Left-handed People Could Be Getting the Wrong Mental Health Treatment, Research Suggests

Most scientific studies into which side of the brain deals with different emotions have focused on right-handed people, and this could mean some treatments for mental illness could not work, or worse, harm left-handed people, researchers believe.

For around four decades, scientists have believed the left side of the brain is in charge of what are known as "approach emotions," which relate to how we approach the world, such as anger and pride. The right side was thought to be linked to avoidance behaviors such as fear.

Hundreds of studies support this view, but the vast majority were carried out on right-handed people. This may have created a false idea of how the brain processes emotions.

Now, researchers at Cornell University believe the handling of approach and avoidance behaviors are based on the dominant and non-dominant sides of our brains, respectively.

Scientists believe the dominant hemisphere of our brains deals with approach emotions. Getty Images

"The 'textbook' model, which holds that positive, approach-related emotions are in the left-hemisphere and negative, avoidance-related emotions are in the right has been validated by hundreds of studies, but this pattern was never predicted, and it's never been explained," Daniel Casasanto, associate professor of human development and psychology at Cornell University, told Newsweek.

The team led by Casasanto believe 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 in the right side of the brain in left-handed people, for example.

To test their hypothesis, scientists stimulated the brains of 25 healthy participants, using a painless electrical current, to see if approach emotions could be triggered, depending on the side of the brain stimulated.

The individuals were stimulated for 20 minutes per day for five days, and noted their feelings of emotions such as pride and happiness before and after the stimulation. The results indicated the dominant side of brains are in control of approach emotions, while the non-dominant side is associated with avoidance.

"This study changes the way we understand not just how emotion is organized in the brain, but also why it's organized that way," professor Casasanto told Newsweek. "Neural circuits for approach-and-avoidance-related emotions piggyback on neural circuits for performing approach-and-avoidance-related actions with our hands. Since righties and lefties tend to perform these actions differently—using opposite hands—emotions follow the opposite organization in their brains."

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 authors of the study, published in Philosophical Transactions of the Royal Society B: Biological Sciences have dubbed this the "sword and shield hypothesis." The name is derived from sword fighters who would hold their swords in their dominant hand to attack and protect themselves with their non-dominant arm.

The findings could change mental health treatments such as neural therapy, in which the left side of the brain is given mild electrical or magnetic stimulation to boost approach emotions. The team fear 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.

This article has been updated with quotes from Professor Daniel Casasanto.