But according to Webb, a child and adolescent psychiatry fellow at the Yale Child Study Center with a particular interest in biomarkers of psychosis, “a striking of 40% of those with schizophrenia or schizoaffective disorder are left-handed.”
More left-handed people are found among schizophrenics than in the general population. Brain researcher Marco Hirnstein believes that this is due to common genes between hand preference and the disease.
Researchers believe hand preference may have to do with the developmental differences between the right and left hemispheres of the brain. The right hemisphere controls movement on the left side of the body, while the left hemisphere controls movement on the right side of the body.
A 2011 study from the American College of Chest Physicians suggested that left handers have significantly higher chances of developing periodic limb movement disorder (PLMD). This disorder is characterized by involuntary, repetitive limb movements that happen while you sleep, resulting in disrupted sleep cycles.
Left-handedness and longevity
In addition, some diseases associated with left-handedness are relatively rare and there is no evidence that left-handedness is associated with increased risk of common diseases such as malignancy, cerebrovascular and cardiovascular diseases.
Handedness was also linked to predisposition to neuropsychiatric disorders, supports the “plethora of literature” that already points to an association between left-handedness and psychiatric disorders, and particularly schizophrenia, the authors stated.
Wright and Hardie (2012) found that left-handers reported higher levels of state anxiety but there was no difference in trait anxiety. They also demonstrated that when Trait Anxiety was controlled for, left-handers still showed a higher level of state anxiety compared to right-handers.
Left-handed and ambidextrous people are more susceptible to negative emotions, including anger. A small study published last year in the Journal of Nervous and Mental Disease found that the brains of lefties process emotions differently than those of righties, with more communication between the brain's two halves.
Left-handed people are said to be good at complex reasoning, resulting in a high number of lefty Noble Prize winners, writers, artists, musicians, architects and mathematicians. According to research published in the American Journal of Psychology, lefties appear to be better at divergent thinking.
In fact, one of the more unusual hypotheses to explain the rarity of left-handedness is that a genetic mutation in our distant past caused the language centres of the human brain to shift to the left hemisphere, effectively causing right-handedness to dominate, Alasdair Wilkins explains for io9 back in 2011.
Left-handedness was associated with differences in brain asymmetry in areas related to working memory, language, hand control and vision. Some of these brain areas were linked to specific genes. Scientists have long been fascinated by left-handedness.
Lefties get angrier
A study in The Journal of Nervous and Mental Disease suggested that those who are left-handed are more prone to negative emotions. It also found that when processing emotions, lefties have a greater imbalance in activity between the left and right brains.
Researchers have identified, for the first time, the genetic differences between right-handed and left-handed people. In left-handed people, both sides of the brain tend to communicate more effectively. This means that left-handed people may have superior language and verbal ability.
The risk for schizophrenia has been found to be somewhat higher in men than in women, with the incidence risk ratio being 1.3–1.4. Schizophrenia tends to develop later in women, but there do not appear to be any differences between men and women in the earliest symptoms and signs during the prodromal phase.
While some reasons for the differences in thinking and functioning may be genetic and anatomical, left-handedness is behavioral as well. Things left-handers do differently are often influenced by the societal implications of having a dominant hand that differs from the general public.
The idea that left-handed people are more intelligent than right-handers is a myth. There have been lefty geniuses in history like Leonardo da Vinci, but this is not part of a larger pattern. If anything, the opposite is true.
McManus which found that the Netherlands has one of the world's highest prevalences of left-handedness at 13.23 percent. The United States isn't far behind with a rate of 13.1 percent while neighboring Canada has 12.8 percent. Elsewhere, rates of left-handedness are far lower and China is a good example.
Other issues plaguing left-handed school kids include learning to tie their shoes, learning to use a ruler, learning how to hold a pencil, operating right-handed pencil sharpeners, and right-handed sports equipment.
Sinistrophobia is the fear of left-handedness or things on the left side.
THIS STUDY TESTED WHETHER LEFT-HANDED JUVENILES ARE OVERREPRESENTED AMONG VIOLENT JUVENILE OFFENDERS AND FOUND THAT LEFT-HANDED OFFENDERS SCORED LOWER THAN RIGHT-HANDERS ON THE VIOLENCE SCALE.
Lefties Hear Speeches Differently
People who use their left hands when listening may more easily hear slowly-changing sounds than those who use their right hands, according to a study from Georgetown University Medical Center.
On the flip side, lefties have some disadvantages too.
Some studies show that left-handed people showed an imbalance in processing emotions with their left and right hemispheres of their brain. Left-handed people have a higher risk of brain disorders like schizophrenia, dyslexia or hyperactivity disorders.
In a review of 12 studies including a total of 497 individuals diagnosed with ASD, Rysstad and Pedersen (2016) found 16% left-handers and 44% mixed-handers, giving a total of 60% non-right-handers.
The prenatal environment and cultural influences may play a role. Like many complex traits, handedness does not have a simple pattern of inheritance. Children of left-handed parents are more likely to be left-handed than are children of right-handed parents.