Left-handed people could be harmed by ‘shocking’ mental health treatment

19 Jun 2018

Image: Singulyarra/Shutterstock

A radical new theory about how emotions are housed in the brains of left-handed people shows that existing mental health treatments could actually be doing more harm than good.

Those of you who are left-handed will be all too familiar with the many instances where you are forced to use devices designed for right-handed users, such as a pair of scissors or even a guitar.

Now, new research suggests that a type of electrical stimulation treatment – used on both right-handed and left-handed people since the 1970s – for mental health reasons could actually be harmful to the latter because the previous studies it is based on were carried out almost exclusively on right-handed people.

The original studies suggested that each of the brain’s hemispheres is home to a specific type of emotion. They posited that the left hemisphere is linked to emotions approaching and engaging with the world, such as happiness, pride and anger; meanwhile, emotions associated with avoidance – such as anger and disgust – harbour in the right hemisphere.

This has fundamentally skewed our understanding of how emotions are housed in the brain, and now a paper published in Philosophical Transactions of the Royal Society B: Biological Sciences by a team of researchers from Cornell University proposes a new, radical theory.

Daniel Casasanto and his team suggest that the longstanding model is actually reversed in left-handed people, with alertness and determination housed in the right side of their brains.

Additionally, the location of a person’s neural systems for emotion depends on whether they are left-handed, right-handed or somewhere in between.

The ‘sword and shield hypothesis’

Calling it the ‘sword and shield hypothesis’ after the way knights of old would use their strong hand to hold their sword and the weaker one to hold their shield, 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.

If true, these findings have major implications for neural therapy treatment – which involves mild electrical or magnetic stimulation to the left side of the brain – as it means it would be damaging to left-handed patients, decreasing life-affirming approach emotions.

“Because many people are neither strongly right- nor left-handed, the stimulation won’t make any difference for them, because their approach emotions are distributed across both hemispheres,” Casasanto said.

“This suggests strong righties should get the normal treatment, but they make up only 50pc of the population. Strong lefties should get the opposite treatment, and people in the middle shouldn’t get the treatment at all.”

The team stressed, however, that these findings have only been based on healthy patients, and that further clinical research will be needed.

Colm Gorey was a senior journalist with Silicon Republic