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The Master and His Emissary: The Divided Brain and the Making of the Western World by Iain McGilchrist

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Is the brain is a metaphor of the world?

Starts outlining differences in cranial hemispheres suggests this is no longer a popular topic to research as many people are wrong. Even small differences in potential between the hemispheres may lead to what are large shifts at a higher level over time. The left and right hemisphere compete with each other in a winner takes all, fashion.  If one hemisphere starts a task it will finish it rather than utilise effort to switch to the other hemisphere.  Even though though such winner-takes-all effects may still be individually small, a vast accumulation of many small effects could lead ultimately to a large bias overall.  Especially since repeated preference for one hemisphere helps to entrench still further an advantage that may start out by being relatively marginal.

It might then be that the division of the human brain is also the result of the need to bring to bear two incompatible types of attention on the world at the same time, one narrow, focussed, and directed by our needs, and the other broad, open, and directed towards whatever else is going on in the world apart from ourselves. In humans, just as in animals and birds, it turns out that each hemisphere attends to the world in a different way and the ways are consistent. The right hemisphere underwrites breadth and flexibility of attention, where the left hemisphere brings to bear focussed attention.

In general the left hemisphere is more closely interconnected within itself, and within regions of itself, than the right hemisphere.  This is all part of the close focus style, but it is also a reflection at the neural level of the essentially self-referring nature of the world of the left hemisphere: it deals with what it already knows, the world it has made for itself. By contrast, the right hemisphere has a greater degree of myelination, facilitating swift transfer of information between the cortex and centres below the cortex,  and greater connectivity in general.

New stimuli lead to release of noradrenaline in the right hemisphere. Most neurones ‘fatigue’, that is to say they cease to respond, when continuously stimulated. These noradrenergic neurones do not fatigue and maintain their condition of excitation, so that exploratory attention is held open across a greater expanse of both space and time. The range of the right hemisphere is further increased by the fact that it has a longer working memory, and so is able both to access more information and hold it together at any one time for longer.  It is capable of bearing more information in mind and doing so over longer periods, with greater specificity (which also means less susceptibility to degradation over time by memory) the left hemisphere takes a local short-term view, whereas the right hemisphere sees the bigger picture.

Hierarchy of attention, for a number of reasons, implies a grounding role and an ultimately integrating role for the right hemisphere, with whatever the left hemisphere does at the detailed level needing to be founded on, and then returned to, the picture generated by the right. This is an instance of the right left right progression which is a theme of this book. Right hemisphere understands from indirect contextual clues, not only from explicit statement, whereas the left hemisphere will identify by labels rather than context (for example the left hemisphere would identifies that it must be winter because it is ‘January’, not by looking at the trees).

The right hemisphere takes whatever is said within its entire context. It is specialised in pragmatics, the art of contextual understanding of meaning, and in using metaphor. It is the right hemisphere which processes the non-literal aspects of language. This is why the left hemisphere is not good at understanding the higher level meaning of utterances such as ‘it’s a bit hot in here today’ – while the right hemisphere understands ‘please open a window’, the left hemisphere assumes this is just helpful supply of meteorological data.

Networks of dopaminergic neurones are more widely distributed in the left hemisphere than the right. Excess dopaminergic transmission, which occurs in, for example, amphetamine abuse and in high-dose treatment with anti-Parkinsonian drugs, can mimic aspects of schizophrenia because it tends to favour the left hemisphere over the right. There is an asymmetry of hemispheric function in schizophrenia, with an abnormal but overactive left hemisphere compared with the right.

The passion for collecting and organising is seen in other conditions, including Asperger’s syndrome and autism, which show right-hemisphere deficits. Ultimately if the left hemisphere is the hemisphere of ‘what’, the right hemisphere, with its preoccupation with context, the relational aspects of experience, emotion and the nuances of expression, could be said to be the hemisphere of ‘how’.

Those more likely to have anomalous patterns of lateralisation, such as left-handers, and those with dyslexia, schizophrenia, bipolar disorder, and autism, for example (together with their relatives, who may, advantageously, carry some, but not all, of the genes for the condition), are the least likely to show what might be called ‘left-hemisphere encapsulation’. In other words, in the normal brain the serial processing that forms the basis of left-hemisphere function is carefully segregated from functions that it might impair, but the corollary of this is that the holistic approach of the right hemisphere is not available to the same extent for language and conceptual thought. In anomalous lateralisation patterns, this segregation no longer occurs, with reciprocal advantages and disadvantages.

Did music or language comes first? Suggests music and that some animals communicate in ‘musilanguage’, using intonation, not just body language, to communicate with humans. Complex attack manoeuvres of killer whales, which co-ordinated entirely by what one might call ‘music’ – a ‘language’ of pitch, intonation and temporal relation.

In a now famous experiment by Simons and Chabris, subjects were asked to watch a short video clip showing a basketball game in a relatively confined indoor setting. They were asked to count how many times one team took possession of the ball. When asked afterwards, most observers were completely oblivious of the fact that a figure in a gorilla suit walks into the middle of the mêlée, turns to face the camera, beats his chest with his fists and strolls nonchalantly out the other side of the picture.  On second viewing this is so blatant, once one knows what to expect, it is hard to believe one could really have missed it. As these researchers have dramatically demonstrated, we see, at least consciously, only what we are attending to in a focussed way with the conscious left hemisphere. Since what we select to attend to is guided by our expectations of what it is we are going to see, there is a circularity involved which means we experience more and more only what we already know. Our incapacity to see the most apparently obvious features of the world around us, if they do not fit the template we are currently working with.  This is part of what Noë and O’Regan dubbed ‘the grand illusion’. Or ability to observe what we expect to see is so entrenched that it is hard to know how we can ever come to experience anything truly new.

The world of the left hemisphere, dependent on denotative language and abstraction, yields clarity and power to manipulate things that are known, fixed, static, isolated, decontextualised, explicit, disembodied, general in nature, but ultimately lifeless. The right hemisphere, by contrast, yields a world of individual, changing, evolving, interconnected, implicit, incarnate, living beings within the context of the lived world, but in the nature of things never fully graspable, always imperfectly known and to this world it exists in a relationship of care. But one can see that the generation of the greatest feats of the human spirit require integration of both hemispheric worlds.

Split-brain patients do appear to have an impoverished level of imagination and creativity, suggesting, that integrated functioning of both hemispheres is needed for such activity. The form that that integration takes may be far from straightforward, of course. It may be that, in the absence of the intact corpus callosum, it is impossible for either hemisphere to inhibit the other adequately and stop it from interfering for critical period.

Genetics are clearly important – the process that favours the gene for imitation gets started only if the crucial behaviour is partially imitable: if it is either wholly imitable (in which case the gene is irrelevant) or wholly inimitable (in which case the gene is ineffective), it won’t get started. The behaviours in question have to exert sufficient selective pressure, that is, be sufficiently important to survival. The process will work faster if the behaviours to be imitated exert greater selective pressure.

Separation of the hemispheres brought with it both advantages and disadvantages. It made possible a standing outside of the ‘natural’ frame of reference, the common-sense everyday way in which we see the world. In doing so it enabled us to build on that ‘necessary distance’ from the world and from ourselves, achieved originally by the frontal lobes, and gave us insight into things that otherwise we could not have seen, even making it possible for us to form deeper empathic connections with one another and with the world at large.

However, separation also sowed the seeds of left-hemisphere isolationism, allowing the left hemisphere to work unchecked. The view that Romanticism is a manifestation of right-hemisphere dominance in our way of looking at the world. The right hemisphere is more inclusive, and can equally use what the left hemisphere uses as well as its own preferred approach, whereas the left hemisphere does not have this degree of flexibility or reciprocity. Whereas for the Enlightenment, and for the workings of the logical left hemisphere, opposites result in a battle which must be won by ‘the Truth’, for the Romantics, and for the right hemisphere, it is the coming together of opposites into a fruitful union that forms the basis not only of everything that we find beautiful, but of truth itself.

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