|A left handed man writing his business report. / Photo by: Anastassiya Mdivanian via 123RF|
The brain is one of the most complex organs in the human body comprising two hemispheres, the left, and the right. It is connected by the corpus callosum, a bundle of fibers which acts like a bridge between these two sides. Emotional lateralization, as defined by Wikipedia is the asymmetrical representation of emotional control and processing in the brain. It involves the notion that the right hemisphere conveys negative emotions and the left hemisphere influence positive ones. Now, this triggers the question which side are you on?
Right or Left - Which way?
In a new study published by researchers Geoffrey Brookshire and Daniel Casasanto in the journal Philosophical Transactions of the Royal Society B: Biological Sciences, emotional lateralization, as it’s called, might be more complex than we’ve thought — and, in fact, might be connected to which hand is your dominant one.
After testing both righties and lefties in five experiments, Casasanto - now at the Max Planck Institute for Psycholinguistics - found that righties tend to judge objects on their right side as positive and objects on their left side as negative. Lefties do the opposite by pairing positive things with their left side and negative things with their right.
If you’re familiar with the idea of being “left-brained” or “right-brained,” emotional lateralization is sort of similar: It describes that the left and right hemispheres of the brain are responsible for processing different emotions.
According to an overview of the history of emotional lateralization published in 2008, the big breakthrough for the idea occurred in 1978, when Richard Davidson presented a paper showing evidence that the left prefrontal cortex processes positive emotions, while the right prefrontal cortex processes negative ones. What made this theory so momentous was the fact that it ran counter to what was previously believed — that the right hemisphere processed emotion exclusively, while the left hemisphere processed “intelligence.”
The study entitled, “Approach motivation in human cerebral cortex” emphasized that “approach motivation was lateralized to the same hemisphere that controls the dominant hand” — that is, if you’re right-handed and you take a swing with your sword at an enemy, the motion is connected to the left hemisphere of your brain, while if you’re left-handed, the action is connected to the right hemisphere of the brain. Replace “take a swing with a sword at an enemy” with any other kind of “approach” action.
From there, the question became about how the sword and shield hypothesis might affect emotional lateralization — again, with the understanding that our emotions and our actions are very closely linked. Furthermore, as Casasanto explained it in a press release for the current study, “You would wield the sword in your dominant hand to make approach-related actions like stabbing your enemy, and use the shield in your nondominant hand to fend off attack” — that is, “your dominant hand gets the thing you want and your nondominant hand pushes away the thing you don’t.”
According to him, “Approach motivation should be mediated by the left hemisphere in strong right-handers… it should completely be reversed in strong left-handers… [and] for everyone in the middle of the handedness spectrum, approach emotions should depend on both hemispheres.”
For the study, a sample of 25 adults whose handedness ranged from strong right-handedness to strong left-handedness was exposed to transcranial direct current stimulation — that is, they had the left and right hemispheres of their brains stimulated by an electrical current — for about 20 minutes a day for five days. They also reported how strongly they felt certain approach-related emotions like pride, determination, and enthusiasm both before and after the five days of transcranial direct current stimulation.
These findings totally change our understanding of emotional lateralization. "The big theoretical shift is, we’re saying emotion in the brain isn’t its own system. Emotion in the cerebral cortex is built upon neural systems for motor action,” said Casasanto.
Here's why all these matters for mental health: A type of neural therapy for treating depression and anxiety that has been approved by the Food and Drug Administration (FDA), transcranial magnetic stimulation (TMS), functions quite similarly to the transcranial direct current stimulation used in Brookshire and Casasanto’s study. As the American Psychological Association describes it, TMS operates via a device that sends “short but intense magnetic pulses into the brain, where they generate an electrical current.” These pulses are centered on the left prefrontal cortex and are intended to encourage approach-related emotions.
Neural therapy is somewhat controversial — typically it involves not the application of magnetic or electric currents, but the injection of an anesthetic, which, as Quackwatch points out, is generally not recognized as an effective treatment by the medical community. But for those who seek it out — especially those who seek out TMS — the risk of it not only not working for lefties, but actually causing more problems could very well be an issue.
If you’ve been thinking about trying TMS or something like it, it’s worth considering whether you’re right - or left-handed — and move forward or pull back accordingly.
Left matters just as the Right does
|A left handed comic artist showing her talent. / Photo by: auremar via 123RF|
Since the 1970s, hundreds of studies have suggested that each hemisphere of the brain is home to a specific type of emotion. Emotions linked to approaching and engaging with the world -- like happiness, pride and anger -- lives in the left side of the brain, while emotions associated with avoidance -- like disgust and fear -- are found in the right.
Most of the research that has been conducted on emotional lateralization has focused primarily on right-handed people — which means that both of those previous theories might be completely incorrect. It certainly hasn’t done the 10 percent of the population who are left-handed any favors; indeed, what we’re now discovering is that the way emotional lateralization works for righties may not be the same as the way it works for lefties at all. For lefties, things might be actually reversed.
The “sword and shield” hypothesis focuses on motor control, stemming from the understanding that the actions we take are closely linked with our emotions. The hypothesis describes actions as either “approach” or “avoidance,” noting that approach actions are the sort that is usually performed with someone’s dominant hand, while avoidance actions are usually performed with the nondominant hand.
But these studies have given us a skewed understanding of how emotion works in the brain. Casasanto suggests that the location of a person's neural systems for emotion depends on whether they are left-handed, right-handed or somewhere in between, the research shows.
The work has implications for neural therapy, although the treatment could be damaging for left-handed patients. Stimulation on the left would decrease life-affirming approach emotions. "If you give left-handers the standard treatment, you're probably going to make them worse," he said.
"This suggests strong righties should get the normal treatment, but they make up only 50 percent of the population. Strong lefties should get the opposite treatment, and people in the middle shouldn't get the treatment at all."
However, Casasanto cautions that this research studied only healthy participants and more work is needed to extend these findings to a clinical setting.
The research team believed how the brain deals with emotions in left-handed people is the opposite of right-handed people. Emotions such as alertness and determination are handled on the right side of the brain in left-handed people, for example.
The results mirrored previous studies by the researchers where positive emotions were prompted by stimulating the left-hemisphere of right-handed people’s brains, and visa versa in left-handed individuals.
The findings could change mental health treatments such as administering neural therapy, in which the left side of the brain is given mild electrical or magnetic stimulation to boost approach emotions. The team fears that if the left side of the brain is dominant for a left-handed person, this could have the opposite of the intended effect.
As the research was carried out in healthy individuals, more research is now needed to establish whether this risk is seen in real-life patients.
"Depression and anxiety disorders affect over 20 million Americans. That means a lot of people could be hurt by using treatments predicated on the 'old' model of emotion in the brain," said Casasanto.
With all these considered, further research on left-handed people must be conducted to allow additional response to offer extensive treatments with regards to their mental health.