Left-handed people are more likely to neurocognitive and psychological disorders such as dyslexia, schizophrenia, and attention deficit hyper activity disorder.
Left-handed people have been the subject of curiosity, the butt of jokes, and been forced to use right-handed scissors for years. However, new research is beginning to uncover a deeper understanding of why some people opt to write with one and, and some opt for the other.
In addition to hands, people can also be left or right footed or even be left or right-eyed, a laterality known as ocular dominance. While this is more or left common knowledge, experts are now saying that laterality is a window into how the brain is wired. A bit more esoteric is the fact that neurocognitive and psychological disorders are more common in left-handed people – conditions such as dyslexia, schizophrenia, and ADHD as well.
Ambidextrous individuals, who make up approximately 1% of the population, are even more prone to these conditions.
The cause of laterality is not fully understood, but genetics have been identified as a factor, but even the laterality of identical twins is not always identical. Researchers have also identified environmental factors – stress in particular – in the womb as a major factor in determining laterality.
For example, children who were born to older mothers are more likely to be lefties, and same with kids with lower birthweights.
A literature review in the journal Neuropsychologia attributed approximately 25% of laterality variability is due to genentics.
More Creative, Paid Less
Despite popular perception, studies indicate that there is no discrepancy between the IQ scores of righties versus lefties. However, some evidence suggests that lefties may indeed best the right-handed majority when it comes to divergent thinking – a key element of creativity.
Harvard University recently surveyed and assessed income levels and laterality to reveal that on average, left-handed individuals made on average 10% less than right-handed people.
The exact reason for this financial discrepancy is not fully understood, but it may have something to do with recent research highlighting the greater risk faced by lefties of psychiatric and developmental disorders. While approximately 10% of the world is left-handed, they are clearly overrepresented in disorders such as schizophrenia, dyslexia, and ADHD where they make up 20% of the population.
The underlying cause for this remains unclear, but scientists suspect that it might be due to a concept known as brain lateralization. As you may already know, the brain is comprised of two halves, and just as we favor one hand over the other, we may favor one half of our brain over the other.
Right or Left Brained
Typically right-handed people rely primarily on the left side of their brain, but this doesn’t hold true for lefties. Approximately 70% of those who are left-handed also are left-brain dominant, but the other 30% rely more on their right brain, and it is in these individuals where impaired learning and brain disorders are of a higher risk.
Dr. Alina Rodriguez, a professor of psychology at Mid Sweden University in Östersund, Sweden studied handedness, brain development and ADHD. In a 2008 study she conducted, she discovered that left-handed and ambidextrous children were at greater risk of language learning in additional to ADHD-like symptoms. In a separate study published in Pediatrics, Dr. Rodriguez strengthened those findings in a sample of over 8000 Finnish children.
Part of the reason why more is not known about left-handed individuals is that they are often purposefully excluded from participating in studies as the wiring of their brains is known to be different, and therefore can complicate findings.
While these results can certainly helpful in understanding the intricacies of the brain, experts are suggesting the most actionable implications are using left-handedness or being ambidextrous as a risk factor for developmental conditions or behavioral difficulties. Therefore, should this or other early warning signs of ADHD arise, they should be a call for an early evaluation for this and other conditions.