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Psychology Neuropsychology

Side Effects

How Left-Brain Right-Brain Differences Shape Everyday Behaviour

by (author) Lorin J. Elias

Dundurn Press
Initial publish date
Aug 2022
Neuropsychology, General, Neuroscience
  • eBook

    Publish Date
    Aug 2022
    List Price
  • Paperback / softback

    Publish Date
    Aug 2022
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Understanding how right-brain and left-brain differences influence our habits, thoughts, and actions.

Human behaviour is lopsided. When cradling a newborn child, most of us cradle the infant to the left. When posing for a portrait, we tend to put our left cheek forward. When kissing a lover, we usually tilt our head to the right. Why is our behaviour so lopsided and what does this teach us about our brains? How have humans instinctively used this information to make our images more attractive and impactful? Can knowing how left-brain right-brain differences shape our opinions, tendencies, and attitudes help us make better choices in art, architecture, advertising, or even athletics?

Side Effects delves into how lateral biases in our brains influence everyday behaviour and how being aware of these biases can be to our advantage.

About the author

Lorin J. Elias, Ph.D., is a professor of psychology at the University of Saskatchewan. He completed his Ph.D. in behavioural neuroscience at the University of Waterloo and has been studying left-brain right-brain differences for over twenty years. Lorin lives in Saskatoon.


Lorin J. Elias' profile page

Excerpt: Side Effects: How Left-Brain Right-Brain Differences Shape Everyday Behaviour (by (author) Lorin J. Elias)


I think of my body as a side effect of my mind.
— Carrie Fisher

Human behaviour is lopsided. Our bodies are relatively symmetrical, at least on the outside, but the way we behave is not. Chances are, your left hand and right hand don’t look much different from each other, yet almost 90 percent of us prefer to use the right for writing, throwing, and almost any activity requiring considerable skill. However, when cradling a newborn child, most of us cradle the infant to the left. When posing for a portrait, whether hand-painted in the 16th century or a modern selfie on Instagram, we tend to put our left cheek forward. When kissing a lover, we tend to tilt our head to the right. Why is our behaviour so lopsided and what does this teach us about our brains? How can we use this information to make our selfies more attractive when posting them to our online dating profiles, or how can we Photoshop our political advertisements to make the candidate more appealing to a particular political demographic? Can knowing how left-brain right-brain differences shape our opinions, tendencies, and attitudes help us make better choices in art, architecture, advertising, or even athletics? By the end of this book, you will see how lateral biases in our brains influence our everyday behaviour and how you can use this information to your advantage.

The functional differences between the two sides of the brain are easy to detect in a scientific laboratory, in a hospital’s brain scanner, or from an individual’s behaviour after a one-sided brain injury or brain surgery. However, these left-right differences are also readily observable in normal people as they simply go about their daily routines. Our lopsided behaviour is hidden in plain sight.

Some of our left-right differences are very strong, consistent, and old. For example, 90 percent of us favour the right hand, and it doesn’t matter whether you are male or female, from Malaysia or France. Furthermore, our species has been right-hand dominant for more than 50 centuries, according to analyses of ancient artifacts and artworks. Other strong lateral preferences are more recent, only hundreds of years old, such as posing biases in portraits. If we take a careful look at religious artworks depicting the Crucifixion of Jesus, we find that 90 percent of them depict Jesus turning his head to the right and putting his left cheek forward. Our lateral posing biases for cradling babies are also quite old, but they’re nowhere near as strong — about 70 percent leftward — as our population-level hand preferences.

The lopsided behaviour surveyed throughout this book relates to our underlying left-right brain differences. Everyone’s brain is unique. Just like the unique face each person displays on the outside of their head, most everyone has the same parts inside their skull, with the same general shape, location, and function. But each brain is unique. All of the left-right differences encountered in this book are at the population level. In other words, the biases discussed here are trends that apply to a large group of people but not necessarily to every individual within the group. Take handedness, for instance. There is a population-level bias toward right-handedness, but some people are left-handed. We know that 90 percent of people are right-handed but that doesn’t mean there is anything wrong or fundamentally different with each left-hander in the world. The same holds true for other individual differences in brain lateralization. The left side of the brain is dominant for language in 90 percent of us, but that doesn’t mean the 10 percent with right hemispheric language are any less proficient with the spoken or written word.

In some cases, these individual differences in lopsided behaviour can be revealing. For example, most new mothers cradle their infants to the left, but rightward cradling is more common among mothers with depression. If you prefer to cradle your little one to the right, does that mean you are depressed? Absolutely not. However, in a population of people who prefer rightward cradling, depression is more common in the group compared to those who cradle to the left. This book is an exploration of population-level and group trends, not individual diagnoses or analyses.

While I am issuing disclaimers, one more note of caution is necessary before we proceed. The left-right differences surveyed here are relative, not absolute. I’m a member of the right-handed majority, but my left hand is not completely useless. I routinely employ it for relatively unskilled tasks, such as picking up and carrying objects, and I can use my left hand to shoot a basketball well enough to win the occasional game of H-O-R-S-E. Similarly, I know from a functional magnetic resonance imaging (fMRI) scan that the left hemisphere of my brain is dominant for language. However, that does not make my right hemisphere functionally illiterate. It can read and understand words in several languages, but not with the same speed, fluidity, and nuance — particularly when word order is important — as my left hemisphere. As I said, the differences between the hemispheres are relative, not absolute. Even if the differences were absolute — and they are not! — the two hemispheres of the brain are interconnected with more than 250 million projections from one side to the other by an impressive white-matter structure called the corpus callosum.

The two hemispheres of the brain collaborate to form perceptions, memories, and even biases. Stating that one half or the other is solely responsible for any of those things is more than an oversimplification; it is usually wrong. Consider this example: my teenage daughter, Mileva, walks into the living room, and I exclaim, “Nice shoes!” Her left hemisphere is probably more proficient at decoding spoken words, and on its own, it might interpret my statement as a compliment. However, what if I used a sarcastic tone when saying those two words? “Niiiiice shoes!” The pitch and tone decoding expertise typically dominated by the right hemisphere of the brain would detect that shift in meaning, and Mileva could then scoff at her father’s lack of fashion sense as she leaves the room.

Disclaimers aside, there are many structural, chemical, and functional differences at the population level between the two halves of the brain. The right hemisphere tends to be larger and heavier and contains more white matter (brain cells covered in a fatty insulation called myelin) than the left and is more diffusely organized and interconnected. In comparison, the left hemisphere is smaller and denser and contains a higher proportion of grey matter (brain cells). If we take a typical brain out of the skull and look at it from above, it tends to exhibit a counter-clockwise torque, with the frontal lobe of the right hemisphere extending farther forward and the occipital (rearmost) portion of the left hemisphere extending farther back (see Fig. 1). There are also many more lateral differences within the hemispheres, such as the planum temporale (a structure associated with language processing) normally being larger in the left hemisphere. These are just the physical differences. This book is really about the functional differences.

The most well-known functional difference is left hemisphere dominance for language. We know from studies of brain injuries, brain surgeries, and functional brain imaging that the left brain dominates language for 90 percent of us. It also excels at perceiving word order (i.e., syntax) to make meaning of phrases (consider “dog bites man” versus “man bites dog”), perceiving rhythm in music, performing logical ordering, and planning sequences of movements. Conversely, the right hemisphere excels at perceiving emotion (especially negative emotion), spatial information, pitch/melody in music, facial recognition, tone of voice in speech, and perceiving themes in pictures, sounds, and spaces.

One of the most striking and puzzling features of the vertebrate nervous system is its contralateral organization. For every vertebrate animal known (even Agnathans, jawless fish from the Cambrian period), but no known invertebrates, the right side of the brain controls the left side of the body, and the left side of the brain controls the right side of the body. The same reversal holds true for information coming into the nervous system. A touch on the left hand is perceived by the right hemisphere of the brain and vice versa. For some of our senses, this crossover is more complete than for others. For visual information, almost all of it on the left side (not through the left eye, but the data from the left side going to both eyes) projects to the right hemisphere (see Fig. 2). Hearing is a little different, with about 70 percent of the information from the left ear projecting to the right hemisphere of the brain. Why is our nervous system crossed over? I have no idea. It just is.

As you read this book, you are going to get your lefts and rights confused at times, but that won’t be your fault. It doesn’t mean there is something wrong with you. I will require some fancy mental gymnastics from you at times, and with the help of a picture or two, I am confident that we can navigate these lefts and rights together. Fig. 2, which shows the crossover in the visual system, seems simple enough: left space goes to right brain and vice versa. However, when I start to describe how the right hemisphere’s specialization for facial recognition is responsible for the left-cheek bias for selfies taken in the mirror, you have to imagine a person’s face centred where the red/green area is, imagine which half of the face is in which space for two people facing each other, and then reverse your lefts and rights yet again in your mind because the scenario being discussed is someone looking at him or herself in the mirror!

This book is organized in a way that presents our lateral biases one at a time, which can give the impression that they are always independent of one another, but they are not. For example, hand preferences (see Chapter 1) are strongly related to our lateral preferences for feet, ears, and eyes (see Chapter 2). The posing biases in portraiture (see Chapter 6) are also related to the lighting biases (see Chapter 7) we glimpse in the same pieces of artwork. This doesn’t mean that one bias necessarily causes the other, but just because the biases are discussed in separate chapters doesn’t mean they are discrete, independent phenomena. Many of them connect to one another, and the Afterword is dedicated to stringing those together once we have examined each bias on its own.