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 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 in the brain, according to Daniel Casasanto, associate professor of human development and psychology at Cornell University.
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. Similar to the technique used in the study and approved by the Food and Drug Administration, it involves a mild electrical stimulation or a magnetic stimulation to the left side of the brain, to encourage approach-related emotions.