Neuroscience - how the relationship between the left and right hemispheres of our brains shape our very nature

Epistemonikon (What is worth knowing)

The Mystery see

Lets not even presume

The mind can know the least of things

Why limit the infinite

Kill what is not ours to kill

Why make small what is measureless

Hold what cannot be caught

No where to hide anyways

Soul has no prison

Lets stop the petty game

And live the truth

See what is really there

Beyond past's lies

As the poem argues the soul is mysterious and so is the truth. What we really see is mystery and lies conceal this. Our right brain is a truth finder and knows this to be reality. However, our left brain objects as it tries to simplify the world. British psychiatrist and neuroscientist, Iain McGilchrist, author of 'The Master and his Emissary' and 'The Matter of Things' specialises in the hemispheric functioning of the brain and explains the above. This blog is centred on his latter book, where he writes - there is an 'old dichotomy, that the left hemisphere rational whilst the right hemisphere emotional'. However, 'this is profoundly mistaken, on both counts; not to mention the fact that reason and emotion are never entirely separable. Knowing the limits to reason is essential to understanding. If not coupled with contextual, implicit and intuitive understanding (in none of which the left hemisphere excels), it can magnify error.'

The brain is far from symmetrical, especially in men. Different emotions are lateralised to different sides of it; in general - anger, disgust, elation (particularly manic elation) and irritation are strongly associated with the left frontal pole, whereas melancholy, sadness and compassion are associated with the right frontal pole (generally all pro-social emotions). Ian McGilchrist writes - 'As usual it is not a matter of the right hemisphere versus the left hemisphere in the sense that one must be right and the other wrong, but the need for a judicious harmonising of them both. Each has its place. Nothing needs to be ruled out in the relationship between the hemispheres. But, as always, they are not symmetrical in value... the right hemisphere is engaged in social bonding and empathy, the left hemisphere in social rivalry and self-regard.'

The Left Hemisphere - excellent at tool manipulation, language and verbal reasoning

Mechanically-wise, McGilchrist explains 'relational arguments (A is to the left of B; B is to the left of C; therefore A is to the left of C) require right hemisphere involvement. Categorical arguments (all As are Bs; all Bs are Cs; therefore all As are Cs) require left hemisphere involvement, as do propositional arguments (if there is an A, then there is a B)... left hemisphere’s superiority for language stems from its being the hemisphere of representation, in which signs are substituted for experience'. Should a person suffer a left hemisphere stroke, the may struggle with language and motor impairments (especially of the right side of the body). McGilchrist writes 'Speech arose in humans in an area of the left frontal cortex, called Broca’s area, which lies just next to the area that controls movement of the right hand. Indeed it is widely thought that language developed, in part, from gesture. This speech area has been found to be activated even by grasp and manipulation, and is constantly involved in the production of meaningful gestures. Equally, restricting hand movements impairs verbal fluency'. Ideomotor (not knowing how to use objects) can arise as a consequence of left-brain damage.

As explained, the left brain handles propositional arguments but not relational arguments. This is because it is primarily linear and has the answer (e.g. true or false), and not spatial nor able to search for an answer. Thus, sign language is still left-hemisphere mediated. McGilchrist reveals 'tokens or symbols cannot escape being part of the real world in the right hemisphere, and the real world cannot escape becoming tokens or symbols in the left hemisphere. Thus subjects with their left hemisphere experimentally suppressed reported that the sun was so named ‘because it shines’, bread because it is ‘so tasty and fresh’, spaghetti because it’s ‘what you eat with cheese’. They couldn’t accept that objects might be renamed; the name was part of what they were. By contrast, with the right hemisphere suppressed, subjects took the view that names are entirely arbitrary.'

The left hemisphere provides us the the range of language used to help create mental maps, since it has 'a much more extensive vocabulary than the right, and more subtle and complex syntax. It extends vastly our power to map the world and to explore the complexities of the causal relationships between things. This is surely its raison d’être, and it is valuable to a predator, at least in simple circumstances...'' Grammer skills rely on left-brain functioning, since it is pattern and rule based. The left hemisphere finds predictability, familiarity and certainty appealing and tends therefore to treat many things as more certain than they are (to be more delusional). McGilchrist writes - 'the left hemisphere has precision, but it lacks the same intuitive sense of what it is actually doing, other than following rules and manipulating symbols.'

Illustrating the left-hemispheres tendency to relate categorically (A=B=C), even when detrimental, he points out the results of a simple experiment 'requiring the participant to predict which of two stimuli will appear on a given trial, say a green light or a red light, the isolated left hemisphere of split-brain patients attempted to distribute its responses in a way that matched the probability with which each stimulus appeared. So if it seemed that red came up two-thirds of the time, it would randomly predict red on two-thirds of occasions and green on the other third. That may sound smart, but it’s illogical. You don’t know ahead of time which individual stimulus will be which, and you end up scoring at chance level. The correct solution is to choose red every time, since it is always more likely. And this is exactly what the right hemisphere does, thus maximising the number of correct responses.'

People suffering Cotard's syndrome (also called walking corpse syndrome or Cotard's delusion) believe that parts of their body are missing, or even that they don't exist or are dead (leading some victims of the illness to go as far as cutting their wrists to prove they have no blood in them). Numerous studies have shown that 'Cotard’s delusion is often linked to right parietal, and possibly frontal and temporal, cortico-subcortical strokes or ischemia with left-sided sensory deficits including hemisensory loss and spatial neglect.' .

The left hemisphere is far from rational emotionally, and is prone to seeing things over mechanically. McGilchrist deduces 'While the left hemisphere is not a computer, it is an intermediary, an emissary – better at carrying out procedures than understanding their meaning.'

Indian neuroscientist Vilayanur Ramachandran, author of Phantoms in the Brain summed up in his book how sadness is not processed well by the left hemisphere - 'after right hemisphere strokes, patients tend to be blissfully unconcerned about their predicament, even mildly euphoric, because without the "emotional right hemisphere" they simply don't comprehend the magnitude of their loss. ( this is true even of patients who are aware of their paralysis).' By contrast, in cases of depression, 'inactivity is often especially pronounced in the left dorsolateral prefrontal cortex, while the right dorsolateral prefrontal cortex may also be too active'). Depression may be linked with a faltering left-hemisphere and a lack of elation, or excessive right hemisphere activity and is linked with a lack of dopamine (which the left hemisphere relies more heavily on than does the right hemisphere).

In an interview for the NY times Ramachandran revealed that he believed the left hemisphere's job was to impose 'consistency onto the story line. When something doesn't quite fit the script, you don't rip up the whole story and start from scratch. Rather, you deny or confabulate, to make the information fit the big picture. Far from being maladaptive, such everyday defense mechanisms keep the brain from being hounded into directionless indecision by the combinational explosion of possible stories that might be written from the material available to the senses'.

The right hemisphere - excellent at comprehending and expressing emotion; deciphering truth; processing speed and spatial skills

Whilst Ramachandran said of the hemispheres that 'the left's job is to create a model and maintain it at all costs', he equally reflected that 'the right's job is to detect anomalies. When anomalous information reaches a certain threshold, its job is to force the left hemisphere to revise the entire model and start from scratch. The left tries to cling. The right tries to force paradigm shifts'. This makes the right hemisphere a fantastic truth-teller and lie-detector, the original ‘devil’s advocate’.

McGilchrist draws from two recent studies that pinpoint why this is the case - 'One of the most recently evolved areas of the brain, the right dorsolateral prefrontal cortex, plays an especially critical role in counterbalancing this (tendency of the left hemisphere to make hasty conclusions). This part of the brain has repeatedly been shown to be crucial to judgments where there are either conflicts between the facts being put forward and what we know from experience, or between what we know from experience and what reasoning suggests.' In short, the right hemisphere explains the non-conformist in us, that searches for discrepancies when we're fed lies, that takes responsibility for failures when self-caused and that takes little for granted, acting on information as if it is relatively new and complex, with fewer prejudices.

It has been said the left hemisphere excels verbally, and the right at deciphering truth. It is no surprise that the latest studies show that people with aphasia – a loss in language ability resulting from a stroke or other type of brain damage – 'appear to have a significant advantage in spotting liars, particular when the untruths are given away by changes in facial expression.'

However, language is not all left-hemisphere dominated. The right hemisphere is more receptive and reactive to three of the most important aspects of language - 'metaphor, ‘prosody’ (the music of the voice, its infection and intonation) and ‘pragmatics’ (the understanding of an utterance as a whole in its real-world context)'. Naturally, body-language is most understood by the right-hemisphere and excessive deliberate concentration on it may lead to accidentally worse interpretations (the sub-conscious is always at play and hopefully balanced by the right hemisphere, but deliberate conscious attempts to interpret body language may be more vulnerable to left-hemispheric prejudices and known-biases). It has been shown that the 'reception of non-verbal human sounds, including laughing, but also crying and shrieking, are strongly lateralised to the right hemisphere' and though 'perhaps surprisingly to some, the right hemisphere that has the better intuitive sense of numbers and their relative size.'

Moreover, 'right hemisphere-damaged patients showed much greater impairment on simple reaction times than left hemisphere-damaged patients.' Finally, McGilchrist states that 'we know that greater right than left parietal activation at rest predicts a better performance on visuo-spatial reasoning' (and greater left with verbal reasoning), and that's this partially explain why the right hemisphere can solve problems more adequately - 'When it comes to problem-solving, visual thinking is far more important than verbal'. From the left hemisphere’s point of view he writes - 'imagination, like metaphor and myth, is a species of lying: from the right hemisphere’s point of view, it is, like metaphor and myth, necessary for access to truth… if we lose the sense of just how much we do not know, we lose understanding of even the little that we do know… Our imagination is stretched to the utmost, not, as in fiction, to imagine things which are not really there, but just to comprehend those things which are there.’ Ideas generally require the imagination both to be made and comprehended.

Note, the 'right ventromedial prefrontal cortex is dysfunctional in psychopaths, who do not have the usual feelings for others.'

Signs from nature that we connect primarily through our right hemisphere

Since it is known the right hemisphere has greater control over the left side of the body including the left half of the face, researchers have deduced that the left hemiface is more expressive emotionally than the right. Research dating from 1984 titled 'Face touching in monkeys, apes and man' published by Stuart Dimond and Rashida Harries showed that whilst 'monkeys show little if any face touching, 'Gorillas, orang-utans and chimpanzees show face-touching comparable to man. Left-hand face touching was superior to right- hand touching for both apes and humans.' Equally, bottle-nose dolphins - known for their emotional intelligence, 'tend to stroke other dolphins more with their left flipper', paralleling humans, gorillas and chimps. Moreover, it is known that human mothers tend to cradle their infants to their left just like how 'creatures as various as whales, walruses and flying foxes prefer to keep their young to the left of them'.

A personal anecdote of a Left-Brain Stroke

Dr. Jill Bolte Taylor was a Harvard trained and published neuroscientist when she experienced a major hemorrhage in the left half of her brain in 1996. She subsequently recovered and wrote an autobiographical book published in 2008, titled - 'My Stroke of Insight: A Brain Scientistʼs Personal Journey' where she recounted the immediate experience of losing her left-brain functioning in the following passage:

'Imagine, if you will, what it would feel like to have each of your natural faculties systematically peeled away from your consciousness. First, imagine you lose your ability to make sense of sound coming in through your ears. You are not deaf, you simply hear all sound as chaos and noise. Second, remove your ability to see the defined forms of any objects in your space. You are not blind, you simply cannot see three-dimensionally, or identify color. You have no ability to track an object in motion or distinguish clear boundaries between objects. In addition, common smells become so amplified that they overwhelm you, making it difficult for you to catch your breath.

No longer capable of perceiving temperature, vibration, pain, or proprioception (position of your limbs), your awareness of your physical boundaries shift. The essence of your energy expands as it blends with the energy around you, and you sense that you are as big as the universe. Those little voices inside your head, reminding you of who you are and where you live, become silent. You lose memory connection to your old emotional self and the richness of this moment, right here, right now, captivates your perception. Everything, including the life force you are, radiates pure energy. With childlike curiosity, your heart soars in peace and your mind explores new ways of swimming in a sea of euphoria. Then ask yourself, how motivated would you be to come back to a highly structured routine?'

How victims of right hemisphere damage can be affected

Social problems - getting context and subtleties

One of the most considerably problematic signs of patients with right-hemisphere deficits is a failure to understand nuances and the meanings behind questions and of narratives such as films, books and in conversations. Typically and funnily enough this is usually accompanied by a total lack of ability in acknowledging that they do not know that they missed the plot, or that they did not know how to answer a question in any meaningful reply. As Penelope S. Myers, author of ' Right Hemisphere Damage: Disorders of Communication and Cognition' described how her patients respond to straightforward questions - 'They wended their way through a maze of disassociated detail, seemingly incapable of filtering out unnecessary information. Although they had at their disposal all the components of a narrative, they could not actually assemble them into a

narrative.' German neuroscientist and psychiatrist Walther Poppelreuter described how a 22 year old shoulder Robert Spyra who suffered a right posterior shrapnel injury, when asked to describe a film, 'reported a large number of correctly observed individual scenes without any grasp of the overall plot structure’. Other researchers reported how upon showing a patient a cartoon, the patient asked them - 'The first thing I’d like to know is how the elephant got up that tree' with total sincerity, and another that upon asking a patient how they feel, he would be answered 'with my hands' without a trace of humor.

Flattened Space (Linearity)

We see the world three-dimensionally principally as a result of the right hemisphere so when a person suffers hemispheric damage on that side, the world loses its shapes and becomes more linear. If asked to draw a cube, the individual with only a functioning left hemisphere may draw 6 lines, knowing a cube to have six sides but otherwise would struggle with the actual dimensions aspect. Consider the drawings of a commissurotomy split brain patient five months after an operation, copying a model with either hand (he still had input from the right hemisphere when drawing with his left) -

Equally consider the drawings of a cyclist by the same artist before and after right hemisphere strokes and how much more linear his drawings become.

Some injuries may make it impossible for victims to put things together correctly if there's too much damage to the right hemisphere - below, is a recorded attempt to assemble mannequin from parts by a person afflicted with a right posterior tumor-

Asomatognosia - The inability to acknowledge parts of the embodied self

This condition is 'estimated to occur in 90% of all right hemisphere strokes, and in 100 cases examined by Feinberg, who has made the most extensive investigations of the phenomenon to date, it never once followed a left hemisphere stroke, always a right hemisphere one'. Hécaen & de Ajuriaguerra described the behavior of a patient with a right posterior parietal stroke, who suffered from Asomatognosia:

‘Give me your hand’: gives her right hand. ‘Give me the other one?’: withdraws her right hand from the examiner’s and places it in his other hand. If one repeats the request, she

transfers her right hand from one hand to the other, making no effort to offer her left hand. When she is confronted with her left hand, and asked whose hand it is, she replies: ‘it’s

your right hand’.

The bizarre symptoms of Hemineglect - denial of left side of space

Neuropsychologist Edoardo Bisiach detailed an even more bizarre symptom of most (up to 80% when in a critical state) left brain strokes and unilateral injuries. He wrote that 'neglect patients not only do not see stimuli presented in the contralateral half of space, but behave as if that half of space did not exist and never had existed. Indeed, the most astonishing aspect of neglect is perhaps this: patients suffering from it, not only are unable to perceive the left side of space, but are not even able to conceive it.' In this way, they exemplify how left-brain damaged individuals can suffer completely from denial of their deficiencies, even when their issues are logically proven to them.

When Bisiach asked two patients with hemineglect to 'picture in their imagination a scene that was familiar to them – the main square in Milan, the Piazza del Duomo – as if they were looking toward the west front of the Cathedral' the patients could only manage to accurately describe 'the buildings that lay to the right along the south side of the square'. They described 'nothing' or 'almost nothing' on the other side. Then they were asked 'to imagine they were at the other end of the square, standing with the Cathedral behind them, facing the other way'. Bisiach found that his patients 'now named the very places they had previously neglected but omitted those that had been previously recalled'. Having proved their memory was not a problem, neither patient managed to merge the two sides into a complete picture, only being able to imagine the buildings facing their left side yet 'they were not apparently dismayed by this in the least.'

References

(1) The Matter With Things: Our Brains, Our Delusions, and the Unmaking of the World, Iain McGilchrist, 2021

(2) My Stroke of Insight: A Brain Scientistʼs Personal Journey, 2008, Jill Bolte Taylor