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The Master and His Emissary. The Divided Brain and the Making of the Western World

Chapter 2: What do the two hemispheres 'do'?

The focus of Chapter 2 is on what the two hemispheres do differently. There are similarities, but it is the differences that interest McGilchrist. Nevertheless he cautions against a solely analytic approach saying that both analysis (left hemisphere) and synthesis (right hemisphere) are important. In other words, we should not lose sight of the brain as a whole; a single, integrated, highly dynamic system.

Structurally the hemispheres differ in size, shape, number of neurones, neuronal size, dendritic branching and the ratio of grey to white matter. Neurochemically the hemispheres differ in sensitivity to hormones, dependence on pharmacological agents and neurotransmitters. A number of methods have been employed to study the differences between the hemispheres; brain lesions, temporary experimental hemisphere inactivation, transcranial magnetic stimulation techniques, delivering a perceptual stimulus to one hemisphere only, studying split brain subjects and EEG recordings, and employing functional neuroimaging techniques.

All these studies have their limitations. This is not a precise science. McGilchrist believes that it’s not so much what the hemispheres do differently that is of significance, but more how they do what they do differently.

McGilchrist then goes on to examine consistent differences between the two hemispheres, drawing on studies of the brain and scientific evidence to illustrate his points. Here, he has necessarily had to divide the chapter up into parts with many sub-heading, despite his reservations about doing this. In the following pages, I will list these headings and add a few notes to each.

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Links

Link to: Chapter 2 Commentary

Link to: Image Credits

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