The Divided Brain

Iain McGilchrist, in his seminal book on the division of the brain The Master and His Emissary, describes in much detail the differences between the two hemispheres and how these differences have shaped cultures. The processing of information and ultimate perception of reality is very different between left and right, but ultimately complementary. McGilchrist’s premise is that the left hemisphere, with it’s linear logic, mechanistic evaluation and focused deconstruction of the world into understandable parts, should serve the right hemisphere that apprehends the “big picture”, having a sense of the whole, the organic, and tolerance for the ambiguous.
We are all familiar with the popular-science notion of the right brain representing an individual’s emotional, creative, dreamy side while the left represents the logical, numerical, grounded side. But the two are far from mutually exclusive, as both creativity and “logic” require the hemispheres to work together. There are myriad similarities between the two sides but some significant functional differences also. The key is not to focus merely on the parts but to comprehend the systemic whole. Like an orchestra with the violins positioned to the left and cellos to the right, the separation is apparent when observing the orchestra on stage but lost to us as we are caught up in the beauty and complexity of the music.
So what is the current state of knowledge on the differences between the hemispheres? The following page lays out a few differences based on McGilchrist’s work. But bear in mind that this is only a representative list of the extensive differentiation that can be drawn between left and right hemispheres.

Right Hemisphere

• More white matter—facilitating faster transfer of information across regions, reflected in an increased ability to hold global attention.
• More sensitive to testosterone.
• More reliant on noradrenaline.
• More intimately connected with the limbic system—identifies emotions faster and more accurately than the left and is more involved in emotional expression (except anger).
• Open to broad awareness; on the lookout in a broad and flexible way with vigilance and global sustained attention—sees the “whole”.
• Processes information in a non-focal manner.
• Attends to the peripheral field of vision and the entire left–right visual field.
• Alert and attentive to the new and the novel—awareness begins in the right hemisphere, grounding and integrating the experience, before being further processed in the left on a more detailed level
• More engaged in the learning of new information—explores.
• Outperforms the left when prediction is difficult; more capable of shifting the frame of reference (important for problem solving).
• Can associate words or objects that are not closely related; can understand unfamiliar (non-clichéd) metaphor.
• Better able to integrate perceptual processes from different senses.
• Longer working memory.
• Recognises broad or complex patterns.
• More involved in insight and deductive reasoning.
• Sees things in context and in terms of relationships; attentive to context in conversation—vital for a sense of humour.
• Can recognise the individual and uniqueness within a category, such as recognising individual faces in the category of faces.
• Interested in the personal, the living, rather than the impersonal and non-living.
• Plays a primary role in empathy, the theory of “mind”, identification with others, social interaction, and emotional understanding.
• Connected with the self as an embodied whole.
• Specialises in non-verbal communication, the implicit, subtle unconscious perceptions, emotional shifts, subtle clues and meanings.
• Gives an appreciation of depth in time and space

Left Hemisphere

• Less white matter—prioritising local information transfer within regions, reflected in an increased ability to localise attention and enhancing its self-referring nature.
• More reliant on dopamine.
• Superior in the expression of anger.
• Highly focused attention to detail; local, narrowly focused attention—sees “parts”.
• Attends narrowly to the right field of view, the right side of the body, the right side of objects (demonstrated in what is known as “hemi-neglect” following a right-hemisphere stroke).
• More engaged with the known, the learned, the expected; prefers what it knows—“grasps” what is in focus and has been prioritised.
• Efficient when routine is predictable.
  Finds solutions perceived to fit best with current knowledge or schemas.
• Processes information in an increasingly focal way that suppresses information not immediately relevant.
• Suppresses the right-hemisphere ability to make distant associations among words or objects (and the broader scope of attention in general).
• Takes a local, short-term view.
• Identifies things by labels rather than context; does not deduce from context like the right hemisphere—in conversation takes things more literally and has difficulty understanding implied meaning. Things are decontextualised and interpreted by an internal logic.
• Proficient at abstraction—storing and manipulating information in abstracted types, classes, categories, and representations that are impersonal, fixed, and equivalent.
• Recognises objects in a category in a generic, non-specific way, but not the uniqueness of individuals.
• Codes non-living things and has an affinity for the mechanical.
• Better at identifying simple shapes that are easily categorised.
• Interested in the utility of things—machines, tools, man-made things.
• Sees one’s own body as an assemblage of parts from which it maintains a level of detachment.
• More sophisticated in language and symbol manipulation, with greater vocabulary and more subtle and complex syntax than the right hemisphere.

Further Information

Hemisphere Differences and Their Relevance to Psychotherapy by Iain McGilchrist