Approximately 10% of the global population is left-handed. For a long time, being left-handed was seen as abnormal or negative. However, research has shown that being left-handed changes how the brain functions in some unique and potentially beneficial ways. In this article, we will explore what science tells us about the differences between left-handed and right-handed brains.
Brain Hemispheres
The human brain is divided into two hemispheres, the left and the right. Each hemisphere controls the opposite side of the body. So the left hemisphere controls the right side of the body, and vice versa. In most people, the left hemisphere is dominant. It controls primary functions like language and logical processing. This is true for around 95% of right-handed people and 70% of left-handed people. However, left-handers are more likely to have co-dominance of both hemispheres or right hemisphere dominance.
This difference in laterality leads to some changes in how the brains of lefties function. Left-handers tend to utilize both hemispheres for language processing more equally. This co-dominance may help left-handed people process language faster and allows for more flexible thinking. However, it could also cause slightly less coordinated processing between hemispheres overall.
Corpus Callosum
The corpus callosum is a thick nerve tract that connects the left and right hemispheres of the brain. It allows the hemispheres to communicate and work together. Some studies have found that the corpus callosum tends to be larger in left-handed people. This may allow for faster transfer of information between hemispheres and better connectivity.
In one study researchers analyzed over 100 brain scans and found that the corpus callosum was an average of 11% larger in left-handers. Other studies have had similar findings, with left-handers having 3-5% larger corpus callosums on average. A larger corpus callosum may partly explain the language processing advantages and co-dominance of brain hemispheres in lefties.
Cerebral Cortex
The cerebral cortex is the outer folded layer of the brain that handles complex cognitive functions. In left-handers, regions in the left and right cerebral cortex often have more symmetrical activations. In right-handers, there is typically stronger left hemisphere activation, particularly for functions like language. Greater symmetry between cortical hemispheres may be beneficial for lefties’ co-dominance and flexible thinking abilities.
There are also some differences in cortical structure. One MRI study found that in left-handers, regions behind the central sulcus have larger gray matter volume. These areas are linked to processing sensory input. Having more gray matter could lead to advantages in visual-spatial skills for some left-handed people.
White Matter
White matter in the brain refers to myelinated axons that pass nerve signals between neurons. Multiple neuroimaging studies have shown increased white matter connectivity in the brains of left-handers, particularly in inter-hemispheric connections. This suggests lefties may have faster communication between brain hemispheres along white matter tracts like the corpus callosum.
One Dutch brain imaging study found greater structural connectivity in left-handers between regions linked to visuospatial, language, and executive functions. The increased white matter in lefties may facilitate cognitive advantages in these domains.
Prefrontal Cortex
The prefrontal cortex handles higher-level executive functions like planning, decision-making, and inhibitory control. Some research using EEG scans indicates left-handers may have more developed prefrontal regions. One study found left-handers had increased prefrontal cortex activity while completing complex problem-solving tasks.
Enhanced prefrontal activation could be linked to advantages lefties exhibit on divergent thinking, problem solving, and concept formation tasks in some studies. However, other studies have found no significant difference in executive function between left and right-handers. More research is still needed in this area.
Parietal Lobe
The parietal lobe integrates sensory information and links it to motor control. Neuroimaging studies have found some structural and functional differences in the parietal lobes of left-handers. Left-handers often have better connectivity between parietal regions.
Some studies also indicate the parietal lobe is larger in left-handers, which may be tied to visuospatial processing advantages. The parietal lobe activation linked to language tends to be more bilateral in lefties as well. Altogether, this can lead to enhanced sensorimotor skills with the left hand in left-handers.
Dyslexia and Schizophrenia
Being left-handed comes with a slightly increased risk of conditions like dyslexia and schizophrenia. Left-handers are twice as likely to develop schizophrenia. Around 40% of dyslexics are left-handed, compared to just 10% of the general population.
The reasons are unclear, but may be tied to differences in brain hemispheric dominance. Dysfunction in hemispheric connections could increase susceptibility. However, increased risk does not mean causation. Most left-handers do not develop psychological disorders and differences like dyslexia may be linked to brain advantages as well as disadvantages.
Cognitive Advantages
While results vary across studies, research suggests left-handers may outperform right-handers in some cognitive domains including:
- Verbal processing
- Multitasking
- Creativity and divergent thinking
- Visuospatial skills
- Concept formation
- Pattern recognition
- Memory recall
These cognitive advantages may be subtle on an individual level. However, on a population basis, they indicate enhancements in key functions like language, creativity, and visual-spatial skills for left-handers on average. The differences in brain development likely underpin these cognitive trends.
Causes
So why does left-handedness develop in the first place? Handedness likely arises from a complex interplay of genetic and environmental factors. Here are some of the main theories on what leads to left-hand dominance:
- Genetics – specific genes may increase likelihood of left-handedness. If one identical twin is left-handed, there is a 76% chance the other twin will also be left-handed.
- Prenatal hormone exposure – greater exposure to testosterone in uterus could shift brain development. This may make left-handedness more likely.
- Developmental instability – variations in genes, hormones, or environment during fetal development may cause atypical lateralization.
- Birth stress – trauma during birth process may shift brain structure and handedness.
- Ultrasound exposure – one unproven theory links increased left-handedness to widespread use of ultrasound scanning during pregnancy.
While the causes are not fully understood, it appears left-handedness arises very early, either prenatally or perinatally. The differences in brain structure and function probably stem from genetic and developmental factors influencing hemispheric dominance before birth.
Learning and Environment
Does being left-handed affect learning abilities or how the brain takes in new information? Overall the answer seems to be no. While there are subtle structural and functional brain differences, lefties do not learn in a fundamentally different way. However, social and environmental pressures may shape left-handed learning in some ways.
In many cultures, right-handedness is the dominant norm. Things like desks, scissors, and notebooks are designed for the right-handed majority. For lefties, this can cause minor frustrations and difficulties using these tools designed for right-handers. However, left-handers adapt easily. While awkward at first, lefties learn to use right-handed items proficiently.
One area where lefties may struggle more is handwriting. Many left-handers hold their pen or pencil in a “hook” position to see what they are writing. Smearing ink and hand cramps are also common complaints. Proper posture and pen grip can help lefties improve handwriting legibility.
Left-handed people are also more prone to mirror writing, forming letters and words backwards. This may further mix up handwriting. While messy writing can be frustrating, it does not indicate any disorder or problem. With practice, lefties can develop excellent penmanship.
Sports and Coordination
Does being left-handed make you better at sports? There are some interesting links between left-handedness and athleticism. For starters, lefties may have enhanced motor skills and hand-eye coordination with their dominant left hand. Around 25% of MLB baseball players are left-handed, compared to just 10% of the general population.
In sports like baseball, fencing, boxing, cricket, and tennis, being left-handed can provide a strategic advantage. Lefties’ unconventional movements and swings can bewilder opponents. However, the same is true when right-handers face lefties. While left-handedness provides some unique traits, overall evidence does not show better fitness or sports performance in lefties across the board.
Everyday Challenges
While left-handedness is not considered abnormal anymore, lefties still face some daily frustrations living in a right-handed world. Beyond just using right-handed tools, lefties have to adapt to other social conventions.
Examples include shaking hands, taking notes, using a computer mouse, playing card games dealing out cards, using a manual can opener, playing musical instruments like guitars, operating a manual gear shift in a car, and sitting in right-handed desks at school. Lefties learn to live with these minor hassles, even if they seem silly and unfair.
On top of adaptations, left-handed people also deal with negative cultural stigma in some places. Historically, left-handedness has been seen as a sign of defiance, clumsiness, or even evil. Thankfully such superstitions have subsided in most modern societies. But residues remain in some language constructs that equate “right” with correctness and goodness.
Famous Left-Handers
While only a small minority of people, left-handers have made huge contributions to the arts and sciences. Here are just a few of the many influential historical and modern figures who are or were left-handed:
- Leonardo da Vinci
- Michelangelo
- Raphael
- Marie Curie
- Nikola Tesla
- Isaac Newton
- Paul McCartney
- Jimi Hendrix
- Lewis Carroll
- Mark Twain
- Babe Ruth
- Herbert Hoover
- Julia Roberts
- Oprah Winfrey
- Bill Gates
- Barack Obama
This list shows how left-handedness does not hinder success or achievement. The brains of famous lefties like Einstein and da Vinci may even have been enhanced in creativity and other cognitive functions.
Conclusion
In summary, being left-handed shapes the structure and function of the brain in subtle but important ways. Lefties exhibit greater symmetry between brain hemispheres and enhanced connectivity overall. This leads to advantages in some cognitive skills like language, creativity, problem-solving and visual-spatial abilities. Genetic and developmental factors cause these brain differences, which begin arising very early.
While left-handers’ brains work a little differently, lefties face no fundamental learning disabilities. They may struggle more with handwriting but otherwise take in new information the same as right-handers. Left-handedness also provides some uniqueness in sports and activities. However, lefties still have to adapt to live in a right-handed world.
Rather than a hindrance, left-handedness represents an alternative wiring of the brain that opens up different gifts and perspectives. Famous left-handed intellectuals, artists, and leaders show how lefties can achieve just as much, if not more, than their right-handed counterparts.