Left-handed people (which we’ll call “left-handed” for brevity) are people who write with their left hand or are physically in control of the left side of their body. Although they make up only about 10% of the population, they make up just as much 40% of cases of psychotic disorders Like schizophrenia. These are some of the most serious types of mental illness, characterized by hallucinations, strange beliefs, and a loss of contact with reality. Why leftists are more likely to develop mental illness?
To answer this question, it is helpful to understand why most people are right or left Primarily, how the use of hands relates to brain development, structure and function.
Why are we right-handed or left-handed in the first place?
Overlap—that is, the localization of a function or behavior to one side of the body or brain—occurs across species. For example, some types of Spiders primarily use their left legs More when dealing with prayer, and Honey bees primarily use their right eye When learning food associations. We humans use the right hand 90% of the time. Since at least the Paleolithic eramore than 10,000 years ago.
But why are we being set aside in the first place? In short, lateral selection is perhaps useful because it makes our brains more specialized and efficient by creating ‘areas of expertise’.
Just as with most complex business organizations, the human brain is made up of multiple areas with different functions. In general, the human brain is divided into the left and right hemispheres, and each hemisphere in turn participates in Various functions.
This separation allows efficiency. Grouping related functions together allows for specialization, reduced redundancy with other brain regions, and literally reduce space That relevant nerve signals must be transmitted to communicate. Lateral brains are generally more adept at various responsibilities and are private Adept at accomplishing simultaneous tasks – Like searching for food while observing predators.
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In particular, the right hemisphere appears to specialize in broader processes such as integrating visual information, while the left hemisphere is more involved in language and motor control. Since the left hemisphere tends to control the right side of the body, most people use the right hand.
Why do most people use the right hand
Lateral brains may help make individuals more efficient and successful. But why does an entire population group tend to be sideways in the same direction? The lateral division appears to be at the population level – so that everyone tends to be left-handed or right-handed – Improve social coordination.
The idea is that when most people are right-handed, we’re better able to predict each other’s behaviors – from hand to handshake, to which way to design the scissors, to which way Turn your head while kissing. For example, redwood ants mainly use the correct antenna when food exchangewhich reduces errors in contact with the antennas.
Explanation of 10% left-handed
If right-handed use is beneficial, evolutionary theory would predict that over time, left-handers would be less likely to pass on their genes and eventually die. So why have rates of left-handedness remained constant for thousands of years? There are two reasons.
First, genetics. according to combat hypothesisLefties are better at fighting and other competitions. And so, they keep going left gene Despite the potential deficit in other areas. Indeed, about 25% of handedness is hereditary, and left-handedness is more likely than right elite athletes.
Second, environmental factors contribute to becoming left-handed, such as brain injuries and early life stressors. For example, the research found that Lesions of the brain in the left hemisphere, especially those that occur before the age of six, may increase the dependence on the right hemisphere. (And remember, the right hemisphere generally controls the left side of the body.)
similarly, Perinatal stressAnd the infant resuscitationAnd the Low birth weight They are all positively correlated with the left hand. This suggests that infection, nutritional deficiencies, hypoxia, and other stressors may influence early brain formation and lateral deviation. In fact, one study using 4D ultrasound found that fetuses were more likely to be infected touch their faces left-handed when mothers reported high levels of stress.
Brain differences in left-handed people
Whether due to genes or environmental stressors, the left brains are slightly different from their right counterparts. Recently Extensive genetic research He found that some genes important for brain development are also linked to dysphoria. The study analyzed data from more than 350,000 people and found that the left was more likely to have differences in three genetic regions important for developing the cellular structures of brain cells.
And easy minds seem less broad and more connected. For example, a meta-analysis of 43 studies found that left-handed people have a The largest corpus callosum (the nerve fibers connecting the left and right hemispheres), and fMRI measurements show that The right and left hemispheres are more connected when using language.
Left-handed and mental illness
How does all this relate to left-wing possession? Higher rates of psychotic disorders? Scientists are still working on the details, but one possible possibility is that The same differences in the brain Left-handedness also contributes to psychotic disorders. Just like dysphoria, patients with psychosis show:
In contrast, researchers believe that these unique brains are more likely to abnormally process stimuli or thoughts, leading to psychosis.
The benefits of hardship
Even if you are left-handed, the chance of developing an acute psychotic disorder is low: the lifetime prevalence rate for the general population is less than 1%, so even if the risk quadrupled, it was still relatively small. And if a psychotic disorder appears, treatment is improving. Moreover, the left is less likely to have other health problems, including ulcers and Parkinson’s disease.
The world is full of healthy and successful people. Four of the last eight US Presidents And many more countries in the world Famous artists, scientists and thinkers He was left-handed or agitated. This may be due to the association of left-handed use with improved verbal performance and increase creativity.
So, while the same brain differences that lead to left-handedness may lead to psychotic disorders, these brain differences also come with benefits for both the individual and the world.