we must have two minds with two brains and the findings of Mark Dax and Paul Broca in relation to the left frontal speech area of course only two well-known following the first callosotomy procedures of Sperry and bogan in California back in the 60s there rose a plethora of theories about the different functions that who hemispheres might perform which broadly distinguished a verbal rational analytic left hemisphere from a Visio spatially orientated emotional and holistic right hemisphere though the evolutionary origin and basis of their separation remained obscure subsequent research has of course revealed that each hemisphere contributes to language visio spatial skills reason and emotion indeed to virtually every cerebral function suggesting that the by hemispheric structure of the brain is an anomaly at the same time the persistence in popular culture of outdated characterizations of hemisphere differences meant that the topic has somewhat fallen into repute disrepute I should say however there are not only functional but obvious measurable structural differences between the two hemispheres in humans such a symmetries exist at the gross anatomical level in the size and weight of each hemisphere as a whole and the sole cultural patterns on the surface but also in the size and shape of a number of defined brain areas the plane of temporarily being probably the best-known neuronal size the extent of dendritic branching lengths of axons and the extent of synaptic formation the ratio of white to gray matter also differs neurochemically the hemispheres differ in their sensitivity to hormones and to pharmacological agents and there are significant differences in the ratio of dopaminergic tuner adrenergic neurotransmission added to which as every clinician knows when it comes to function it's not just the site but the side of a lesion that makes all the difference so to say that there are no significant differences between the hemispheres is a bit of a non-starter to quote Tim crow I'm sorry that's just to show you with the sort of brain looks like and somewhere there we are yes to quote Jim Crow except in the light of lateralization nothing in human psychology or psychiatry makes any sense and oh no gun token who won germany's most prestigious science prize the liveness prize for his work on lateralization in birds comment hemispheric asymmetries pervade practically all major neural systems of the human brain there is hardly any perceptual cognitive or motor system that not affected by left/right differences of at least some of its components and I would add also not just perceptual cognitive or motor bit emotional and social why should that be the case and the corpus callosum the main body of fibers connecting the two hemispheres I'm going to come back to the corpus callosum later but for now let's just notice three things the first is that most creatures don't have one though any creature big enough to have a recognizable brain has a divided brain fish birds reptiles amphibians monotremes marsupials only mammals have a corpus callosum the rest get on with relatively exiguous Commerce's the second is that the relative size of the corpus callosum has reduced with mammalian II evolution and that much perhaps the majority of colossal function in humans is ultimately inhibitory and the third is just how normal split brain patients turned out to be barring some colorful instances of inter Manuel conflict in the first weeks or months after callosotomy in daily life normal services were resumed astonishingly quickly and completely it seems the hemispheres are not only separate and asymmetrical but happy to keep it that way structural and functional asymmetry of the brain is not only pervasive in humans and it has an ancient lineage indeed it goes back that's not a brain scan it goes back to the most primitive nervous system of which we have knowledge that of nemyt estelle avec tenses are still extant sea anemone which is over 700 million years old and living off the Isle of Wight it already like a lot of people in the Isle of like it already exhibits lateral asymmetry to signal paths W and T and B n T that are instrumental in the centralization of nerve cells in vertebrates run at right angles to one thereby creating an asymmetrical pattern of neuronal cell types according to Thomas Holstein whose team carried out the research it is the birthplace of centralization of the neural network that is to become the complex brain of a vertebrates a symmetries of behavior can be traced back more than 500 million years fossilized trilobite have a three-to-one distribution of right to left bite marks at their rear perhaps suggesting they were more alert potential attacks on their left side the nematode C elegans which evolved about 600 million years ago and which has a nervous system of just 302 neurons expresses chemoreceptors with left-right differences the slug lie max memorizes food odors asymmetrically in its pro cerebral brain divisions ha DB is also so left-right asymmetries in sensory processing behavior and neural representation as green token puts it if animals from nematodes to humans show a symmetries of brain and behavior we should expect that left/right differences provide some important Fitness benefits what are those benefits I suspect the answer is that laterality has served several functions over evolutionary history but there's no doubt that one critically important an enduring one concerns the need to pay divided attention to the world in Darwinian terms there is a need to be able to feed and keep a lookout for predators at one at the same time this requires the bringing to bear of diametrically opposed types of attention to the world simultaneously one narrow beam sharply focused fragmentary already committed to its object the other broad open sustained vigilant and uncommitted as to what it might find this is a difficult feat the solution adopted by all known animals is a divided brain in which the two halves remain sufficiently distant to function independently but sufficiently connected to function in concert this is also unsurprisingly the case in humans where the evidence is that the left hemisphere tends to yield narrow fragmentary attention and the right hemisphere broad sustained attention lateralization brings evolutionary advantages particularly in carrying out dual attention tasks this can readily be seen in chicks those that have been experimentally deprived of exposure to light on the 19th day of incubation do not lateral eyes normally and cannot so effectively combine feeding and predator detection mama's EPS with more strongly lateralized brains are better able to both forage and remain aware of predators lizards that use only their right hemisphere in exploring a new environment react faster and more efficiently than those using only the left hemisphere the same more successful individuals that use the right hemisphere for exploration and watching out for predators also use the left hemisphere for tracking prey even if the appropriate eye for the task is saved over they will try to use it in preference to the uncovered but inappropriate I story finding in more general terms separation leads to specialization which also brings advantages in fact as Gunther couldn't concisely says asymmetry pays pigeons with stronger visual asymmetry are more successful when foraging for grain scattered among pebbles there are shorter reaction times in cats that have a lateral eyes poor preference lateralized chimps are more efficient at fishing for termites similarly human individuals with pronounced language lateralization have higher verbal IQs better reading skills and better language receptivity indeed there's evidence suggesting that individual human brains that are for one reason or another less naturalized and the norm show global deficits the left hemisphere providing detached narrow beam highly focused attention is thus better suited to instrumental purposes well the right hemisphere providing broader more sustained uncommitted attention to the rest of the world makes it better at seeing and understanding the home the right hemisphere is deeply involved in social functioning not just in primates where it's specialized in the expression of social feelings that in lower animals and birds as well for example chicks preferentially use the left eye for differentiating family members of the species from one another and from those who are not familiar and in general for gathering social information many kinds of birds have been observed to approach their parents or direct courtship displays to come specific scene with the left eye that's the right hemisphere and to peck more successfully at prey using the right eye left hemisphere similarly in animals toads for example attend to their prey with the left hemisphere that interact with their fellow toads using the right hemisphere the right hemisphere is the main locus of early social experience in most mammals and just this week a study has shown that flying foxes and walruses not to mention whales and humans much prefer to protect and suckle their young on the left side well the human bits been known for a very very long time a symmetries are grossly increased in humans one interesting asymmetry concerns the posterior expansion of the left hemisphere which is on the right in your drawing then looking at the base of the brain this was said to be to do with the acquisition of language which being a complex function required to be located under one roof and took up residence almost at random in the left hemisphere which obligingly expanded to accommodate it in the language area none of this can be true for a number of reasons for instance we now know that language functions are distributed across both hemispheres so cramming all into one is hardly an adequate explanation and in any case the same expansion was present in the brain of pre-linguistic man as it is present in the brains of all the grey apes who nonetheless have no language besides rich it does nothing to account for a lesson in expansion which you can see at the top of the picture that of the right frontal cortex which is nonetheless the single largest asymmetry in the brain again not mentioned in medical school and the most recently evolved giving rise to so-called yakovlev Ian's talk this view that the brain looks as though it's been given a twist it would seem that the main distinction is not between what each hemisphere does since each is involved in everything we do but in how it does it by which I don't mean the mechanism involved but the manner in which whatever it may be is approached the take on it if you like not the what but the how it's not controversial among neurologists that the two hemispheres pay different kinds of attention to the world it's also not controversial among psychologists and philosophers that the nature of attention you pay determines what it is you find in the world it therefore follows that the two hemispheres must bring into being two kinds of experiential world the evidence that this is the case is both widespread and profound and forms the subject of my long book the master in his emissary what are these worlds like well clearly it lies well outside the scope of today's talk to explore the ramifications in any detail but in effect the consequences are far-reaching in brief the world as experienced by the left hemisphere consists of isolated parts or facts that have to be assembled by us parts which are in themselves relatively fixed certain known and familiar abstracted from context explicit general and lacking in life a lot is left out of this picture but its value is as a representation that is to say something that is no longer present to us and it's simpler nature makes it more useful just as a map is a more effective guide to the terrain it maps by leaving much out the world has experienced by the right hemisphere is by contrast constantly presencing to us as Heidegger would put it one in which newness and uniqueness are more evident than generalized familiarity one of possibility rather than certainty where there are not fixed parts but flowing changing interconnected wholes where all lives implicit in the context in which it in hears and is embodied in other words an animate world and also the world described by contemporary physics by the way this has consequences for the way we see everything from music to morality reason emotion the body time-space the world and the self I shall have to leave all that unexplored today now to the callosum so child Sherrington described living systems as requiring what he termed opponent processors whose very opposition makes possible finely calibrated responses to the environment simple examples would be flexor and extensor muscle groups or the sympathetic and parasympathetic nervous systems as has been often noted there is not just one but three such opponent processor systems in the brain one for each main axis the vertical axis the relationship between subcortical regions and the cortex the rostral caudal axis between the frontal cortex and the posterior cortex of the same hemisphere and the lateral exists that of the two hemispheres each one of them involves a relationship of balance that include both mutual potentiation and mutual inhibition to understand the relationship between the human brain hemispheres of the corpus callosum particularly as it's embodied there involves looking at each of these axes as they impinge in turn on one another in the development of the mammalian and ultimately the human brain the first mammals appeared in the Late Triassic and Jurassic period about 200 million years ago they were small creatures at first mouse or shrew like probably nocturnal living low to the ground possibly subterranean the first mammalian development was in the vertical axis that of the neocortex a mammalian invention this doubled the number of cortical layers from just three in reptilian allô cortex to six since broadly speaking the power of the brain increases with the number of cell layers the development of the neocortex with the first mammals is a radical shift in brain capacity what drove it one likely hypothesis is that to survive in their various ecological niches these small animals had to be smarter than the lumbering creatures alongside whom they lived and whom they eventually replaced and they needed sharper senses and proportionately bigger brains that tetrapod ancestors had a relatively low-resolution sense of smell poorer vision and hearing across the tactile sensitivity and unrefined motor coordination with little of the cortex devoted to sensory motor integration the first mammals then needed two things about war more sophisticated sensory information and better integrated topographical maps similarly they were initially two sensory modalities of supreme importance them olfactory and tactile both being especially important and nocturnal creatures living closer to the ground developing fur coats of course conserved heat in small animals especially vulnerable to heat loss that's what we know but it also provided an extraordinary sophistication in tactile spatial awareness the neocortex is dominated by a single primary somatosensory field sorry that's not really relevant at this point the neocortex is dominated by a single primary somatosensory field mapping sensation from the greatly expanded olfactory bulbs the skin hair follicles muscles and joint in reptiles the equivalent sensory mapping is carried out in the maze and kathal on beneath conscious access and at a level where there is a well-developed cross midline connection the tectal comma cell however the projections from there to the more consciously accepts accessible reptilian telencephalon lose their topographic organization ie they are no longer at that level a map the development in mammals of a high level map across the whole perceptual field is a crucially important step in the capacity for complex awareness of the world and the ability to make quick subtle and accurate responses to it above all it delivered the potential to integrate information a process that could not be achieved across the relatively sparse connecting fibers of the upper levels of the reptilian brain clearly what mammals needed was a superhighway connecting the two cortices a demand that became more pressing as auditory and visual processing as well as by manual coordination became more prominent over time this is of course where the corpus callosum comes in before we leave for the vertical axis notice that at its origins the neocortex began in the service of enhancement of already existing cortical functions later it would come to be both a facility tree partner and an inhibitory one and a permanent process exerting a downward inhibitory effect on the reptilian brain so to the lateral axis that of the corpus callosum non mammals as I say have no callosum instead having substantial anterior and posterior Thomas's which in most mammals have now become fairly exhibit relics but even these larger connoisseurs are very slim by comparison with the corpus callosum I should note here that the callosum is often misunderstood not only as a unifying force which clearly often isn't but also is the only means of communication between hemispheres which it never is the anterior commissure in humans although very much smaller about a fiftieth to a hundred of the size does transfer some information between hemispheres and to an even smaller extent the slender posterior commissure does too there it's mainly concerned with pupillary reflexes and they share the influences of hormones through the blood supply and of cerebral peptides through the CSF both of which those slower acting are as important as neuronal communication for regulating mental states what's more every single motor act initiated in one hemisphere gives thereby proprioceptive and visual feedback to the other hemisphere so even without the corpus callosum the two hemispheres are not completely isolated however the callosum remains by far the most immediate way in which the two hemispheres of the human brain interact and it's the mediate and not merely of connection but of hemisphere specialization as I will suggest it's thought that the callosum came into being in order to enable gaze pursuit across the midline for fast moving objects and to reinforce more generally perception in all modalities around the midline of the attentional field how do you communicate faster well one way of course is to take shorter routes no fibers that had to route forward and then back needed to take a more direct central route the other is to speed transmission with respect to the first the shorter route the initially slender hippocampal commissure began to route more and more into hemispheric fibers and eventually developed into the corpus callosum but there is a snag remember mammals have proportionately much bigger brains than other animals and that means both more information to be sent and yet at the same time longer distances over which descended moreover if brains were to remain proportionately interconnected as the number of neurons grew the number of neuronal connections of all kinds would have to grow geometrically not arithmetic aliy this is not only impossible because of the external constraint of head size but it's self-defeating because of increasing conduction delays you can attempt to address that by increasing fiber thickness which speeds transmission but the fibers then take up more room not just in the corpus callosum of course but throughout the brain moreover you can myelinate these thicker fibers but that makes them thicker still as the brain grows them and with it the complexity of its tasks there has to be a trade-off there comes a point where interconnection must be limited possibly the only viable solution and it is the one Nature has taken is specialization more specialized hemispheres communicate only on a need-to-know basis as you can see once begun this is a self-reinforcing process more specialized units need to communicate less and with less communication they become more specialized and this in turn has an effect on the corpus callosum it becomes neither more nor less important but it has to change its function what this means is that the callosum like the rest of the brain needs to differentiate and itself specialized conduction time short enough to support joint activity in both hemispheres the possible only in a few instances not in all services we find that only a small population of large diameter fibers continue to increase their diameter in species with larger brains these are the essential sensory motor tracts that enable coordination across the midline of the attentional field which was the earliest pressure after all for the evolution of the callosum indeed of all sensory input integration of auditory and visual modalities is the most highly conserved with high-resolution processing of central vision making possible accurate depth perception and binaural cells generating a cortical sound localization system a sort of sense around experience for the rest most areas do not require the same urgent coordination the colossal fiber types are arranged with the larger diameter Swifter communicating axons can acting visual motor and sensory and motor cortex and small or smaller diameter weakly myelinated slower communicating axons connecting the higher-order processing areas involving more sophisticated cognitive functions I think you can decode what the letters there stand for the frontal it's motor sensory middle back to the visual cortex so here's the point given specialization and differentiation one thing colossal tracks need to ensure is a sufficient degree of non-interference and that means inhibition a balance between imparting information at the sensory motor level and inhibiting premature involvement at the cognitive level needs to be struck the human corpus callosum contains an estimated 300 to 800 million fibers connecting topologically similar areas in either hemisphere yet only 2% of cortical neurons are connected by this tract what is more the main purpose of a large number of these connections is to stop the other hemisphere interfering although the majority of cells projecting to the corpus callosum used the facility tree neurotransmitter glutamate and/or excitatory many of them terminate on GABAergic intermediary neurons or inter neurons whose function is inhibitory as activation builds in one hemisphere the homologous region in the other hemisphere is inhibited initial excitedly response is followed by a more prolonged refractory inhibition and these effects can be seen on imaging intriguingly the cortex of primates has many more and a greater variety of types of Gavin neurons reflecting greater sophistications of inhibitory functioning than the cortex of any other mammalian order in fact inhibitory interneurons constitute about 25 to 30 percent of the entire neuronal population in the cortex of primates and within primates the largest and the most numerous such engineering are found in humans inhibitory interneurons are critical to normal functioning across a whole range of activities in the human cerebral cortex indeed the great neuropathologists Romani cahal believed that the extraordinary power of the human mind with primary dependent on the increase in the number and diversity of cortical inhibitory interneurons many of which he was the first to identify the power of opposites opponent processors once again the neural basis of schizophrenia and autism is likely to involve a complex of interrelated factors but a finding common to both conditions is smaller to lothal cross-sections equally colossal a genesis is often associated with the picture resembling autism a balance has to be struck between the facilitation and inhibition and the problem here would appear not to be that there's not enough mutual involvement of the hemispheres but not enough interhemispheric inhibition there's also a possibility that GABAergic inter neurons are dysfunctional in schizophrenia as you probably know with a similar impact on inhibitions in any case in the normal brain by inhibiting the overall activity in one hemisphere the corpus callosum may allow the other to take over for tasks more suited to its mode and thus maintain independence and the two hemispheres hence it is that the corpus callosum arises relatively late in evolution but cannot keep pace with the growth in brain size and becomes actually smaller in proportion to the volume of the brain as a whole as evolution progresses the proportion of closer fibers get smaller both as the brain gets bigger and as it becomes more asymmetrical which is presumably in itself a marker of specialization in fact as a general rule the higher the species on the phylogenetic scale or the more mature the individual organism the more restricted the commerce rural connections of all kinds and specifically in humans there's a marked decrease in the rate of growth of the corpus callosum when compared with the intra hemispheric white matter tracks such as the superior longitudinal fasciculus and the uncinate fasciculus the long tracks that help draw the processes within each hemisphere the corpus callosum itself comes to embody the predicament of the entire cortex and ultimately the human world how to hold things together and yet keep them apart now let us turn to the remaining axis and with it to the function of the frontal lobes of course one of the differences between great ape brains including human brains and those of most other mammals is the expansion of the frontal lobes in an intelligent animal such as the dog they account for about 18% of the brain in monkeys about 30% in the great apes about 35% and in humans about 37% of the entire brain and what is the frontal cortex for largely for stopping things happening its function is inhibition it is in fact the opponent process of par excellence it enables standing back from the immediacy of experience to take the broader view contextualized test hypothesis and plan for the future thus if the relationship of the frontal and posterior cortex is antagonistic yet it is in pursuit of the same goals negation is once again not by any means merely negative that enables something new to come into being much as we don't make a statue by putting things together but by clearing things out of the way standing back in the interests of distancing from experience makes possible the running of virtual worlds testing possible scenarios in the interest of either understanding the world right hemisphere or manipulating it left hemisphere better with the advent of language especially being able to go offline creates a relatively abstracted and virtual world alongside the immediate world of perceptual experience and clearly they have to be kept apart if each is to work efficiently what is becoming increasingly apparent to me is that the left hemisphere is no longer primarily concerned with reality more with theoretical constructs what evidence suggests that the left hemisphere is less veridical massiveness I'm going to have to cut it short there is perceptual superiority in the right hemisphere compared with the left in every aspect of every modality studied that this is evolutionary can be seen from the fact that in the pre human cerebral cortex the left hemisphere is less conceptual more perceptual visual spatial skills are less lateralized with more remaining in the left hemisphere than is the case in humans where that territory has been colonized by abstraction contrary to myth the right hemisphere is better at reality testing the left hemisphere draws more reliable conclusions is less prone to jump to conclusions more measured and judicious and is less subject to bias as a vast and increasing body of evidence shows what I like about the quote from Nicki Marron sake is that it comes from Gazzaniga x' laboratory and Gazzaniga was the man who 30 40 years ago said the right hemisphere has about the intelligence of the average chimpanzee but he's now had to swallow the fact that it is literally more intelligent in that you get more damage to the IQ by damage to the right hemisphere than the left brilliant research 2014 showing this very clearly in the series of 128 patients but it is also much more reliable and much better guide to just about everything in human experience it's largely responsible for our capacity for theory of mind whereby we come to understand human situations misrepresentations sorry misperceptions of space distortion shrinking expanding or flattening and of time it's breaking up into static frames or changing speed drastically a much commoner after right hemisphere damage in fact right hemisphere damage leads to loss of depth in space-time and emotion distortions of reality both in terms of delusions and hallucinations are approximately three times commoner and more extreme and intractable they occur after damage to the right hemisphere particular organic syndromes including delusional these are always after identifiable cerebral lesions so we can see where the lateralization is including delusional paranoia the familiar and bizarre syndrome of hemming neglect I know Cydia phoria and emotionally inappropriate disregard of a deficit anals agnosia the denial of a deficit a say Murtagh nausea failure to recognize the existence of a body part or a body half so mato para free now believing a body part has been substituted by an alien object prosopagnosia inability to recognize faces delusional misidentification such as Capgras syndrome in which someone or something familiar to you has been substituted or its obverse fregula syndrome and the mirrored self delusion failing to see or to recognize one's own face in a mirror Qatar's delusion believing you're dead delusions of infestation sorry I moved on one Alice in Wonderland syndrome in which there are distortions of body shape and size and also in space and time delusions of infestation phantom limbs that's to say not after having one amputated but actually experiencing a phantom extra limb or up to 6 or 7 in some cases extra limbs following a stroke mr. pleasure taking a an irrational hatred of a purportedly male limb and zine Emilia desire to have a healthy limb amputated all either almost exclusively or very much more commonly found after right hemisphere damage the fellow delusion morbid jealousy and declaran bear syndrome Romania are somewhat commoner after the right hemisphere damaged and in fact Martin Brunner reported with a colleague a couple of cases one had right hemisphere damage the other one had a I think an in fact in the in the left internal capsule but he's here and can correct me hey Otto Skippy confronting a copy of yourself at a distance shows no particular bias one way or the other and a part of course from the very significant semantic and syntactical deficit syndromes which principally follow left hemisphere damage and are its common manifestations only auto-type agnosia inability to name and identify correctly body parts is clearly commoner after left hemisphere damage in other words here is further evidence if needed that our understanding of the experienced world itself rather than our capacity to discourse about it depends very heavily indeed on the right hemisphere a further illustration comes from an extraordinary and elegant piece of research by Marcel kins borne and a Russian colleague var deemed Eglin temporarily suppressing one hemisphere at a time gave them a window just for about 15 minutes into each hemispheres world thus they were able to ask the two halves of one of the same individuals brain the same questions and compare the answers and what they asked was simply whether each of five syllogisms was true a syllogism I would remind you there's a logical structure whereby two propositions or premises taken together lead inevitably to a conclusion the classic example is all men are mortal Socrates is a man therefore Socrates is mortal in the experimental examples however there was a twist in each syllogism one of the premises was false so was the conclusion true or not here's an example all monkeys climb trees so far so good the porcupine is a monkey not so good does the porcupine climb trees or not as you can see the questions not quite straightforward between you and me that are annoyingly porcupines that climb trees so before someone pointed out I should say that this fact was clearly not known to the Russian investigators or their subjects and for present purposes we can put that out of our minds the experiment was carried out using the same five tests syllogisms on 10 different subjects each three times over first in the normal state and then with just one hemisphere functioning at a time yielding a hundred and fifty results overall the intact individual says the conclusion is untrue it's not true the porcupines not a monkey when the right hemisphere alone is asked it replies with some indignation of the porcupine is not a monkey it's prickly like a hedgehog is wrong yeah however when the isolated left hemisphere of the very same individual this is not just aggregated data the one that's previously given the indignant response is after if the conclusion is true it replies that yes the porcupine climbs trees since it is a monkey when asked by the examiner but is the porcupine a monkey the subject replies that she knows it's not nonetheless when asked again she repeats that since the porcupine is a monkey then it climbs trees again challenged by the examiner but you do know that the porcupine is not a monkey she insists on her answer why because that's what's written on this piece of paper the results were consistent across the ten subjects in fact one subject answered all the questions empirically by reference to real world knowledge when in the normal state as well as when using only her right hemisphere and answered them all formally according to the internal logic of the system when using only her left hemisphere before I close I want to just revisit quickly the phenomenon of yakovlev Ian talk I explained that conventional explanations in terms of language couldn't account for the left posterior expansion but language bridges the gap between abstraction and experience the abstract procedural elements of language it's true most of the lexicon and the grammar rule book the sort of things a computer can do do reside in the left hemisphere but all its embodied real-world aspects implicit meaning tone of voice pragmatics the understanding of an utterance as a whole in a real world context irony and things like that depend on the right hemisphere once again the problem is in thinking of the distinction is lying in a so-called function such as language rather than seeing it in a whole disposition towards a way of being in the world that cuts across such categories the active Le'Veon talk expands in Apes pari passu with the development of the frontal lobes that should make us think if the frontal cortex helps us stand back from the immediacy of experience this serves the overall resin depth of each hemisphere in its own way in the left more effectively to manipulate the world and in the right to understand better the world with which we stand in close relation the left posterior expansion is present in Apes because they like us have learned to abstract and conceptualize even though they don't have language and the right frontal expansion its present in Apes because they like us are deeply social animals that is what this largest and datas to expansion of the brain the right frontal cortex of course imbalance with the right posterior cortex principally sub serves empathy bonding theory of mind metaphor jokes irony the musical aspects of language flexibility tolerance and moral sensibility to sum up I have suggested that a symmetries of the nervous system are ancient and universal and have their roots in the need to pay differing kinds of attention to the world at the same time most obviously detached piecemeal attention to detail sub served by the left hemisphere in the interests of better manipulation and exploratory sustained attention to the whole field with a view to better understanding sub served by the right I mentioned in passing that this has predictable effects on the way in which the two hemispheres differently approach every aspect of experience that the difference between the hemispheres is not that they deal with different so-called functions but that they both deal with all such functions just in a predictably and reliably different way over time the hemispheres have become necessary more specialized for reasons that make it can be understood in evolutionary terms and for such reasons the left hemisphere has become a largely virtual realm the fact that our thinking as a society seems a graceless queued towards the take on the world promoted by the left hemisphere is worrying but again that is not my topic for today thank you very much thanks very much if I could could kick-off think about the evolution of man the the cognitive revolution as it some has been caused around 70,000 years ago when suddenly all the artifacts of culture started to become evident it's a bit of a puzzle as I understand it what happened to the brain at that time when all the things that we think makers characteristically human suddenly started appearing and I wonder if you had any insights into what led this onset of cultural evolution from that point I have no good reason to to espouse any particular theory it's an area for anthropologists and the anthropologist don't have an explanation that I'm aware of there are very serious to do with the the wiping out of certain hominid types by others who came in from other areas of the world but I mean we don't know and I haven't got an answer it just sounds as though that the brain has developed a new capacity the capacity for effective language for ideology that that came in at that stage and whether there we have any insights into what may be going on well one possible thing is development of abstract ways of thinking and indeed language is much more necessary when you have larger groups of people living together when you have small groups the sort of I though relationship is good enough and I suggest in the master in his emissary that language as we now know it emerge from what my phone calls musi language and because of the need in larger social groups to refer to things and people individuals that weren't present and that conceptualising may lie behind that that burst forward may have been precipitated by larger social groups and that's one possibility I'm just putting it forward thank you go for it thank you very much for a fascinating talk just to maybe paraphrase or give you the same question but in a different way that david has put to you there's been a lot of interest recently in the neuroscience of religion and the evolution of religion and and it's just so happens that if that religion seemed to have arisen or dominated the life of Homo sapiens around the same time as the flourishing the cultural flourishing that david has referred to which is somewhere around 70 to 80 thousand years ago and I was just wondering in this in your laterality scheme of the brain do you have a view on on on the evolution of religion or the the the issue of spirituality and so forth that seems to be a characteristic of our species well yes I mean first of all we only think that as it were there was this rising of religion around that time because it's a sort of circular argument the evidence of it if you know what I mean we don't really know what was going on for five hundred thousand years in the brains of Neanderthal men who had larger brains than we do and who lived peacefully in social groups for long periods without destroying the planet so we don't know quite what they how they thought or what was going on there I take the possibly unfashionable view that religion is not just a cultural construct though the ways in which it manifests are culturally constructed so I would say that it's only a kind of rather reduced picture of the world which we've espoused just for the last couple of hundred years since the Enlightenment where the only culture ever to have done so and only for a very small part of our history we take it that this must be an advanced it may or it may not be I didn't want I mean we could be here all day debating that but I don't take the view that somehow a God made you suddenly evolved in the brain if you like no I mean lateralization the rain is a whole other topic because there is evidence about that can I just come back just for I mean I wasn't just reducing religion down to a set of beliefs or whatever but I mean there is a whole array of like capacities yeah that that humans evolved around that time it seems near and against we don't we don't know exactly how or what evolved but they they the capacity for synchrony for instance yeah humans have this unique capacity to synchronize exactly with other humans yeah and this is a key aspect of religiosity true because ritual is by definition a group activity and it seems that although I think there is some evidence that Apes can synchronize to an extent and there have been certain observations I think by primatologists that chimpanzees can engage in in in in certain ritualistic behavior as a group but not to the extent you know anywhere they're quite an extent that humans do yeah so I mean I wasn't just to clarify I wasn't just reducing religion down to two to a set of beliefs but a whole array will pass at ease yes and you know although there is a very nice YouTube of a cockatoo called snowball who is dancing to a beat probably the more less humans that have this capacity for rhythmical entrainment and as far as I know it's only humans that can synchronize their vocalizations to make sounds together and you're right these are very powerful things Oliver Sacks writes about the idea that in religious ceremonies in fact and once I wish you were alive to ask him quite in more detail what exactly he means by that but there is sort of entrainment of of nervous systems together questions there's this one over there can is that itself the nature of the self can preoccupy psychiatrists a lot and itself processes yes and I kind of wanted to ask something based on James's distinction between the eye and the me yeah whether you feel that's reflected in your hypotheses about lateralization and just to connect you that was what you were saying at the end about inhibitory process is going from the frontal lobes backwards and are those sort of self creating processes well I mean take the second one first I mean I take it that any massively complex systems such as the nervous system is a sort of self evolving self-perpetuating responsive system trying to say this particular thing just led to that is probably too simple but I mean about the self yes I mean I do it's a it's a big issue a big question isn't it because we mean so many different things by the self but in the master his emissary I do make a distinction between which is something quite like what the distinction that William James was making between what the right hemisphere sub serves and what the left hemisphere sub serves but it is it's it's a big area and I think the problem is that people often don't clarifies sufficiently what it is they're talking about when they talk about the self thank you for your presentation wondering what dr. Abdi spoke about the empathy and development of empathy if you think that the mirror neuron system could have a place in that kind of development of the human brain because it has been proven that or at least the iPass thesis has been advanced that great apes monkeys can actually react to stimuli even though they you know just and just if the stimuli is proposed but not if it is presented food and so on and if something somebody else eats that food or yes I mean I think the point is we couldn't mirror neurons form an important part of this story about empathy growing is that it yes well I mean I think you will know that you know after Ritz alati there was an enormous excitement about mirror neurons because some what sort of stalks in mirror neurons that sort of tailed off a little bit lately like Bitcoin but I mean certainly there are these systems or neuronal nodes but the brain particularly the right hemisphere very much is constantly in all aspects as it were responding to inhabiting the worlds of others de sette and Chaminade in in France imaging as this say you know when you see when you feel pain it's in both hemispheres when you feel my pain that's in your right hemisphere and so forth so I mean we're thinking less in terms aren't we have small areas of activation and much more in large networks and you know it may seem to some people a bit gross to talk about hemispheres as a whole but they're massively interconnected with within one another and the superior longitudinal fasciculus and the uncinate fasciculus are of vital importance in drawing together neuronal activity within a hemisphere by an order of magnitude in ten times as much as any cross talk between the hemispheres so they are very very self-involved systems and each is capable of sustaining consciousness on its own so I think rather than in short rather I mean I'm sure you're absolutely right so of course mirror neurons are there they're exciting they play a part but it's not the whole story as I understand it the people who may have done their GP training may remember a book by Roger neighbor and it had a picture of a doctor with two heads it was entitled the inner consultation and the idea was you were constantly self-monitoring so is that a function of laterality that we're able to do this whilst acting we are also monitoring and constantly revising what we're acting what we're doing I don't think it's primarily a function of lateralization no but I mean I think it involves the involves activity in both hemispheres it's probably more to do with the frontal lobes of both hemispheres enabling us to stand back from our own experience and as it were take a view on it um so that would be my my guess thank you okay one final question for Tracy go for it do you think that there is any connection between lateralization and the extreme male brain hypothesis of baron-cohen and extreme female brain by krispies well thank you for that dangerous question [Laughter] I just don't protective gear before trying to answer and I think I mean a lot of people say to me so is the left hemisphere of the male brain and the right hemisphere of the female brain and I think I know why they say that because the right brain is is big on empathy and is a more social brain and certainly certain kinds of rather procedural thinking more exaggerated in the left hemisphere but I think and here I'm treading on dangerous ground but I think that what it is is that I mean one of the things that people must sorry little parentheses here but it's quite extraordinary how often people do range without reporting naturalization more and more they are but they often didn't and they're also not separating men and women because we know that in these studies men and women lateralized on all sorts of things completely differently oddly they lateral eyes more towards it tends to be more that the males use the right hemisphere where the women use the left hemisphere in almost all the examples that I know but in any case they need to be separated data and I think if you put it together with the fact that the it's the right hemisphere that expands in relation to testosterone and that probably the most uncontroversial male sort of skill is visual spatial skills which are highly dependent on the right parietal cortex it seems unlikely that one can just carve it up in that way what my own theory is that there is a lot of evidence that mmm there are fatter tails in the distribution of males than there are in females so that's the the normal distribution is is flattened in male cases which means that you get more duds at the bottom and more stars at the top and it's not very obvious across most as a range but when you deal with you know really extreme cases then it becomes like ten to one and I suspect that that we therefore notice rather strange men who are incredibly good at sort of some kind of logical calculation but what we we don't notice is that there are also highly gifted males for right hemisphere reasons like maths and I mean maths an analogical thinking which is all great mathematicians describe not linear analytic thinking but analogical thinking is is is very much a right hemisphere thing and you know it just is a case that you know one can argue about social causes but it does seem pretty robust that that in we'll probably always be a greater number of males in in the top end of same math I think Larry Summers had to resign from Harvard for saying that so I think I'd better stop talking there on controversial point thank you very much thank you very much [Applause]

Channel: EPSIG UK

Views: 21,901

Keywords: Psychiatry

Id: TdNe5guQapk

Length: 64min 24sec (3864 seconds)

Published: Thu Feb 01 2018