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Right treatment, but not for the left
July 8, 2018, 3:40 pm

Treatment for the most common mental health problems could be ineffective or even detrimental to about 50 percent of the population, according to a new study on areas responsible for emotions in the brain.

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 — was found to be in the left side of the brain, while emotions associated with avoidance —  like disgust and fear — were found housed in the right.

But those studies were done almost exclusively on right-handed people. That simple fact has given us a skewed understanding of how emotion works say researchers at Cornell University in the US. Their study reveals that this longstanding model is, in fact, reversed in left-handed people, whose emotions like alertness and determination are housed in the right side of their brains.

Even more radically, the new research showed that the location of a person's neural systems for emotion depends on whether they are left-handed, right-handed or somewhere in between. According to the new theory, called the ‘sword and shield hypothesis’, the way we perform actions with our hands determines how emotions are organized in our brains.

Sword fighters of old would wield their swords in their dominant hand to attack the enemy — an approach action — and raise their shields with their non-dominant hand to fend off attack — an avoidance action. Consistent with these action habits, results show that approach emotions depend on the hemisphere of the brain that controls the dominant ‘sword’ hand, and avoidance emotions on the hemisphere that controls the non-dominant ‘shield’ hand.

The work has implications for a current treatment for recalcitrant anxiety and depression called neural therapy. Like the technique used in the study, it involves a mild electrical stimulation or a magnetic stimulation to the left side of the brain, to encourage approach-related emotions.

But the new study suggests 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 are probably going to make them worse," noted the researchers.

"And because many people are neither strongly right- nor left-handed, the stimulation will not make any difference for them, because their approach emotions are distributed across both hemispheres," they added.

The study suggests that 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 should not be given the treatment at all.

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